New energy via-network LCC-HVDC sending-out method and new energy via-network LCC-HVDC sending-out system

Abstract

The invention discloses a new energy network construction type LCC-HVDC sending-out method and system, and relates to the technical field of direct current transmission, and the method comprises the steps: monitoring the operation state of a receiving end power grid in real time, and calculating the frequency deviation and direct current voltage deviation of the receiving end power grid according to the operation state; coupling the frequency deviation into the direct-current voltage deviation, generating a composite signal, inputting the composite signal into a receiving-end PI controller, carrying out amplitude limiting processing on the output of the receiving-end PI controller by taking a preset extinction angle range as a boundary, generating an extinction angle control instruction, driving and adjusting the direct-current voltage of the receiving end, and sending the direct-current voltage to a sending-end power grid; compensating the adjusted receiving end DC voltage by using the DC line parameters and restoring a sending end frequency reference value, and then injecting the reference value into the networking SVG for control; the capacitor voltage of the direct-current link is synchronously monitored, and when the monitoring result meets the preset condition, a power rebalance mechanism is triggered and inertia support is provided, so that the reliability of new energy transmission is improved.

Description

Technical Field

[0001] This invention relates to the field of DC power transmission technology, and in particular to a new energy grid-type LCC-HVDC transmission method and system. Background Technology

[0002] In long-distance power transmission and grid connection systems of large-scale new energy bases, conventional high-voltage AC (HVAC) technology faces limitations in transmission distance and capacity due to the capacitance effect of AC cables. Therefore, high-voltage DC solutions, represented by conventional DC transmission (LCC-HVDC), have been widely used.

[0003] However, when these traditional methods are applied to centralized transmission of new energy sources, they cannot provide stable voltage and frequency support for the sending-end LCC converter station in the face of weak grid areas such as the Shagohuang New Energy Base, which seriously limits the efficient and reliable grid connection of large-scale wind power, photovoltaic and other new energy sources.

[0004] Therefore, how to effectively transmit new energy sources and ensure the stable operation of the power transmission system has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] This invention provides a method and system for transmitting new energy through a grid-connected LCC-HVDC, which solves the problem of how to restore and balance the frequency at the transmitting and receiving ends by coordinating grid-connected SVG and LCC-HVDC, thereby improving the operational reliability of the power transmission system.

[0006] To address the aforementioned technical problems, embodiments of the present invention provide a method for transmitting renewable energy through a grid-connected LCC-HVDC, applied to the receiving-end power grid, comprising: The operating status of the receiving-end power grid is monitored in real time, and the frequency deviation and DC voltage deviation of the receiving-end power grid are calculated based on the operating status. The frequency deviation is coupled to the DC voltage deviation to generate a composite signal, which is then input to the receiving-end PI controller for proportional-integral calculation. Using a preset arc-extinguishing angle range as the boundary, the output of the receiving-end PI controller is limited to generate an arc-extinguishing angle control command; In response to the arc extinction angle control command, the receiving-end DC voltage is regulated and sent to the sending-end power grid.

[0007] Furthermore, the frequency deviation is coupled to the DC voltage deviation to generate a composite signal. The voltage compensation amount is obtained by multiplying the frequency deviation with a preset droop coefficient. The voltage compensation amount is superimposed on the DC voltage deviation to generate the composite signal.

[0008] This invention provides a method for transmitting renewable energy-based LCC-HVDC power through a grid, applicable to the sending-end power grid, comprising: The adjusted receiving-end DC voltage is received, and the adjusted receiving-end DC voltage is compensated using DC line parameters to obtain a voltage estimate. Based on the voltage estimate, the sending-end frequency reference value is reconstructed, and the sending-end frequency reference value is injected into the grid-type SVG for hierarchical control. The DC link capacitor voltage of the grid-type SVG is monitored synchronously. When the monitoring result meets the preset conditions, the power rebalancing mechanism is triggered. At the same time, the converter is triggered to generate a control signal based on the monitoring result, and the charging and discharging power of the supercapacitor is adjusted by the control signal.

[0009] Furthermore, the step of injecting the sending-end frequency reference value into the network-type SVG for hierarchical control includes: The sending-end frequency reference value is injected into the outer control loop of the network-type SVG. Based on the sending-end frequency reference value and the rated voltage amplitude, a voltage reference command is generated and sent to the inner control loop of the network-type SVG. In response to the voltage reference command, voltage and current dual closed-loop control is performed in the inner control loop to generate a target AC voltage on the sending-end AC bus.

[0010] Furthermore, the process of obtaining the DC line parameters includes: With the goal of minimizing the error function output, the equivalent resistance and inductance of the DC line are identified online using the least squares method to obtain the parameters of the DC line.

[0011] Furthermore, the power rebalancing mechanism triggered when the monitoring results meet preset conditions includes: When the voltage of the DC link capacitor is detected to exceed a preset first threshold, a DC current limiting operation is triggered. When the DC link capacitor voltage is detected to drop to a preset second threshold, a power transmission recovery operation is performed under a preset voltage slope limit.

[0012] Another embodiment of the present invention provides a new energy grid-connected LCC-HVDC transmission system, comprising: a base-side power generation module, an LCC-HVDC module, and a grid-connected SVG applied to the above-mentioned new energy grid-connected LCC-HVDC transmission method; The base-side power generation module includes wind turbine units, and each wind turbine unit is equipped with a first converter, a converter group and a wind turbine generator connected to a first supercapacitor. The LCC-HVDC module includes a sending-end converter station and a receiving-end converter station that are interconnected; one side of the sending-end converter station is connected to the base-side AC bus of the base-side power generation module. The grid-type SVG is connected in parallel to the AC bus on the base side, and is used to provide grid-connected voltage to the base-side power generation module and commutation voltage to the sending-end converter station.

[0013] Furthermore, the base-side power generation module also includes a photovoltaic generator set, which includes a photovoltaic array, a second converter connected to the second supercapacitor, and a grid-connected inverter.

[0014] Furthermore, the converter group includes: a machine-side converter and a grid-side converter; The machine-side converter integrates a rotor magnetic field orientation vector algorithm, and the grid-side converter integrates a grid voltage orientation vector algorithm.

[0015] Furthermore, the first converter is a bidirectional DC / DC converter.

[0016] Compared with the prior art, the beneficial effects of the embodiments of the present invention are at least one of the following: This invention superimposes the frequency deviation generated at the receiving end onto the DC voltage deviation, and drives the DC voltage adjustment after PI control and arc extinction angle limiting, thus achieving accurate transmission of frequency information at the receiving end without communication. At the sending end, DC line parameters are used to compensate for the DC voltage and current at the sending end, improving the accuracy of frequency restoration at the receiving end. Using the restoration result as a reference, the sending end uses a grid-type SVG to perform inner and outer loop control, constructing a stable sending-end power grid and ensuring the stable operation of the transmission system. By monitoring the DC link capacitor voltage of the grid-type SVG, power rebalancing and inertia support are triggered when limits are exceeded, which can effectively cope with fault fluctuations and achieve smooth reconnection to the grid, improving the reliability of long-distance transmission of new energy. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of a power transmission method applied to a receiving-end power grid in one embodiment of the present invention; Figure 2 This is a schematic flowchart of a power transmission method applied to a power grid at the sending end in one embodiment of the present invention; Figure 3 This invention provides a schematic diagram of a new energy grid-type LCC-HVDC transmission system. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] In the description of this application, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," "third," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0020] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. The terms "vertical," "horizontal," "left," "right," "upper," "lower," and similar expressions used herein are for illustrative purposes only and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0021] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the invention. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0022] One embodiment of the present invention provides a method for transmitting renewable energy through a grid-connected LCC-HVDC power grid, applied to the receiving-end power grid. For details, please refer to [link to relevant documentation]. Figure 1 , Figure 1 The diagram shown is a schematic flowchart of a power transmission method applied to a receiving-end power grid according to one embodiment of the present invention, including the following steps: S11~S12: Monitor the operating status of the receiving-end power grid in real time, calculate the frequency deviation and DC voltage deviation of the receiving-end power grid based on the operating status, couple the frequency deviation into the DC voltage deviation to generate a composite signal and input it to the receiving-end PI controller for proportional-integral calculation.

[0023] It should be understood that this embodiment designs a transmission mechanism based on LCC-HVDC (grid-commutated converter-high voltage direct current transmission system) + sending-end GFM-SVG (grid-type static var generator / grid-type SVG). In this embodiment, the receiving end is located on the receiving side of the DC transmission system, responsible for converting DC power into AC power and integrating it into the receiving-end grid. It also maps the frequency deviation of the receiving-end grid onto the DC voltage through DC voltage / frequency droop control, thus realizing frequency information transmission. Specifically, the operating status of the receiving-end grid, including frequency and DC voltage status, is monitored in real time, and the DC side voltage and frequency measurements of the receiving-end LCC are obtained. When events such as increased load occur in the receiving-end grid, frequency deviation will occur. These two measurements are compared with their corresponding rated values ​​to obtain two core deviation quantities: frequency deviation and DC voltage deviation.

[0024] Next, signal coupling is performed. Specifically, the frequency deviation is multiplied by a preset droop coefficient to obtain the voltage compensation amount, which is then added to the DC voltage deviation to generate a composite signal.

[0025] This operation actually utilizes DC voltage / frequency droop control, that is, the droop coefficient is the DC voltage / frequency droop coefficient. When superimposed, it creates a dual signal that reflects voltage and frequency changes, providing a reliable signal source for subsequent voltage regulation at the receiving end and restoration at the sending end.

[0026] S13~S14, using the preset arc extinction angle range as the boundary, the output of the receiving end PI controller is limited to generate an arc extinction angle control command. In response to the arc extinction angle control command, the receiving end DC voltage is adjusted and sent to the sending end power grid.

[0027] This step is the voltage regulation process at the receiving end. It should be understood that after the composite signal is input into the corresponding PI controller at the receiving end, the PI controller will output an "angle control signal" through proportional-integral calculation. This "angle control signal" can be used to drive the adjustment of the arc extinction angle, and the change in the arc extinction angle will directly cause a change in the DC voltage at the receiving end. Specifically, to ensure the safe operation of the transmission system and prevent commutation failure, the output of the receiving end PI controller will be strictly limited within a preset safe range for the arc extinction angle, such as 8° to 30°, during the amplitude limiting process. The final generated arc extinction angle control command is expressed by the following formula: in, γ The extinction angle signal represents the receiving end LCC, and the applied boundary conditions are: γ ∈[ γ min , γ max ], γ max / γ min Indicates the maximum arc extinction angle / minimum arc extinction angle; k pv and k iv These represent the proportional and integral parameters of the PI controller, respectively. s Represents the complex frequency variable in the Laplace domain; u dci0 and u dci These represent the rated and measured values ​​of the DC side voltage of the receiving-end LCC, respectively. f i and f 0 These represent the measured frequency value and the rated frequency value of the receiving-end power grid, respectively. K dc This represents the DC voltage / frequency droop factor.

[0028] In this embodiment, the receiving-end LCC includes two main components: a DC voltage outer loop and an arc extinction angle generator. The DC voltage outer loop uses a PI regulator, and the input is ( u dci0 - u dci That is, the DC voltage deviation value, which is output and then superimposed on the frequency droop term after being limited, to form an arc extinction angle control command carrying the arc extinction angle adjustment amount.

[0029] After adjusting the arc extinction angle, the receiving-end DC voltage changes accordingly. At this time, the frequency deviation of the receiving-end grid is linearly mapped and carried in the change of the receiving-end DC voltage, and propagates to the sending-end grid along with the DC current through the DC line. The purpose of these operations at the receiving end is to complete the transmission of frequency information without communication, providing a physical basis for the sending end to sense frequency disturbances at the receiving end and make supporting responses.

[0030] Based on this, one embodiment of the present invention also provides a method for transmitting new energy grid-connected LCC-HVDC, applied to the sending-end power grid. For details, please refer to [link to relevant documentation]. Figure 2 , Figure 2 The diagram shown is a schematic flowchart of a power transmission method applied to a sending-end power grid in one embodiment of the present invention, including the following steps: S21~S22 First, receive the adjusted DC voltage at the receiving end, and use the DC line parameters to compensate for the adjusted DC voltage at the receiving end to obtain a voltage estimate.

[0031] Specifically, at the sending end, the receiving end DC voltage and DC current transmitted from the DC line are collected in real time. Using known or online-identified DC line parameters, compensation calculations are performed on this receiving end DC voltage to estimate the receiving end DC voltage value, i.e., the voltage estimate, expressed by the following formula: In the formula, u dci2 This represents the estimated DC voltage at the receiving end after compensation. u dcr This indicates the real-time acquisition of the DC voltage measurement at the sending end. R dc Indicates the equivalent resistance of a DC line; L dc Indicates the equivalent inductance of a DC line; i dc This represents the real-time measured value of the DC line current.

[0032] Specifically, this embodiment will use voltage estimates. u dci2 Replace the receiving-end DC voltage, combined with the DC voltage / frequency droop factor K dc With respect to the rated value of the DC voltage at the sending end u dcr0 Restore the sending end frequency reference value, which is expressed as: in, f r-ref This represents the sending-end frequency reference value. By inputting it into GFM-SVG, the frequency of the receiving-end power grid can be mapped.

[0033] It is worth noting that, R dc , L dc Value deviation will lead to f r-ref To avoid estimation errors, this embodiment injects a low-amplitude disturbance signal (such as a non-characteristic harmonic, amplitude ≤ 1% pu, which does not affect normal transmission) into the DC side at the sending end. Simultaneously, the response at the injection point is measured. Based on this response, the goal is to minimize the error function output; in this embodiment, this means minimizing it within the sliding window of the error function. The equivalent resistance of the DC line is then identified online using the least squares method or the least squares method with a forgetting factor. R and inductor L The DC line parameters are obtained. For example, the error function is expressed by the following formula: In the formula, Represents the error function; u dcr ( k ) indicates the first k The measured DC voltage at the sending end of each sampling point; u dci ( k ) indicates the first k The measured DC voltage at the receiving end of each sampling point; i dc ( k ) indicates the first k DC line current measurement values ​​at each sampling point.

[0034] In some embodiments of the present invention, to avoid noise amplification, A second-order generalized differentiator or a two-point differential converter with hysteresis is employed. The DC line parameters are automatically updated when the line operating conditions change (such as switching between parallel / series converters or temperature changes).

[0035] Next, the sending-end frequency reference value is reconstructed based on the voltage estimate, and then injected into the network-type SVG for hierarchical control. In this embodiment, the network-type SVG adopts a voltage-current dual closed loop, with the outermost layer being a frequency / amplitude loop, and the inner layers including a voltage loop and a current loop.

[0036] Based on this architecture, the sending-end frequency reference value is injected into the outer control loop of the grid-type SVG. Using the sending-end frequency reference value and the rated voltage amplitude as a reference, a voltage reference command is generated and sent to the inner control loop of the grid-type SVG. In this loop, the frequency and voltage targets at the sending-end AC bus are set based on the sending-end frequency reference value and the rated voltage amplitude to drive the inner loop to adjust. Then, in the inner control loop, in response to the voltage reference command, voltage and current dual closed-loop control is executed to generate the target AC voltage on the sending-end AC bus and build a stable sending-end power grid.

[0037] S23. Synchronously monitor the DC link capacitor voltage of the grid-type SVG. When the monitoring result meets the preset conditions, trigger the power rebalancing mechanism. At the same time, trigger the converter to generate a control signal based on the monitoring result to adjust the charging and discharging power of the supercapacitor.

[0038] When dual-loop control is performed at the sending end, this embodiment will execute a rebalancing mechanism when a momentary power imbalance is detected between the sending and receiving ends. It should be understood that this power imbalance will impact the grid-type SVG, causing fluctuations (increases / decreases) in its DC link capacitor voltage.

[0039] Specifically, when the DC link capacitor voltage exceeds a preset first threshold, a DC current limiting operation is triggered; when the DC link capacitor voltage drops to a preset second threshold, a power transmission recovery operation is performed under a preset voltage slope limit. The first threshold can be set according to the rated voltage of the GFM-SVG DC link, such as 1725V, and the second threshold must be less than the first threshold, such as 1600V.

[0040] For example, when the receiving-end LCC commutation fails or the DC channel is blocked, the DC link capacitor voltage will fluctuate. At this time, the GFM-SVG enters energy absorption mode. The DC link capacitor voltage can be expressed as... V dc_svg When it rises to a preset first threshold in this state V h When it is determined that the short-term buffer is insufficient to cope with the continuous power imbalance, active protection measures are activated, such as reducing the power of the wind turbine generator and implementing current limiting mode for the LCC at the sending end.

[0041] When the fault at the receiving end is cleared, the DC link voltage drops and recovers to the second threshold. V l ( V h > V l Afterwards, for example, the wind turbine will increase its output power according to the preset voltage slope limit or power recovery slope, and the sending-end LCC will gradually restore the power transmission function according to the preset voltage slope limit. For the sending-end LCC, it can be set to restore the power transmission function gradually with a voltage slope not exceeding 100 kV / s.

[0042] Meanwhile, for example, in this embodiment, a momentary power imbalance occurs at the sending and receiving ends, i.e., a frequency deviation occurs. ( When representing the current frequency reference value, a control signal is generated using the converter, expressed as: in, u sc-ref This indicates the reference voltage value on the DC side of the supercapacitor; u sc0 This indicates the rated voltage on the DC side of the supercapacitor; gain. K iner With supercapacitor capacity C Rated capacity S n and target inertial time constant H Related. In engineering, it can be approximated by energy equivalence. To prevent SOC exceeding limits, the controller is set... u scThe upper / lower limits and soft limiting regions (such as 90% and 10%) are defined. When the limits are exceeded, the integration is paused and regression is performed using a slope-limited method.

[0043] This control signal is used to adjust the supercapacitor to provide rapid inertia support. In summary, this embodiment couples the receiving-end frequency deviation to the DC voltage through DC voltage / frequency droop control at the receiving end. The sending end uses built-in DC line parameters for online identification to accurately reconstruct the receiving-end frequency information and adjust the sending-end grid frequency accordingly. This allows for the detection of receiving-end frequency disturbances without the need for inter-station communication. Simultaneously, a DC / DC converter adjusts the charging and discharging power of the supercapacitor based on the sending-end frequency deviation, providing instantaneous inertia support for the system. A power rebalancing mechanism is also designed to effectively address imbalance faults at both the sending and receiving ends, effectively maintaining the stable operation of the transmission system.

[0044] One embodiment of the present invention provides a new energy grid-connected LCC-HVDC transmission system. For details, please refer to [link / reference]. Figure 3 , Figure 3 The diagram shown is a schematic diagram of a new energy grid-connected LCC-HVDC transmission system in one embodiment of the present invention. The system mainly includes: a base-side power generation module, an LCC-HVDC module, and a grid-connected SVG.

[0045] The base-side power generation module includes wind turbine generators, each equipped with a first converter, an inverter group, and a wind turbine connected to a first supercapacitor. Preferably, the first converter is a bidirectional DC / DC converter, which simulates inertia by adjusting the supercapacitor voltage. The wind turbine is preferably a permanent magnet direct-drive wind turbine. Depending on actual needs, the base-side power generation module can also be equipped with photovoltaic generator sets, which include a photovoltaic array, a second converter connected to a second supercapacitor, and a grid-connected inverter. Preferably, the second converter is a bidirectional DC / DC converter.

[0046] Furthermore, the converter group includes machine-side converters and grid-side converters. The machine-side converters integrate rotor field-oriented vector control (MOVDC) to achieve maximum power point tracking during system operation. The grid-side converters integrate grid voltage-oriented vector control (GFDC) to maintain the DC voltage at a set value and control reactive power output during system operation.

[0047] The LCC-HVDC module includes interconnected sending-end and receiving-end converter stations, with one side of the sending-end converter station connected to the base-side AC bus of the base-side power generation module. For example... Figure 3 As shown, the sending-end converter station and the receiving-end converter station are connected by a DC line.

[0048] The grid-type SVG is connected in parallel to the AC bus on the base side to provide grid-connected voltage to the base-side power generation module, establish a stable base-side power grid, and provide commutation voltage to the sending-end converter station.

[0049] The technical features and effects of the new energy grid-type LCC-HVDC transmission system proposed in this embodiment of the invention are the same as those of the new energy grid-type LCC-HVDC transmission method proposed in this embodiment of the invention, and will not be repeated here.

[0050] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for transmitting new energy through a grid-connected LCC-HVDC power grid, applied to the receiving-end power grid, characterized in that, include: The operating status of the receiving-end power grid is monitored in real time, and the frequency deviation and DC voltage deviation of the receiving-end power grid are calculated based on the operating status. The frequency deviation is coupled to the DC voltage deviation to generate a composite signal, which is then input to the receiving-end PI controller for proportional-integral calculation. Using a preset arc-extinguishing angle range as the boundary, the output of the receiving-end PI controller is limited to generate an arc-extinguishing angle control command; In response to the arc extinction angle control command, the receiving-end DC voltage is regulated and sent to the sending-end power grid.

2. The new energy grid-type LCC-HVDC transmission method as described in claim 1, characterized in that, The frequency deviation is coupled to the DC voltage deviation to generate a composite signal. The voltage compensation amount is obtained by multiplying the frequency deviation with a preset droop coefficient. The voltage compensation amount is superimposed on the DC voltage deviation to generate the composite signal.

3. A method for transmitting new energy through a grid-connected LCC-HVDC power grid, applied to the sending-end power grid, characterized in that, include: The adjusted receiving-end DC voltage is received, and the adjusted receiving-end DC voltage is compensated using DC line parameters to obtain a voltage estimate. Based on the voltage estimate, the sending-end frequency reference value is reconstructed, and the sending-end frequency reference value is injected into the grid-type SVG for hierarchical control. The DC link capacitor voltage of the grid-type SVG is monitored synchronously. When the monitoring result meets the preset conditions, the power rebalancing mechanism is triggered. At the same time, the converter is triggered to generate a control signal based on the monitoring result, and the charging and discharging power of the supercapacitor is adjusted by the control signal.

4. The new energy grid-type LCC-HVDC transmission method as described in claim 3, characterized in that, The step of injecting the sending-end frequency reference value into the network-type SVG for hierarchical control includes: The sending-end frequency reference value is injected into the outer control loop of the network-type SVG. Based on the sending-end frequency reference value and the rated voltage amplitude, a voltage reference command is generated and sent to the inner control loop of the network-type SVG. In response to the voltage reference command, voltage and current dual closed-loop control is performed in the inner control loop to generate a target AC voltage on the sending-end AC bus.

5. The new energy grid-type LCC-HVDC transmission method as described in claim 3, characterized in that, The process of obtaining the DC line parameters includes: With the goal of minimizing the error function output, the equivalent resistance and inductance of the DC line are identified online using the least squares method to obtain the parameters of the DC line.

6. The new energy grid-type LCC-HVDC transmission method as described in claim 3, characterized in that, The power rebalancing mechanism is triggered when the monitoring results meet preset conditions, including: When the voltage of the DC link capacitor is detected to exceed a preset first threshold, a DC current limiting operation is triggered. When the DC link capacitor voltage is detected to drop to a preset second threshold, a power transmission recovery operation is performed under a preset voltage slope limit.

7. A new energy grid-connected LCC-HVDC transmission system, applied to the new energy grid-connected LCC-HVDC transmission method described in claims 1-6, characterized in that, include: Base-side power generation modules, LCC-HVDC modules, and grid-type SVG; The base-side power generation module includes wind turbine units, and each wind turbine unit is equipped with a first converter, a converter group and a wind turbine generator connected to a first supercapacitor. The LCC-HVDC module includes a sending-end converter station and a receiving-end converter station that are interconnected; one side of the sending-end converter station is connected to the base-side AC bus of the base-side power generation module. The grid-type SVG is connected in parallel to the AC bus on the base side, and is used to provide grid-connected voltage to the base-side power generation module and commutation voltage to the sending-end converter station.

8. The new energy grid-type LCC-HVDC transmission system as described in claim 7, characterized in that, The base-side power generation module also includes a photovoltaic generator set, which includes a photovoltaic array, a second converter connected to a second supercapacitor, and a grid-connected inverter.

9. The new energy grid-type LCC-HVDC transmission system as described in claim 7, characterized in that, The converter group includes: a machine-side converter and a grid-side converter; The machine-side converter integrates a rotor magnetic field orientation vector algorithm, and the grid-side converter integrates a grid voltage orientation vector algorithm.

10. The new energy grid-type LCC-HVDC transmission system as described in claim 7, characterized in that, The first converter is a bidirectional DC / DC converter.

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