Photovoltaic delivery system and system operation control method

Abstract

The invention discloses a photovoltaic sending-out system and a system operation control method. The photovoltaic sending-out system comprises a plurality of direct current collection modules, a plurality of high-voltage diode silicon stacks, an alternating current inversion module, a power compensation module and an auxiliary rectification module. The output end of the direct-current collection module is electrically connected with the direct-current bus; the direct-current collection module is used for boosting a direct-current signal output by the photovoltaic panel and then outputting the direct-current signal to a direct-current bus through a corresponding high-voltage diode silicon stack; the alternating-current inversion module is used for converting a direct-current signal on the direct-current bus into an alternating-current signal and outputting the alternating-current signal to an alternating-current power grid; the power compensation module is used for compensating reactive power consumed by the alternating current inversion module; the auxiliary rectification module is used for converting an AC signal on an AC power grid into a DC signal and outputting the DC signal to a DC bus so as to start the AC inversion module. According to the embodiment of the invention, unstable new energy can be collected and sent out at multiple points through direct current collection networking, and the requirement of large-scale grid connection of the new energy is met.

Description

Technical Field

[0001] The present application belongs to the field of new energy power generation technology, and in particular relates to a photovoltaic transmission system and a system operation control method. Background Art

[0002] In the field of new energy power generation, with the rapid growth of photovoltaic installed capacity, traditional AC collection systems have gradually exposed technical bottlenecks, seriously restricting the large-scale and efficient grid connection of new energy.

[0003] Traditional AC collection systems typically use multi-stage AC / DC and DC / AC conversion to connect photovoltaic power to the grid. This complex conversion process not only reduces system efficiency but also increases the risk of system instability. Multi-stage power electronic conversion is prone to harmonic resonance and voltage fluctuations, requiring the deployment of a large number of additional capacitor banks or power compensation modules to maintain voltage stability, which increases costs. Furthermore, the traditional single-point fault propagation mechanism means that a single module failure can cause a complete system crash, making it difficult to meet the stringent reliability and safety requirements of large-scale renewable energy grid integration.

[0004] Therefore, traditional AC collection systems have significant defects in efficiency, stability, safety, flexibility and economy, and are unable to meet the needs of large-scale grid connection of new energy. Summary of the Invention

[0005] The embodiment of the present application provides a photovoltaic transmission system and a system operation control method. Through DC collection and networking, the energy conversion links are significantly reduced, and large-scale new energy can be efficiently and flexibly connected. It has independent power control capabilities and can dynamically adjust the output power according to the needs of the power grid. It can significantly enhance the voltage support capability, collect and transmit unstable new energy at multiple points, improve the grid connection safety and stability of new energy, solve the problems of AC collection system in efficiency, stability, safety, flexibility and economy, and meet the needs of large-scale grid connection of new energy.

[0006] In a first aspect, an embodiment of the present application provides a photovoltaic transmission system, comprising:

[0007] A plurality of DC collection modules, wherein the output ends of the DC collection modules are electrically connected to the DC bus;

[0008] Multiple high-voltage diode silicon stacks, DC collection modules correspond one to one with the high-voltage diode silicon stacks, and the DC collection modules are used to boost the DC signal output by the photovoltaic panel and output it to the DC bus through the corresponding high-voltage diode silicon stack;

[0009] AC inverter module, used to convert the DC signal on the DC bus into an AC signal and output it to the AC grid;

[0010] Power compensation module, used to compensate for the reactive power consumed by the AC inverter module;

[0011] The auxiliary rectifier module is used to convert the AC signal on the AC power grid into a DC signal and output it to the DC bus to start the AC inverter module.

[0012] In a possible embodiment of the first aspect, the DC collection module includes a plurality of collection sub-modules, and output ends of the plurality of collection sub-modules are connected in series to serve as the output end of the DC collection module.

[0013] In a possible embodiment of the first aspect, the aggregation submodule includes:

[0014] Maximum power point tracking module, used to track the maximum power output point of the photovoltaic panel so that the photovoltaic panel can output the maximum available power;

[0015] The boost module is used to boost the DC signal output by the photovoltaic panel to a preset level and output it. The output end of the boost module serves as the output end of the collection submodule.

[0016] In a possible embodiment of the first aspect, the boost module includes:

[0017] An inverter circuit, whose input terminal serves as an input terminal of a boost module;

[0018] a resonant circuit, an input end of which is electrically connected to the first output end of the inverter circuit;

[0019] a transformer, a first input end of which is electrically connected to the output end of the resonant circuit, and a second input end of which is electrically connected to the second output end of the inverter circuit;

[0020] The rectifier circuit has an input end electrically connected to the output end of the transformer, and an output end serving as the output end of the boost module.

[0021] In a possible embodiment of the first aspect, the AC inverter module includes a reverse-resistance integrated gate-commutated thyristor.

[0022] Based on the same inventive concept, in a second aspect, an embodiment of the present application further provides a system operation control method, which is applied to the photovoltaic transmission system as described in any embodiment of the first aspect, and the method includes:

[0023] Get information about the light intensity in the area where the photovoltaic panels are located;

[0024] When the light intensity is greater than or equal to a first preset light intensity threshold, the auxiliary rectifier module is used to convert the AC signal on the AC grid into a DC signal and then output it to the DC bus to start the AC inverter module;

[0025] When the power of the photovoltaic panel reaches a first preset power threshold and lasts for a preset time, the plurality of DC collection modules are started.

[0026] In a possible embodiment of the second aspect, when the power of the photovoltaic panel reaches a preset power and lasts for a preset time, starting multiple DC collection modules includes:

[0027] When the power of the photovoltaic panel reaches a preset power and lasts for a preset time, the multiple DC collection modules are started in sequence according to the preset time intervals.

[0028] In a possible embodiment of the second aspect, the present invention further includes:

[0029] When the light intensity is less than a second preset light intensity threshold and the sum of the output powers of the plurality of DC collection modules is less than a second preset power threshold, the plurality of DC collection modules and the AC inverter modules are sequentially shut down at preset time intervals.

[0030] In a possible embodiment of the second aspect, the DC collection module includes a plurality of collection sub-modules, each collection sub-module including a maximum power point tracking module; and the method further includes:

[0031] In the case that the electrical signal output by the AC inverter module drops abnormally, the maximum power point tracking module is used to exit the maximum power point tracking mode, and the power compensation module is used to switch to the reactive power injection mode.

[0032] In a possible embodiment of the second aspect, the present invention further includes:

[0033] When the electrical signal output by the AC inverter module increases abnormally, the power value output by the maximum power point tracking module is obtained;

[0034] When the power value output by the maximum power point tracking module is greater than the third preset power threshold, the maximum power point tracking module is used to output a target power value, the target power value is less than or equal to the third preset power threshold, and the power compensation module is used to switch to the reactive absorption mode.

[0035] The photovoltaic transmission system and system operation control method of the embodiment of the present application include a plurality of DC collection modules, a plurality of high-voltage diode silicon stacks, an AC inverter module, a power compensation module and an auxiliary rectifier module. The output end of the DC collection module is electrically connected to the DC bus. The parallel structure of the plurality of DC collection modules makes each DC collection module independent of each other, allowing a single DC collection module to automatically exit when a fault occurs, while the remaining DC collection modules continue to operate, avoiding the risk of system-wide collapse caused by traditional single-point failures, improving the reliability and stability of the system, and the system can increase or decrease the number of DC collection modules according to demand, with flexible scalability. The high-voltage diode silicon stack is composed of a plurality of high-voltage diodes connected in series, which can ensure the stable operation of the system. The high-voltage diode silicon stack is set in a one-to-one correspondence with the DC collection module. The DC collection module can boost the DC signal output by the photovoltaic panel and output it to the DC bus through the corresponding high-voltage diode silicon stack. The AC inverter module is used to convert the DC signal on the DC bus into an AC signal and output it to the AC power grid, facilitating connection with the AC power grid and power transmission. The power compensation module is used to dynamically compensate for the reactive power consumed by the AC inverter module, which helps to maintain the stable operation of the power grid and improve the power quality. The auxiliary rectifier module is used to convert the AC signal on the AC power grid into a DC signal and then output it to the DC bus to start the AC inverter module and ensure that the AC inverter module can start smoothly. The photovoltaic transmission system of the embodiment of the present application significantly reduces the energy conversion link through DC collection networking, can achieve large-scale efficient and flexible access to new energy, has independent power control capabilities, can dynamically adjust the output power according to the needs of the power grid, can significantly enhance the voltage support capability, and can collect and transmit unstable new energy at multiple points, improve the grid connection safety and stability of new energy, and solve the problems of existing AC collection systems in terms of efficiency, stability, safety, flexibility and economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Other features, objects and advantages of the present application will become more apparent by reading the following detailed description of non-limiting embodiments with reference to the accompanying drawings, in which the same or similar reference numerals represent the same or similar features and the accompanying drawings are not drawn to scale.

[0037] Figure 1 This is a structural diagram of a photovoltaic transmission system provided in an embodiment of the present application;

[0038] Figure 2 This is a structural diagram of a DC collection module in a photovoltaic transmission system provided in an embodiment of the present application;

[0039] Figure 3 This is a structural diagram of a collection submodule in a photovoltaic transmission system provided in an embodiment of the present application;

[0040] Figure 4This is a structural diagram of a boost module in a photovoltaic transmission system provided in an embodiment of the present application;

[0041] Figure 5 This is a schematic diagram of phase commutation when a drop fault occurs at the output end of an AC inverter module in a photovoltaic transmission system provided by an embodiment of the present application;

[0042] Figure 6 This is a flow chart of the system operation control method provided in an embodiment of the present application;

[0043] Figure 7 This is another flow chart of the system operation control method provided in the embodiment of the present application;

[0044] Figure 8 This is another flow chart of the system operation control method provided in the embodiment of the present application;

[0045] Figure 9 This is another flow chart of the system operation control method provided in the embodiment of the present application. DETAILED DESCRIPTION

[0046] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present application and are not configured to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is merely to provide a better understanding of the present application by illustrating the examples of the present application.

[0047] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, the elements defined by the phrase "comprising..." do not exclude the presence of other identical elements in the process, method, article, or device comprising the elements.

[0048] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0049] It will be apparent to those skilled in the art that various modifications and variations can be made in this application without departing from the spirit or scope of this application. Therefore, this application is intended to cover modifications and variations of this application that fall within the scope of the corresponding claims (technical solutions claimed for protection) and their equivalents. It should be noted that the embodiments provided in the examples of this application can be combined with each other without contradiction.

[0050] Before describing the technical solutions provided by the embodiments of the present application, in order to facilitate understanding of the embodiments of the present application, the present application first specifically describes the problems existing in the related art:

[0051] In the field of new energy power generation, with the rapid growth of photovoltaic installed capacity, the AC collection system in related technologies has gradually exposed technical bottlenecks, seriously restricting the large-scale and efficient grid connection of new energy.

[0052] The AC collection system in related technologies usually uses multi-stage AC / DC and DC / AC conversion to achieve the connection of photovoltaic power to the grid. This complex conversion link not only reduces the efficiency of the system, but also increases the risk of system instability. Multi-stage power electronic conversion is prone to cause harmonic resonance and voltage fluctuations, and a large number of capacitor banks or power compensation module devices need to be additionally configured to maintain voltage stability, which increases costs. In addition, the traditional single-point fault propagation mechanism causes a single module failure to cause the entire system to collapse, which makes it difficult to meet the stringent requirements of reliability and safety for large-scale grid connection of new energy. Therefore, the AC collection system in related technologies has significant defects in efficiency, stability, safety, flexibility and economy, and it is difficult to meet the needs of large-scale grid connection of new energy.

[0053] Based on this, the embodiment of the present application provides a photovoltaic transmission system and a system operation control method. Through DC collection and networking, the energy conversion links are significantly reduced, and large-scale new energy can be efficiently and flexibly accessed. It has independent power control capabilities and can dynamically adjust the output power according to grid demand. It can significantly enhance the voltage support capability, collect and transmit unstable new energy at multiple points, improve the grid connection safety and stability of new energy, and solve the problems of AC collection system in efficiency, stability, safety, flexibility and economy.

[0054] The photovoltaic transmission system provided in the embodiments of the present application is described in detail below with reference to the accompanying drawings.

[0055] Figure 1 This is a schematic diagram of a photovoltaic transmission system structure provided by an embodiment of the present application. Figure 1 As shown, the photovoltaic transmission system 100 may include a plurality of DC collection modules 10 , a plurality of high-voltage diode silicon stacks 20 , an AC inverter module 30 , a power compensation module 40 and an auxiliary rectifier module 50 .

[0056] The output end of the DC collection module 10 is electrically connected to the DC bus.

[0057] Specifically, the output ends of multiple DC collection modules 10 are electrically connected to the DC bus respectively, that is, the output ends of multiple DC collection modules 10 are electrically connected to the DC bus after being connected in parallel. The parallel structure of multiple DC collection modules 10 makes each DC collection module 10 independent of each other, allowing a single DC collection module 10 to automatically exit when a fault occurs, while the remaining DC collection modules 10 continue to operate, avoiding the risk of system-wide collapse caused by traditional single-point failures, improving the reliability and stability of the system, and the system can increase or decrease the number of DC collection modules 10 according to demand, with flexible scalability.

[0058] The DC collection module 10 corresponds to the high-voltage diode silicon stack 20 on a one-to-one basis. The DC collection module 10 is used to boost the DC signal output by the photovoltaic panel 200 and output it to the DC bus through the corresponding high-voltage diode silicon stack 20 .

[0059] The photovoltaic panel 200 can convert light energy into electrical energy.

[0060] Specifically, the high-voltage diode silicon stack 20 is composed of multiple high-voltage diodes connected in series. The high-voltage diode silicon stack 20 has high voltage and impact resistance, can prevent current backflow, suppress voltage fluctuations, and improve system stability. The high-voltage diode silicon stack 20 is set in a one-to-one correspondence with the DC integration module 10. The DC integration module 10 can boost the DC signal output by the photovoltaic panel 200 and output it to the DC bus through the corresponding high-voltage diode silicon stack 20. Each DC integration module 10 independently boosts the DC signal and outputs it through the corresponding high-voltage diode silicon stack 20, reducing energy loss, preventing current backflow, and ensuring stable operation of the system.

[0061] The AC inverter module 30 is used to convert the DC signal on the DC bus into an AC signal and output it to the AC grid.

[0062] Specifically, the AC inverter module 30 converts the DC signal on the DC bus into an AC signal and outputs it to the AC grid, facilitating connection to the AC grid and power transmission. Using a unified AC inverter module for centralized inversion offers advantages such as centralized control, optimized efficiency, reduced costs, simplified maintenance, improved power quality, and intelligent expansion, significantly enhancing the cost-effectiveness, reliability, and flexibility of the photovoltaic transmission system 100.

[0063] The power compensation module 40 is used to compensate for the reactive power consumed by the AC inverter module 30 .

[0064] Specifically, the power compensation module 40 is used to dynamically compensate for the reactive power consumed by the AC inverter module 30, that is, the reactive power output by the power compensation module 40 is equal to the reactive power consumed by the AC inverter module 30, which helps to maintain the stable operation of the power grid and improve the power quality.

[0065] The auxiliary rectifier module 50 is used to convert the AC signal on the AC grid into a DC signal and output it to the DC bus to start the AC inverter module 30 .

[0066] Specifically, the auxiliary rectifier module 50 can convert the AC signal on the AC power grid into a DC signal and output it to the DC bus to start the AC inverter module 30 , thereby ensuring smooth startup of the AC inverter module 30 .

[0067] The photovoltaic transmission system and system operation control method of the embodiment of the present application include a plurality of DC collection modules 10, a plurality of high-voltage diode silicon stacks 20, an AC inverter module 30, a power compensation module 40 and an auxiliary rectifier module 50. The output end of the DC collection module 10 is electrically connected to the DC bus. The parallel structure of the plurality of DC collection modules 10 makes each DC collection module 10 independent of each other, allowing a single DC collection module 10 to automatically exit when a fault occurs, while the remaining DC collection modules 10 continue to operate, avoiding the risk of system-wide collapse caused by traditional single-point failures, improving the reliability and stability of the system, and the system can increase or decrease the number of DC collection modules 10 according to demand, with flexible scalability. The high-voltage diode silicon stack 20 is composed of a plurality of high-voltage diodes connected in series. The high-voltage diode silicon stack 20 is set one-to-one with the DC collection module 10. The DC collection module 10 can boost the DC signal output by the photovoltaic panel 200 and output it to the DC bus through the corresponding high-voltage diode silicon stack 20, which can ensure the stable operation of the system. The AC inverter module 30 is used to convert the DC signal on the DC bus into an AC signal and output it to the AC power grid, facilitating connection to the AC power grid and power transmission. The power compensation module 40 is used to dynamically compensate for the reactive power consumed by the AC inverter module 30, helping to maintain the stable operation of the power grid and improve the quality of power. The auxiliary rectifier module 50 is used to convert the AC signal on the AC power grid into a DC signal and output it to the DC bus to start the AC inverter module 30 and ensure that the AC inverter module 30 can start smoothly. The photovoltaic transmission system of the embodiment of the present application significantly reduces the energy conversion link through DC aggregation networking, enabling efficient and flexible access to large-scale new energy. It has independent power control capabilities and can dynamically adjust output power according to grid demand. It can significantly enhance voltage support capabilities, aggregate and transmit unstable new energy at multiple points, improve the safety and stability of new energy grid connection, solve the problems of existing AC aggregation systems in efficiency, stability, safety, flexibility and economy, and meet the needs of large-scale new energy grid connection.

[0068] Figure 2 It is a structural diagram of a DC collection module 10 in a photovoltaic transmission system provided in an embodiment of the present application.

[0069] In some embodiments, as Figure 2 As shown, the DC collection module 10 includes a plurality of collection sub-modules 11 , and the output ends of the plurality of collection sub-modules 11 are connected in series to serve as the output end of the DC collection module 10 .

[0070] The DC integration module 10 in the present embodiment employs a design in which the output terminals of multiple integration submodules 11 are connected in series. This significantly increases the output voltage level of the DC integration module 10 through a voltage superposition effect, thereby matching the requirements of the DC grid and reducing the need for subsequent voltage boosting. This structure allows each integration submodule 11 to bear only a portion of the current stress, reducing power loss and enhancing reliability.

[0071] Figure 3 It is a structural diagram of the collection submodule 11 in the photovoltaic transmission system provided in an embodiment of the present application.

[0072] In some embodiments, as Figure 3 As shown, the integration submodule 11 may include a maximum power point tracking module 111 and a boost module 112 .

[0073] The maximum power point tracking module 111 is used to track the maximum power output point of the photovoltaic panel 200 so that the photovoltaic panel 200 can output the maximum available power.

[0074] The boost module 112 is used to boost the DC signal output by the photovoltaic panel 200 to a preset level and output it. The output end of the boost module 112 serves as the output end of the collection submodule 11 .

[0075] The collection submodule 11 in the present embodiment integrates a maximum power point tracking module 111 and a boost module 112 to maximize and efficiently transmit the output power of the photovoltaic panel 200. The maximum power point tracking module 111 adjusts the operating state of the photovoltaic panel 200 in real time, ensuring that it always operates at its maximum power output point, thereby improving the energy conversion efficiency of the photovoltaic panel 200 and reducing power losses caused by environmental factors. Simultaneously, the boost module 112 boosts the low-voltage DC power output of the photovoltaic panel 200 to a preset level, meeting subsequent voltage requirements.

[0076] Figure 4 It is a structural diagram of the boost module 112 in the photovoltaic transmission system provided in an embodiment of the present application.

[0077] In some embodiments, as Figure 4 As shown, the boost module 112 may include an inverter circuit 1121 , a resonant circuit 1122 , a transformer 1123 and a rectifier circuit 1124 .

[0078] An input end of the inverter circuit 1121 serves as an input end of the boost module 112 .

[0079] An input end of the resonant circuit 1122 is electrically connected to a first output end of the inverter circuit 1121 .

[0080] A first input end of the transformer 1123 is electrically connected to the output end of the resonant circuit 1122 , and a second input end of the transformer 1123 is electrically connected to the second output end of the inverter circuit 1121 .

[0081] An input end of the rectifier circuit 1124 is electrically connected to an output end of the transformer 1123 , and an output end of the rectifier circuit 1124 serves as an output end of the boost module 112 .

[0082] In the embodiment of the present application, the boost module 112 converts direct current into high-frequency alternating current through the inverter circuit 1121, implements soft switching through the resonant circuit 1122 to reduce switching losses, and then performs voltage conversion and electrical isolation through the transformer 1123. Finally, the rectifier circuit 1124 outputs stable high-voltage direct current. This structure significantly reduces switching losses by utilizing resonant soft switching technology. Combined with the high-frequency isolation characteristics of the transformer, it not only achieves efficient boosting, but also reduces electromagnetic interference, while improving the safety and stability of the system through electrical isolation.

[0083] It should be noted that the inventors have found that the series resonant boost module 112 (see Figure 4 ), with advantages such as simple structure, single-phase power flow, easy soft switching implementation, high degree of modularity, and fast dynamic response. Due to the unidirectional power transmission of the entire photovoltaic collection system, the boost module 112 can be designed using a unidirectional series resonant topology. The low-voltage side uses an IGCT-based full-bridge switching circuit, and the high-voltage side uses a series diode uncontrolled rectifier circuit. It primarily comprises a full-bridge converter (inverter circuit 1121), a diode bridge (rectifier circuit 1124), and a medium-frequency magnetic integrated isolation transformer (operating frequency 800-1000Hz). The medium-frequency magnetic integrated transformer (including resonant circuit 1122 and transformer 1123) connects the AC sides of inverter circuit 1121 and rectifier circuit 1124 to provide electrical isolation and voltage conversion.

[0084] In some embodiments, the AC inverter module 30 may include a reverse-resistance integrated gate-commutated thyristor.

[0085] Specifically, after photovoltaic power is collected through DC, it needs to be inverted into AC voltage before it can be connected to the grid. Line commutation converter LCC technology is most widely used in the field of high-voltage DC transmission due to its long distance, large capacity and high stability, but it has the inherent problem of commutation failure. The embodiment of the present application proposes an AC inverter module 30 including a reverse blocking integrated gate commutated thyristor. Its commutation principle is similar to that of LCC. The difference is that the embodiment of the present application replaces the traditional thyristor device with a fully controlled IGCT reverse blocking device (reverse blocking integrated gate commutated thyristor, RB-IGCT) with active shutdown capability, which can completely eliminate the risk of commutation failure. When the HCC valve is operating normally, it is consistent with the LCC valve. At the same time, a high-power reverse blocking integrated gate commutated thyristor is used. Compared with the thyristor in the traditional valve, the reverse blocking IGCT can withstand the forward voltage without reverse recovery time due to the presence of gate drive, so the device recovery ability is enhanced. The HCC valve (AC inverter module 30) has the ability to actively shut off the current, so it can resist commutation failure. The process is as follows. Figure 5 When a major grid fault occurs, the valve-side AC line voltage drops to a level that prevents commutation. The HCC converter valve relies on the reverse-resistance IGCT's shutdown capability to cut off the current in its arm, forcing the current to commutate to the next arm, thus preventing commutation failure. This operating mode requires an additional shutdown signal to ensure reliable and safe shutdown of the converter valve arm.

[0086] In the embodiment of the present application, a reverse-blocking integrated gate-commutated thyristor (IGCT) is configured in the AC inverter module 30, and efficient and accurate current control is achieved through its active controllable shutdown capability. The AC inverter module 30 using the reverse-resistance integrated gate-commutated thyristor (RB-IGCT) completely solves the commutation failure problem of the traditional line-commutated converter LCC technology through its active shutdown capability. Its core advantages are reflected in: when the AC voltage drops due to a grid fault, the reverse-resistance integrated gate-commutated thyristor (RB-IGCT) can forcibly cut off the current of the faulty bridge arm and drive the commutation to the next bridge arm without relying on the natural zero crossing of the grid voltage, so that the system has millisecond-level fault ride-through capability; compared with the traditional line-commutated converter LCC that requires the configuration of a complex commutation capacitor group and a lockout protection circuit, the embodiment of the present application achieves intrinsic safety through device-level active control, solving the commutation failure problem; in addition, the bipolar blocking characteristics (forward and reverse voltage tolerance) of the reverse-resistance integrated gate-commutated thyristor (RB-IGCT) combined with the gate drive control reduce device switching losses and thermal stress, significantly improving the operational reliability and economy of the photovoltaic grid-connected system.

[0087] It should be noted that the photovoltaic transmission system of the embodiment of the present application adopts a large-scale photovoltaic DC collection and centralized inversion grid-connected topology based on DC inverter technology, which can give full play to the current-carrying capacity of large-capacity fully controlled power devices to reduce engineering costs, while solving the inherent commutation failure problem, improving reliability, reducing the collection and grid-connected system losses, and improving efficiency. Through the series boosting of the high-voltage side of the boost module 112 and the photovoltaic DC collection based on DC centralized inversion, the system can operate smoothly. The grid-connected AC inverter module 30 adopts a hybrid commutation converter (HCC) with the ability to resist commutation failure, which has good technical and economic benefits. Equipped with a power compensation module SVG, the system has the ability to ride through AC side faults and can adapt to large-scale, low-cost photovoltaic collection and transmission application scenarios.

[0088] In one example, the photovoltaic transmission system 100 is a 50MW photovoltaic system. The photovoltaic transmission system 100 includes five DC collection modules 10. The DC collection modules 10 are connected to the DC bus through corresponding high-voltage diode silicon stacks 20. The DC collection modules 10 are independent of each other. The operation of the DC collection modules 10 after a failure does not affect the normal operation of other DC collection modules 10. In each 10MW DC collection module 10, the maximum power point tracking module 111 (MPPT) uses a Boost product to achieve decentralized MPPT control of the photovoltaic array. The individual boost modules 112 in each 10MW DC collection module 10 are composed of "low-voltage side (input end) parallel connection - high-voltage side (output end) series connection" mode. The five DC collection modules 1 are connected in parallel to the ±15kV DC bus. After being combined, they are inverted by the hybrid commutation converter HCC (AC inverter module 30) and connected to the AC grid. Since the hybrid commutation converter HCC (AC inverter module 30 ) needs to consume 40% to 60% of reactive power during operation, the power compensation module 40 can provide reactive power support and harmonic control functions.

[0089] It should be noted that the output ends of the boost modules 112 can be connected in series or in parallel, that is, the topological schemes of photovoltaic DC boost collection can be divided into two types: parallel networking (multiple boost module 112 output ends are connected in parallel) and series networking (multiple boost module 112 output ends are connected in series). Due to the parallel DC collection networking scheme, the design of the high-ratio boost module 112 needs to be considered. The voltage stress of the electronic circuit of the boost module 112 may be too high and voltage balancing is more difficult. The series collection method adopts a cascade design on the output side of the boost module 112, which can achieve an increase in the transmission voltage level and at the same time reduce the design difficulty of the high-ratio DC transformer.

[0090] Figure 6 It is a flow chart of the system operation control method provided in an embodiment of the present application.

[0091] Based on the same inventive concept, the embodiment of the present application further provides a system operation control method, which is applied to the photovoltaic transmission system 100 as described in any of the above embodiments. Figure 6 As shown, the method may include steps S110 to S130.

[0092] S110 , obtaining information on light intensity in the area where the photovoltaic panel 200 is located.

[0093] S120 , when the light intensity is greater than or equal to the first preset light intensity threshold, the auxiliary rectifier module 50 is used to convert the AC signal on the AC grid into a DC signal and then output it to the DC bus to start the AC inverter module 30 .

[0094] S130 , when the power of the photovoltaic panel 200 reaches a first preset power threshold and lasts for a preset time, starting the plurality of DC collection modules 10 .

[0095] It should be noted that the inventors have discovered that, since photovoltaics is an intermittent and unstable energy source, there is a problem of no electricity generation at night and possible obstruction during the day. In order to ensure that the photovoltaic collection system can transmit electricity as stably as possible, it is possible to choose whether to configure energy storage based on the actual situation of the project location and the investment cost.

[0096] The embodiment of the present application can monitor the light intensity in real time. When the light intensity is greater than or equal to the first preset light intensity threshold (such as in the morning), the auxiliary rectifier module 50 is first used to draw power from the AC power grid to start the AC inverter module 30, ensuring that the AC inverter module 30 increases the power to a steady state (such as 0.1 pu); after the output power of the photovoltaic panel 200 stably reaches the first preset power threshold (such as 0.2 pu) and lasts for a preset time (such as half an hour), the DC collection module 10 is activated to transmit power. At this time, the photovoltaic transmission system is mainly in a unidirectional power grid-connected mode (operation mode). This control logic avoids false startup caused by short-term light fluctuations through the dual-condition judgment of light and power. At the same time, the auxiliary rectifier module 50 can be used to draw power from the AC power grid to pre-start the AC inverter module 30, thereby improving the success rate of system startup and extending the life of the equipment.

[0097] Figure 7 This is another flow chart of the system operation control method provided in the embodiment of the present application.

[0098] In some embodiments, as Figure 7 As shown, step S130 may include step S131 when the power of the photovoltaic panel 200 reaches a preset power and lasts for a preset time period, starting multiple DC collection modules 10.

[0099] S131 , when the power of the photovoltaic panel 200 reaches a preset power and lasts for a preset time, the plurality of DC collection modules 10 are started in sequence according to preset time intervals.

[0100] The embodiment of the present application reduces the instantaneous current impact caused by simultaneous startup through the staggered startup mechanism, thereby ensuring system stability.

[0101] Figure 8 This is another flow chart of the system operation control method provided in the embodiment of the present application.

[0102] In some embodiments, as Figure 8 As shown, the system operation control method may further include step S140.

[0103] S140 , when the light intensity is less than a second preset light intensity threshold and the sum of the output powers of the plurality of DC collection modules 10 is less than a second preset power threshold, shutting down the plurality of DC collection modules 10 and the AC inverter module 30 in sequence according to a preset time interval.

[0104] In the embodiment of the present application, when there is insufficient light (the light intensity is less than the second preset light intensity threshold) and the sum of the output powers of multiple DC collection modules 10 is less than the second preset power threshold (such as in the evening), the DC collection module 10 and the AC inverter module 30 can be shut down in sequence, avoiding energy loss caused by ineffective operation. The orderly shutdown mechanism reduces the mechanical stress of frequent start and stop of equipment, extends the life of key components, and prevents false shutdowns caused by short-term light fluctuations through power-light dual condition judgment, ensuring the stability of the system in critical operating conditions, and significantly improving the economy and operational reliability of the system.

[0105] It should be noted that the photovoltaic transmission system primarily operates in two modes: one-way power grid-connected mode (operating mode) and one-way power grid-connected mode (off-operating mode). During periods of severe light insufficiency (nighttime to early morning hours), characterized by no light or low light conditions, the photovoltaic transmission system equipment is deactivated (off-operating mode). The AC inverter module 30 and boost module 112, among other components, are all shut down, with the isolation switch open and the ground switch connected to ground.

[0106] In one example, when the total annual solar radiation is stable, the daily start-stop control strategy of the photovoltaic transmission system is as follows:

[0107] (1) From night to early morning (when the light intensity is seriously insufficient), there is no light or low light conditions, and all the equipment in the system will not start.

[0108] (2) Every morning (when the light intensity is greater than or equal to the first preset light intensity threshold), the auxiliary rectifier power supply 50 unlocks the AC inverter module 30 in the constant current control mode and increases the power to a steady state of 0.1 pu. After the light power (the power of the photovoltaic panel 200) reaches the preset power (e.g., 0.2 pu) and continues to operate for half an hour, the boost module 112 and the maximum power point tracking module 111 in the five DC collection modules 10 are unlocked in sequence, allowing the photovoltaic system to transmit power. At this time, the auxiliary rectifier power supply 50 can reduce the power to 0 and then lock and exit the system.

[0109] (3) In the evening when there is insufficient light (light intensity is less than the second preset light intensity threshold) and the sum of the output powers of multiple DC collection modules 10 is less than the second preset power threshold, the shutdown process is: locking the DC collection module 10 and locking the AC inverter module 30, which can avoid the instability of the AC inverter module 30 caused by current discontinuity, and the system can exit operation as soon as possible.

[0110] The embodiment of the present application adopts the pre-start logic of "building voltage first and then injecting light" during the morning startup phase, and uses the auxiliary rectifier power supply to pre-complete the soft start and voltage stabilization (0.1pu steady state) of the AC inverter module. After the photovoltaic output is stable (≥0.2pu) and lasts for 30 minutes to verify the system reliability, the DC collection module is started, thereby improving the system startup success rate; during the nighttime shutdown phase, the sequential shutdown is triggered by the dual conditions of light and power, and the DC module is locked first before the AC inverter module is safely exited, thereby avoiding current shocks to the equipment and extending the life of key components.

[0111] It should be noted that normal start and stop and fault response are the two main control functions of the system control layer. AC grid faults can cause abnormal drops or increases in the electrical signal at the output of the AC inverter module.

[0112] Figure 9 This is another flow chart of the system operation control method provided in the embodiment of the present application.

[0113] In some embodiments, the DC collection module 10 may include a plurality of collection submodules 11, and the collection submodule 11 may include a maximum power point tracking module 111. Figure 9 As shown, the system operation control side may further include step S150.

[0114] S150 , when the electrical signal output by the AC inverter module 30 drops abnormally, the maximum power point tracking module 111 is used to exit the maximum power point tracking mode, and the power compensation module 40 is used to switch to the reactive power injection mode.

[0115] In the embodiment of the present application, when an AC power grid fault causes an abnormal drop in the electrical signal at the output of the AC inverter module 30, by exiting the maximum power point tracking (MPPT) mode, for example, by maintaining the MPPT duty cycle signal consistent with that before the fault, the photovoltaic panel 200 can avoid problems such as DC bus voltage loss or equipment overstress caused by forced tracking of the maximum power point, thereby reducing the voltage fluctuation amplitude on the DC side during a drop fault and effectively protecting power devices from voltage shocks. At the same time, the power compensation module quickly switches to the reactive power injection mode, which can increase the output voltage of the AC inverter module 30 by injecting reactive power into the power grid, thereby improving the operational reliability of the system under abnormal power grid conditions.

[0116] In some embodiments, you can continue to see Figure 9 The system operation control part may also include S161 and S162.

[0117] S161 , when the electrical signal output by the AC inverter module 30 increases abnormally, obtaining the power value output by the maximum power point tracking module 111 .

[0118] S162, when the power value output by the maximum power point tracking module 111 is greater than the third preset power threshold, the maximum power point tracking module 111 is used to output a target power value, the target power value is less than or equal to the third preset power threshold, and the power compensation module 40 is used to switch to the reactive absorption mode.

[0119] In the embodiment of the present application, when the electrical signal at the output end of the AC inverter module 30 increases abnormally due to an AC power grid fault, the output power of the maximum power point tracking module 111 is limited (≤ a third preset power threshold), thereby reducing the DC bus voltage fluctuation amplitude and preventing power devices from breaking down due to overvoltage; at the same time, the power compensation module 40 switches to the reactive absorption mode, which can dynamically consume reactive power, effectively suppressing voltage over-limit, and enabling the system to have AC side fault ride-through capability.

[0120] It should be understood that in the embodiments of the present application, "B corresponding to A" means that B is associated with A and B can be determined based on A. However, it should also be understood that determining B based on A does not mean determining B based solely on A, but B can also be determined based on A and / or other information.

[0121] The above are only specific embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and such modifications or substitutions should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A photovoltaic transmission system, characterized in that: include: A plurality of DC collection modules, wherein the output ends of the DC collection modules are electrically connected to the DC bus; A plurality of high-voltage diode silicon stacks, wherein the DC collection modules correspond one to one with the high-voltage diode silicon stacks, and the DC collection modules are used to boost the DC signal output by the photovoltaic panel and output it to the DC bus through the corresponding high-voltage diode silicon stack; an AC inverter module, configured to convert the DC signal on the DC bus into an AC signal and output the signal to the AC grid; A power compensation module, used to compensate for the reactive power consumed by the AC inverter module; The auxiliary rectifier module is used to convert the AC signal on the AC power grid into a DC signal and output it to the DC bus to start the AC inverter module.

2. The photovoltaic transmission system according to claim 1, characterized in that: The DC collection module includes a plurality of collection submodules, and the output ends of the plurality of collection submodules are connected in series to serve as the output end of the DC collection module.

3. The photovoltaic transmission system according to claim 2, characterized in that: The collection submodule includes: A maximum power point tracking module, configured to track the maximum power output point of the photovoltaic panel so that the photovoltaic panel outputs maximum available power; The boost module is used to boost the DC signal output by the photovoltaic panel to a preset level and output it, and the output end of the boost module serves as the output end of the collection submodule.

4. The photovoltaic transmission system according to claim 3, characterized in that: The boost module comprises: an inverter circuit, whose input terminal serves as the input terminal of the boost module; a resonant circuit, an input end of which is electrically connected to the first output end of the inverter circuit; a transformer, a first input end of which is electrically connected to the output end of the resonant circuit, and a second input end of which is electrically connected to the second output end of the inverter circuit; The rectifier circuit has an input end electrically connected to the output end of the transformer, and an output end serving as the output end of the boost module.

5. The photovoltaic transmission system according to claim 1, characterized in that: The AC inverter module includes a reverse resistance integrated gate commutated thyristor.

6. A system operation control method, characterized in that: Applied to the photovoltaic transmission system according to any one of claims 1 to 5, the method comprises: Get information about the light intensity in the area where the photovoltaic panels are located; When the light intensity is greater than or equal to a first preset light intensity threshold, the auxiliary rectifier module is used to convert the AC signal on the AC grid into a DC signal and then output it to the DC bus to start the AC inverter module; When the power of the photovoltaic panel reaches a first preset power threshold and lasts for a preset time, a plurality of DC collection modules are started.

7. The method according to claim 6, characterized in that When the power of the photovoltaic panel reaches a preset power and lasts for a preset time, starting multiple DC collection modules includes: When the power of the photovoltaic panel reaches a preset power and lasts for a preset time, a plurality of DC collection modules are started in sequence according to preset time intervals.

8. The method according to claim 6, characterized in that Also includes: When the light intensity is less than a second preset light intensity threshold and the sum of the output powers of the plurality of DC collection modules is less than a second preset power threshold, the plurality of DC collection modules and the AC inverter module are sequentially shut down at preset time intervals.

9. The method according to any one of claims 6 to 8, characterized in that The DC collection module includes a plurality of collection submodules, each of which includes a maximum power point tracking module; the method further includes: In the case that the electrical signal output by the AC inverter module drops abnormally, the maximum power point tracking module is used to exit the maximum power point tracking mode, and the power compensation module is used to switch to the reactive power injection mode.

10. The method according to claim 9, characterized in that Also includes: When the electrical signal output by the AC inverter module increases abnormally, obtaining the power value output by the maximum power point tracking module; When the power value output by the maximum power point tracking module is greater than a third preset power threshold, the maximum power point tracking module is used to output a target power value, the target power value is less than or equal to the third preset power threshold, and the power compensation module is used to switch to a reactive absorption mode.

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