New energy direct current collection system, control system, control method and medium

Abstract

The invention relates to the technical field of new energy direct current collection, in particular to a new energy direct current collection system, a control system, a control method and a medium, the new energy direct current collection system comprises a direct current collection part which adopts at least two topology types of direct current transformers to collect and transmit new energy power to a medium-voltage direct current bus from a low-voltage side; and the direct-current transmission part is connected with the medium-voltage direct-current bus, inverts the direct-current medium voltage into alternating-current high voltage through a hybrid commutation converter HCC based on the IGCT and transmits the alternating-current high voltage out. According to the invention, the DC transformers of different topology types are applied to the new energy DC collection system, so that on one hand, the scene of large-scale new energy collection and transmission can be satisfied; on the other hand, the engineering performance of transformers with various topological structures is actually compared in an approximate working condition, and a supporting material can be provided for a next-step large-scale operation scheme; and the problem of commutation failure is solved by adopting a hybrid commutation technology.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy direct current collection, and in particular to a new energy direct current collection system, a control system, a control method and a medium. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Compared with traditional thermal power, hydropower and new energy bases, the Shagohuang New Energy Base has the following characteristics: 1) Wind power, photovoltaic and other new energy sources occupy the main position (capacity share > 80%), and the randomness, intermittency and volatility of new energy output lead to extremely high uncertainty in the base's power generation; 2) The Shagohuang area lacks water sources, the construction cost of thermal power is high, the proportion of synchronous units in the base is low, and the grid architecture is relatively weak; 3) The local living conditions are harsh, the local load is extremely small, and the base is far away from the load center and the main grid. Almost all electricity must be transmitted over large distances through ultra-high voltage lines.

[0004] Traditional new energy is connected to the grid by AC aggregation. After AC aggregation, there are two ways of sending out, one is AC sending and the other is DC sending. Qinghai Power Grid uses DC sending, and the specific method is LCC-HVDC. The outstanding feature of this method of AC aggregation and AC sending is weak reactive power regulation capability. The outstanding feature of this method of AC aggregation and DC sending is the need to maintain synchronization and stability. This topology is the main way of current new energy aggregation. Its advantages are low cost and simple operation, but at the same time, there are problems such as poor grid regulation capability, poor power quality and stability, and great impact of AC and DC system failures on new energy power stations.

[0005] In general, the networking solutions for traditional new energy bases have problems such as large investment in auxiliary support equipment, prominent new oscillation stability issues, and reliance on traditional synchronous power supply support. In addition, the existing networking solutions for new energy bases do not meet the needs of efficient and large-scale development of the Shagohuang new energy base, and there is an urgent need to develop new collection, networking, and external transmission technology solutions.

[0006] Renewable energy is collected through DC and integrated into the AC main grid at the sending end, and then sent to the receiving end together with conventional energy through LCC-HVDC. The advantages of this topology are: VSC has self-shutdown capability and can connect to passive systems, so it can be directly used for new energy power collection to provide stable and high-quality AC voltage for new energy power stations. DC collection is easy to form a multi-terminal system, which can give play to the temporal and spatial complementary characteristics of new energy to reduce output fluctuations, has stronger regulation capabilities, and has less impact on the sending-end power grid. DC collection isolates the power station from the AC grid, and there is no AC stability problem. The power quality of the collection system is higher, and AC and LCC-HVDC faults have less impact on new energy power stations. However, the disadvantage is that DC collection is currently more expensive and less economical.

[0007] At present, some new solutions have also emerged in the field of new energy DC collection. For example, Chinese patent document CN118412914A records a large-scale onshore new energy all-DC collection and transmission system, CN118054387A records a new energy DC collection and transmission system and its sending-end start-up method, and CN115603356A records a new energy DC collection and transmission system based on DC transformer and its control method. However, these solutions lack system solutions involving DC transformers with different topological structures on the one hand, and on the other hand, there is a risk of commutation failure. In view of the above defects, the present invention has made improvements. Summary of the invention

[0008] In order to overcome the shortcomings of the background technology, the present invention provides a new energy DC collection system, a control system, a control method and a medium. A variety of DC transformers with different topology types are applied in the new energy DC collection system. On the one hand, it can meet the scenarios of large-scale new energy collection and transmission; on the other hand, the engineering performance of transformers with various topological structures is actually compared under similar working conditions, which can provide support materials for the next large-scale operation plan; and the hybrid commutation technology is used to solve the problem of commutation failure.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] In a first aspect, a new energy direct current collection system is provided, the system comprising:

[0011] The DC collection part uses at least two types of DC transformers to collect and transmit the new energy power from the low-voltage side to the medium-voltage DC bus;

[0012] The DC transmission part is connected to the medium-voltage DC bus, and converts the DC medium voltage into AC high voltage through the IGCT-based hybrid commutation converter HCC before transmitting it.

[0013] Further,

[0014] All the DC transformers have the same capacity level, transformation ratio and transformation level.

[0015] Further,

[0016] The DC transformer is composed of a plurality of boost converter modules, and the high voltage sides of the boost converter modules are connected in series or in parallel;

[0017] Among the multiple DC transformers, at least one type of DC transformer has a number of series-connected boost converter modules, a number of parallel-connected modules, module device characteristics, or a combined topology between modules that are different from those of other types of DC transformers.

[0018] Further,

[0019] The output end of the DC transformer is connected to the medium voltage DC bus through two diodes, one positive and one negative.

[0020] Further,

[0021] The hybrid commutation converter HCC is equipped with a reactive power compensation device.

[0022] Further,

[0023] A rectifier power supply is connected between the AC bus and the medium voltage DC bus as an auxiliary power supply for the new energy DC collection system.

[0024] In a second aspect, a new energy DC collection control system is also provided, which is applied to the aforementioned new energy DC collection system, and the control system includes an upper coordination control layer and a lower local control layer;

[0025] The upper coordination control layer is used for upper control, including: receiving external dispatching operation mode and power instructions and performing corresponding actions, sending control instructions and control reference values ​​for equipment control to the lower local control layer, and performing normal start and stop control, AC and DC fault response control and operation mode switching of the new energy DC collection system;

[0026] The lower local control layer is used for lower distributed control, including executing HCC control strategy, SVG control strategy, LCC control strategy, DCT control strategy and MPPT control strategy.

[0027] In a third aspect, a new energy DC collection system operation control method is also provided, which is applied to the aforementioned new energy DC collection control system, wherein the operation modes of the new energy DC collection system include a unidirectional power grid-connected mode, an SVG reactive mode, and an outage mode; the operation control method includes:

[0028] According to external dispatching control instructions and / or system operating conditions, the new energy DC collection control system controls the operating mode switching of the unidirectional power grid-connected mode, SVG reactive mode, and shutdown mode through the upper coordination control layer, and sends the control instructions and control reference values ​​corresponding to the operating mode to the lower local control layer when switching to any operating mode.

[0029] Further,

[0030] In the unidirectional power grid-connected mode, the control instructions and control reference values ​​are issued by the upper coordination control layer; the HCC works in a constant DC voltage control state, and the SVG matched with the HCC provides reactive power support; the DCT low-voltage side is under constant voltage control; the photovoltaic MPPT low-voltage side works in the MPPT mode, and tracks the optimal voltage operating point according to the active power instruction;

[0031] In the SVG reactive power mode, the new energy DC collection system does not transmit active power, but only participates in AC reactive power regulation; HCC, DCT, and MPPT are all in a locked state in this mode, and only the SVG matched with the HCC outputs reactive power;

[0032] In the shutdown mode, the HCC, DCT and MPPT in the new energy DC collection system are all in a shutdown state.

[0033] Based on the same inventive concept, the present invention also provides a computer-readable storage medium storing one or more programs, which, when executed, can implement the aforementioned new energy DC collection system operation control method.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. Applying a variety of DC transformers of different topology types in the new energy DC collection system can, on the one hand, meet the scenario of large-scale new energy collection and transmission; on the other hand, by actually comparing the engineering performance of transformers of various topologies under similar working conditions, it can provide support materials for the next large-scale operation plan;

[0036] 2. The hybrid commutation technology is used in the new energy DC collection system to solve the problem of commutation failure;

[0037] 3. Based on the new energy DC collection system, a new energy DC collection control system was built, and the corresponding operation control method was provided, which can implement the corresponding control strategy well, thereby ensuring the normal operation of various equipment under various working conditions.

[0038] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings.

[0039] The present invention will be further described below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0041] Figure 1 A topological diagram of a new energy DC collection system according to an embodiment of the present invention;

[0042] Figure 2 This is a schematic diagram of the control architecture of a new energy DC collection control system according to an embodiment of the present invention;

[0043] Figure 3 A schematic diagram of three operating modes and switching relationships of an embodiment of the present invention;

[0044] Figure 4 The figure is a schematic diagram of protection zones of a new energy DC collection protection system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages of the implementation of the present invention clearer, the technical solution in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] like Figures 1 to 4 As shown, an embodiment of the present invention discloses a new energy DC collection system, the system comprising:

[0047] The DC collection part uses at least two types of DC transformers to collect and transmit the new energy power from the low-voltage side to the medium-voltage DC bus;

[0048] The DC transmission part is connected to the medium-voltage DC bus, and converts the DC medium voltage into AC high voltage through the IGCT-based hybrid commutation converter HCC before transmitting it.

[0049] In the above technical solution, the DC collection part is used to collect the new energy power from the low-voltage side and transmit it to the medium-voltage DC bus, and the collection adopts at least two topology types of DC transformers for boosting; the DC transmission part is used to invert the collected new energy power from DC medium voltage to AC high voltage through a hybrid commutation converter HCC and then send it out.

[0050] The embodiment of the present invention proposes a full DC solution of DC collection and DC transmission. The outlet of the new energy power generation equipment (the photovoltaic module in this embodiment) is connected to a DC transformer of different topological types for boosting. The DC boost converter (DC / DC converter, DC / DC transformer, referred to as DCT) is the most important power conversion device in the DC collection system. Its core function is to achieve the voltage level increase from LVDC to MVDC. At the same time, according to the different collection system architecture and the converter's own topology, it can also have the functions of MPPT control and multi-branch energy collection.

[0051] The aggregation of this embodiment uses at least two topology types of DC transformers for boosting. In order to achieve high-gain, high-efficiency DC power conversion and other supporting functions, different DC boost converter topology solutions can be selected according to the aggregation system architecture, actual system parameters, and operating conditions.

[0052] The above technical solution applies DC transformers of various topology types in the new energy DC collection system. On the one hand, it can meet the scenarios of large-scale new energy collection and transmission; on the other hand, it can actually compare the engineering performance of transformers of various topologies under similar working conditions, which can provide support materials for the next large-scale operation plan; and the hybrid commutation technology is used to solve the problem of commutation failure.

[0053] In this embodiment, a large-scale photovoltaic power station completes the boosting and collection through a high-power, high-voltage ratio DC / DC converter, and then transmits it over long distances through a DC line to form a full DC collection networking mode, which can effectively avoid problems such as reactive support and low-frequency oscillation that occur during the AC boosting, collection and transmission process. In addition, it has few equipment, low losses and high efficiency, which has great advantages and is an important development trend in the future.

[0054] The above-mentioned new energy DC collection system will be further explained below.

[0055] The overall topological structure of the new energy DC collection system in this embodiment is as follows: Figure 1As shown, the source side is a photovoltaic new energy station. The collection system uses a variety of topological types of DC transformers to step up the voltage and transmit it to the receiving end (i.e., the DC transmission part) through a DC line (i.e., a medium-voltage DC bus). The receiving end is inverted into AC high voltage (AC 35kV in this embodiment) through a converter (a hybrid commutation converter HCC is used in this embodiment, and this article also writes it as an HCC converter) and then sent out.

[0056] In this embodiment, the medium voltage DC bus MVDC is ±15 kV. In practical applications, different voltage levels can be selected according to DC transmission distance, capacity, equipment cost, etc., without affecting the system topology.

[0057] In this embodiment, the source side of the DC collection part is a photovoltaic new energy station. Under different DC collection system architectures, the DC boost converter should have the necessary performance characteristics corresponding thereto to meet the needs of system operation. The present invention proposes to apply a variety of different transformer topologies in the system, perform actual operations, and comprehensively compare the advantages and disadvantages.

[0058] In this embodiment, all the DC transformers described have the same external characteristics such as capacity level, transformation ratio, and transformation level. In specific implementation, the low-voltage side voltage, high-voltage side voltage, transformation ratio, capacity level, and transformation level of each DC transformer are the same. Furthermore, the DC transformer is composed of multiple boost converter modules, and the high-voltage side of each module is connected in series or in parallel; among the multiple DC transformers, at least one type of DC transformer has a boost converter module series level, or a module parallel level, or a module device characteristic, or a module combination topology that is different from other types of DC transformers.

[0059] Specifically, the DC collection part of the preferred embodiment of the present invention includes three types of DC transformers of topological types, namely, the first transformer topological structure (i.e., scheme 1), the first transformer topological structure (i.e., scheme 2) and the first transformer topological structure (i.e., scheme 3). The topological diagrams of each scheme are shown in the attached Figure 1 As shown, the parameters of each solution are shown in Table 1 below. In specific implementation, the topology type of the DC transformer in the DC collection part may not be limited to the three types of this preferred embodiment. The more topology types are used, the larger the comparison range is. Therefore, the actual comparison topology type and quantity can be further selected according to actual needs. For low-voltage side switching devices, IGBT is more suitable for projects with smaller installed capacity, and IGCT is more suitable for large-capacity and large-scale projects.

[0060] Different transformer topologies have different advantages and disadvantages. Previous comparisons in this field have focused more on technical analysis. The solution of the present invention and the supporting demonstration projects use a variety of topologies (three in this embodiment) to provide technical endorsement and support for the performance of the topology through engineering performance, so that the project can conduct more extensive experiments on the one hand, and on the other hand, it can conduct a comprehensive comparison of different topologies, providing engineering experience guidance for the next step of technical development and solution research of DC technology.

[0061] Table 1 DC transformers of different topology types

[0062]

[0063] The receiving end of the embodiment of the present invention adopts a hybrid commutation converter HCC device based on IGCT. While retaining the basic topology of the thyristor commutation valve, the HCC uses IGCT devices to replace the thyristors in the original LCC commutation bridge arm, forming an HCC converter with active controllable shutdown capability. On the basis of retaining the advantages of the original LCC converter in terms of cost and loss, the controllable shutdown capability is added to it, further improving the transmission performance of the LCC DC. The LCC and the hybrid commutation converter HCC based on IGCT can be further described in the prior art, which will not be elaborated here.

[0064] In some embodiments, the output end of the DC transformer is connected to the medium voltage DC bus through two diodes, one positive and one negative. Figure 1 As shown, the embodiment of the present invention has five collection units, and the function of the diode is that when there is an internal fault in the collection side unit, other units do not inject direct current, that is, the fault does not affect other units.

[0065] In some embodiments, the HCC converter is configured with a 30Mvar reactive power compensation device. The above configuration needs to take into account the grid voltage fluctuation, and the reactive power demand generated by HCC and LCC on the AC side during operation; in addition, the harmonic compensation demand for characteristic subharmonics generated on the AC side is also considered.

[0066] In some embodiments, the reactive equipment (i.e., the reactive compensation device corresponding to the aforementioned HCC converter, SVG is used in this embodiment) and the electric energy are connected to the 35kV distribution cabinet of the booster station through a 35kV line. The electric energy here refers to the energy generated by the photovoltaic module, which is inverted into alternating current by the HCC equipment. The statement here means that this part of the new energy power generation and the reactive output of SVG are connected to the booster station through a 35kV line. The 35kV line specifically refers to a 3-core AC cable, one end of which is connected to the HCC grid point, and the other end is connected to the 35kV distribution cabinet in the booster station.

[0067] In some embodiments, a rectifier power supply is connected between the AC bus and the medium-voltage DC bus, and a rectifier is drawn from the AC bus through the rectifier power supply as an auxiliary power supply for the new energy DC collection system. In this embodiment, a rectifier is drawn from the 35kV AC as an auxiliary power supply for the new energy DC collection system, that is, a rectifier power supply is drawn from the 35kV AC bus and connected to the medium-voltage DC bus of the system, as an auxiliary power supply for the system, to support stable operation of the system. The operation process of the auxiliary power supply is divided into 2 step controls. Every morning, the equipment starts up at full power of 5MW, and after the light intensity reaches 50%, it is changed to 2.5MW power operation. When the light intensity meets the full power operation of the equipment, it stops. The rectifier power supply of this embodiment is preferably a thyristor rectifier power supply, which can be well used as an auxiliary power supply and support the stable operation of the system.

[0068] In a second aspect, an embodiment of the present invention further discloses a new energy DC collection control system, which is applied to the aforementioned new energy DC collection system, and the control system includes an upper coordination control layer and a lower local control layer;

[0069] The upper coordination control layer is used for upper control, including: receiving external dispatching operation mode and power instructions and performing corresponding actions (i.e. receiving dispatching mode and instructions), sending control instructions and control reference values ​​for equipment control (i.e. equipment control) to the lower local control layer, and performing normal start and stop control, AC and DC fault response control and operation mode switching of the new energy DC collection system;

[0070] The lower local control layer is used for lower decentralized control, including the execution of HCC control strategy, SVG control strategy, LCC control strategy, DCT control strategy and MPPT control strategy. The execution of each control strategy can be carried out according to the actual control requirements.

[0071] Considering the characteristics of new energy power generation, the present invention designs a new type of regulation and stable control method suitable for the Shagohuang new energy base, and realizes it through the above-mentioned control system. Among them, in the medium and long-term power balance, the strong volatility of new energy and the constraints of external transmission capacity are considered to achieve the best economy of the whole life cycle; in the short-term power balance, the constraints of transient performance (voltage, frequency, non-power frequency) are considered to achieve the coordination of multiple heterogeneous equipment and balanced sharing of unbalanced power after disturbance, comprehensively resolve the stability risks of all working conditions and all aspects, and ensure equipment safety and system stability.

[0072] The overall control architecture of the new energy DC collection control system in this embodiment is as follows: Figure 2As shown in the figure, the control system scheme is divided into two levels according to the control scope and control function, namely the upper coordination control layer and the lower local control layer. Among them: the upper coordination control layer is the upper control, which determines the external dispatching operation mode and power command (active and reactive command reference values) accepted by the new energy DC collection system according to the external dispatching requirements, and sends control commands and control reference values ​​to each key device of the local equipment control layer (i.e. the lower local control layer), and at the same time the control system realizes smooth switching between operation modes and coordinated processing when the AC system fails; the lower local control layer is the lower decentralized control, including the execution of HCC control strategy, DCT control strategy and photovoltaic BOOST control strategy, and each key device such as HCC, DCT, MPPT and so on controls itself according to its own principles and characteristics.

[0073] The dispatching control layer (i.e., external top-level dispatching) is located at the master station or dispatching center. It generates the system's operating mode instructions and their corresponding reference value instructions based on the real-time topology, real-time power flow, voltage and frequency information of the AC power grid and the grid dispatching requirements.

[0074] The active power connected to the grid is controlled by the DC combiner boxes that are distributed locally. When the system operates under the maximum power grid-connected condition, all DC combiner boxes with MPPT function in the system operate in the maximum power tracking mode. The active power connected to the grid is related to factors such as lighting conditions and temperature. When the system operates under the fixed active power grid-connected condition, all DC combiner boxes in the system operate in the fixed DC voltage mode, and a closed-loop control is formed between the DC voltage reference value and the active power reference value.

[0075] The reactive power connected to the grid is controlled by the HCC converter valve. The HCC converter valve can control the output of active and reactive power, as well as the output of inductive or capacitive reactive power, to support voltage stability and ensure power quality.

[0076] The scheme of the present invention is a complete electrical system, which includes both the primary equipment system topology and the secondary control and operation mode. This part (i.e. the active power control and reactive power control of the above-mentioned access to the power grid) is the control scheme of each device in the control mode of the system of this scheme - hierarchical control - local layer (i.e. the lower local control layer).

[0077] In a third aspect, an embodiment of the present invention further discloses an operation control method of a new energy DC collection system, which is applied to the aforementioned new energy DC collection control system, wherein the operation modes of the new energy DC collection system include a unidirectional power grid-connected mode, an SVG reactive mode, and an outage mode; the operation control method includes:

[0078] According to external dispatching control instructions and / or system operating conditions, the new energy DC collection control system controls the operating mode switching of the unidirectional power grid-connected mode, SVG reactive mode, and shutdown mode through the upper coordination control layer, and sends the control instructions and control reference values ​​corresponding to the operating mode to the lower local control layer when switching to any operating mode.

[0079] This embodiment proposes mode management (i.e., a new energy DC collection system operation control method) in combination with the system topology (i.e., the new energy DC collection system topology). The targeted nature of the combination is mainly reflected in the reactive operation mode (i.e., the SVG reactive mode), which can only output reactive power. This mode has the characteristic of being able to output reactive power based on HCC.

[0080] The new energy DC collection system of this embodiment mainly includes three operating modes: unidirectional power grid-connected mode, SVG reactive mode, and shutdown mode. The new energy DC collection control system controls the system operation mode according to external dispatching control instructions and / or system operation conditions. The system operation mode control includes: unidirectional power grid-connected mode, SVG reactive mode, shutdown mode switching and mode instruction issuance. Under different system operation conditions and / or external control instructions, the switching relationship between the three operation modes of the system is as follows: Figure 3 shown.

[0081] The three operating modes are further explained below.

[0082] Unidirectional power grid-connected mode: HCC works in a constant DC voltage control state, and the SVG supporting HCC provides reactive power support; the DCT low-voltage side has constant voltage control; the photovoltaic MPPT low-voltage side works in the MPPT mode, and tracks the optimal voltage operating point according to the active power instruction. The coordination control layer sends down each control instruction value (that is, the control instructions and control reference values ​​are sent through the upper coordination control layer). The unidirectional power grid-connected mode is the most common operating mode of the photovoltaic DC collection system. The dispatcher can directly send power instructions to the photovoltaic MPPT, or it can work in the MPPT (maximum power point tracking) mode, with HCC controlling the DC voltage and SVG providing reactive power support. The unidirectional power of this embodiment refers to the unidirectional flow of electric energy, from the renewable energy power generation side to the grid connection point.

[0083] SVG reactive power mode: The new energy DC collection system does not transmit active power, but only participates in AC reactive power regulation; HCC, DCT, and MPPT are all in a locked state in this mode, and only the SVG matched with HCC outputs reactive power. In SVG reactive power mode, the photovoltaic collection system does not send active power, but only participates in AC reactive power regulation. The SVG device can accept dispatching instructions, and its reactive power reference value Qref is also given by the top-level control (i.e., external top-level dispatching).

[0084] Shutdown mode: In this mode, the HCC, DCT and MPPT in the new energy DC collection system are all in shutdown state. When the HCC and DCT are shut down, the isolation switch is pulled open and the ground switch is grounded.

[0085] When receiving a dispatch control instruction or a specific event occurs, the system coordination controller should take corresponding actions.

[0086] In this embodiment, normal start and stop, normal operation mode switching and fault response are the three major control functions of the upper coordination control layer; through these control functions, the DC collection system is defined in a specific operating state, when it receives a specific dispatching control instruction or a specific event occurs, the system coordination controller should perform the mode switching action. The switching relationship between the three operating modes is as follows: Figure 3 In the above-mentioned specific events, such as a fault, or a sudden rainy day causing the light intensity to not meet the system operation, the system will switch from grid-connected operation to shutdown, and then resume after the event, i.e., the "fault response" in the figure. In this embodiment, the occurrence of a specific event will affect the system operating conditions.

[0087] ① / ②Normal start-stop control: describes the normal start-stop control of the outage mode and SVG reactive mode, as well as the normal start-stop control of the outage mode and grid-connected operation mode.

[0088] ③ Normal operation mode switching: describes the switching strategy of the system's operation modes other than the shutdown mode under normal working conditions. It is the main coordination control function for connecting various control instructions of the dispatching control layer.

[0089] ④⑤⑥ Fault response: AC system temporary fault response, the system has fault ride-through capability, all equipment in the DC collection system should be able to withstand overvoltage and overcurrent stress during the ride-through period and no lockout protection occurs; DC system fault or AC system serious fault response, when a fault occurs at various locations inside the DC collection system or a serious fault occurs in the AC system and is outside the high and low ride-through capability or the AC interconnection line is broken or the interconnection line is tripped, it should have emergency response capability, that is, lock out all equipment in the DC system.

[0090] In addition, an embodiment of the present invention also discloses a new energy DC collection protection system, which is applied to the aforementioned new energy DC collection system, and the protection system includes a first protection zone, a second protection zone, a third protection zone and a fourth protection zone; the first protection zone is used to protect the new energy power generation equipment in the DC collection part; the second protection zone is used to protect the DC transformer equipment in the DC collection part; the third protection zone is used to protect the medium voltage DC bus; the fourth protection zone is used to protect the DC transmission part.

[0091] According to the principle of protection area division and the protected objects in the system, the protection area of ​​the new energy DC collection system (i.e., photovoltaic DC collection system) in this embodiment is divided as follows: Figure 4 The entire protection system is divided into photovoltaic equipment protection zone, DC transformer protection zone, DC line protection zone, and HCC converter valve protection zone (including connecting transformer), which correspond to the first protection zone, the second protection zone, the third protection zone, and the fourth protection zone mentioned above respectively.

[0092] The present invention improves and optimizes the overall system topology of the new energy DC collection control system. The source side is a photovoltaic new energy station. The DC transformers using various topologies are used to collect and step up the voltage and then transmit it to the receiving end through a DC line. The receiving end is inverted into 35kV AC through a hybrid commutation technology and then sent out. In addition, a rectifier is drawn from the 35kV AC as an auxiliary power supply for the system. A control and protection strategy corresponding to the above system is designed, and the control and protection logic of the entire system is constructed through "two-layer control, four-zone protection" to ensure the normal operation of various equipment under various working conditions.

[0093] Aiming at the industrial needs and project characteristics of the development of the Shagohuang large base, and the various restrictions on the traditional large-scale new energy networking mode, this invention proposes a new DC collection-DC transmission solution, and configures 3 different DC transformer topology solutions on the collection side, adopts the HCC hybrid converter valve solution based on IGCT on the receiving end, analyzes the operating characteristics of different solutions, and proposes a DC power grid control and protection strategy for this solution. This invention aims to solve the problem that the traditional networking mode does not meet the needs of efficient and large-scale development of the Shagohuang large base, which is not only conducive to solving the difficulties of the industrial development plan of the Shagohuang large base, but also proposes a more advantageous implementation idea for the national new energy development process plan.

[0094] Based on the same inventive concept, the present invention also provides a computer-readable storage medium storing one or more programs, which, when executed, can implement the aforementioned new energy DC collection system operation control method.

[0095] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0096] Parts not involved in the above embodiments are the same as the prior art or can be implemented by using the prior art, and will not be further described here.

[0097] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A new energy DC collection system, characterized in that: The system comprises: The DC collection part uses at least two types of DC transformers to collect and transmit the new energy power from the low-voltage side to the medium-voltage DC bus; The DC transmission part is connected to the medium-voltage DC bus, and converts the DC medium voltage into AC high voltage through the IGCT-based hybrid commutation converter HCC before transmitting it.

2. A new energy DC collection system according to claim 1, characterized in that: All the DC transformers have the same capacity level, transformation ratio and transformation level.

3. A new energy DC collection system according to claim 2, characterized in that: The DC transformer is composed of a plurality of boost converter modules, and the high voltage sides of the boost converter modules are connected in series or in parallel; Among the multiple DC transformers, at least one type of DC transformer has a number of series-connected boost converter modules, a number of parallel-connected modules, module device characteristics, or a combined topology between modules that are different from those of other types of DC transformers.

4. A new energy DC collection system according to claim 1, characterized in that: The output end of the DC transformer is connected to the medium voltage DC bus through two diodes, one positive and one negative.

5. A new energy DC collection system according to claim 1, characterized in that: The hybrid commutation converter HCC is equipped with a reactive power compensation device.

6. A new energy DC collection system according to claim 1, characterized in that: A rectifier power supply is connected between the AC bus and the medium voltage DC bus as an auxiliary power supply for the new energy DC collection system.

7. A new energy DC collection control system, applied to the new energy DC collection system according to any one of claims 1 to 6, characterized in that: The control system comprises an upper coordination control layer and a lower local control layer; The upper coordination control layer is used for upper control, including: receiving external dispatching operation mode and power instructions and performing corresponding actions, sending control instructions and control reference values ​​for equipment control to the lower local control layer, and performing normal start and stop control, AC and DC fault response control and operation mode switching of the new energy DC collection system; The lower local control layer is used for lower distributed control, including executing HCC control strategy, SVG control strategy, LCC control strategy, DCT control strategy and MPPT control strategy.

8. A method for controlling the operation of a new energy DC collection system, applied to the new energy DC collection control system according to claim 7, characterized in that: The operation modes of the new energy DC collection system include a unidirectional power grid-connected mode, an SVG reactive mode and an outage mode; the operation control method includes: According to external dispatching control instructions and / or system operating conditions, the new energy DC collection control system controls the operating mode switching of the unidirectional power grid-connected mode, SVG reactive mode, and shutdown mode through the upper coordination control layer, and sends the control instructions and control reference values ​​corresponding to the operating mode to the lower local control layer when switching to any operating mode.

9. The operation control method of a new energy DC collection system according to claim 8 is characterized in that: In the unidirectional power grid-connected mode, the control instructions and control reference values ​​are issued by the upper coordination control layer; the HCC works in a constant DC voltage control state, and the SVG matched with the HCC provides reactive power support; the DCT low-voltage side is under constant voltage control; the photovoltaic MPPT low-voltage side works in the MPPT mode, and tracks the optimal voltage operating point according to the active power instruction; In the SVG reactive power mode, the new energy DC collection system does not transmit active power, but only participates in AC reactive power regulation; HCC, DCT, and MPPT are all in a locked state in this mode, and only the SVG matched with the HCC outputs reactive power; In the shutdown mode, the HCC, DCT and MPPT in the new energy DC collection system are all in a shutdown state.

10. A computer-readable storage medium storing one or more programs, characterized in that: When the one or more programs are executed, the new energy DC collection system operation control method described in any one of claims 8-9 can be implemented.

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