A method for sending and receiving end coordinated primary frequency modulation based on soc prediction and dynamic droop control

Abstract

The application discloses a sending-receiving end cooperative primary frequency modulation method based on SOC prediction and dynamic droop control, relates to the field of power systems and power electronics, and aims at the problems that new energy station of a sending end is difficult to respond to frequency fluctuation of a receiving end power grid in time due to communication delay and frequency modulation response lag in the prior art, and the application comprises the following steps: the receiving end SC-MMC preferentially participates in primary frequency modulation, virtual droop control coefficients and virtual inertia constants that change adaptively with super capacitor SOC are designed based on a logistic function; when the super capacitor releases constant power to support frequency, the super capacitor SOC is predicted according to the communication delay; the frequency modulation droop coefficients of the receiving end and the sending end are dynamically adjusted based on the predicted SOC, the smooth switching of the frequency modulation support main body is realized, and meanwhile, the output change rate of the sending end is constrained to be not more than the climbing rate. The application can effectively eliminate the influence of the communication delay and the frequency modulation response lag, reduce the frequency deviation of the receiving end power grid, and avoid the secondary frequency fluctuation caused when the super capacitor exits the frequency modulation.

Description

Technical Field

[0001] This invention relates to the fields of power systems and power electronics, specifically to a method for coordinated primary frequency regulation between the sending and receiving ends based on SOC prediction and dynamic droop control. Background Technology

[0002] To alleviate the energy crisis and environmental pollution, new energy power generation has developed rapidly. However, with the continuous deepening of the construction of new power systems, a high proportion of new energy power generation is fed into the AC grid through power electronic devices with extremely low inertia levels. As a result, the proportion of synchronous generators in the AC grid is gradually decreasing, leading to a continuous weakening of the grid's inertia and primary frequency regulation capability, which seriously threatens the frequency stability of the receiving-end grid.

[0003] In large-scale renewable energy transmission systems, the sending-end renewable energy power plants are connected to the receiving-end power grid via a high-voltage direct current (HVDC) transmission system. Due to the significant distance between the sending and receiving ends, and considering the modulation and demodulation time during communication, as well as the performance and protocols of the communication equipment, the communication delay between the sending and receiving ends can reach tens of milliseconds. Furthermore, after the frequency information reaches the sending-end power grid, the sending end is still unable to immediately output the power required by the receiving end due to the limited ramp-up rate of the renewable energy units, resulting in a frequency regulation response lag. The long communication delay between the sending and receiving ends, coupled with the significant frequency regulation response lag of the renewable energy itself, prevents the sending end from responding promptly when the receiving end's frequency is disturbed. The delayed power output may cause overshoot, disrupting the system frequency and further jeopardizing the safe and stable operation of the system.

[0004] While integrating supercapacitors into the receiving-end converter can quickly compensate for active power deficits locally, their capacity and cost constraints make it difficult for them to continuously participate in primary frequency regulation. When the supercapacitor's state of charge (SOC) drops to the lower limit, a sudden withdrawal from frequency regulation can cause secondary frequency fluctuations, which is detrimental to the stable operation of the system.

[0005] Therefore, how to achieve coordinated primary frequency regulation between the receiving-end supercapacitor and the sending-end renewable energy power station, while taking into account communication delay and frequency regulation response lag, and ensure dynamic balance of active power in the receiving-end power grid, is an urgent technical problem to be solved. Summary of the Invention

[0006] 1. The technical problem to be solved by the present invention

[0007] The purpose of this invention is to provide a method for coordinated primary frequency regulation between the sending and receiving ends based on SOC prediction and dynamic droop control. This method addresses the problems in existing technologies, such as the difficulty of timely response to frequency fluctuations in the receiving end power grid due to communication delays and lag in frequency regulation response of new energy power plants at the sending end, the difficulty of continuous participation of supercapacitors in primary frequency regulation due to capacity constraints, and the secondary frequency fluctuations caused when supercapacitors withdraw from frequency regulation. The invention achieves coordinated primary frequency regulation between the sending and receiving ends, ensuring the stability of the receiving end power grid frequency.

[0008] 2. Technical Solution To achieve the above objectives, the present invention provides the following technical solution: a primary frequency modulation method for transmitter and receiver coordinated operation based on SOC prediction and dynamic droop control, comprising: S1. Construct an adaptive adjustment function for the virtual droop control coefficient considering the SOC of the supercapacitor; S2. A method for predicting the SOC of supercapacitors that takes into account communication delay is proposed. S3. Design a dynamic adjustment model for the frequency regulation droop coefficient of the sending-end new energy power station; S4. Perform coordinated primary frequency modulation control on the sending and receiving end converters according to the model.

[0009] Preferably, S1 specifically includes: (1) When the SOC of the supercapacitor is in the high range, maintain the frequency modulation droop coefficient at the receiving end. K Maintaining a constant discharge capability of the supercapacitor; (2) Set the SOC warning threshold for supercapacitors or l Compared with the lower limit of supercapacitor SOC or min When the SOC of the supercapacitor drops to or l At the same time, an adaptive adjustment function is constructed based on the logistic function, so that the droop coefficient K decreases smoothly as the SOC of the supercapacitor decreases, gradually reducing the output power of the supercapacitor until it returns to zero, thus avoiding the step disturbance caused by the sudden blocking of the Buck / Boost converter. Design coefficients based on logistic function K :

[0010] In the formula: K 0 and H 0 represents the original VDC and VIC coefficients. The larger the value, the greater the output of the supercapacitor under the same frequency deviation and rate of change. However, an excessively large value will cause the system frequency to oscillate. n represents the sensitivity coefficient; e represents the base of the natural logarithm; n This determines the sensitivity of the coefficient to changes in the supercapacitor's state of charge (SOC); the larger the value, the greater the sensitivity. K and H At the warning value or l The faster the rate of change at a given location.

[0011] Preferably, S2 specifically includes: The SC-MMC modular multilevel converter with an embedded supercapacitor at the receiving end employs frequency-power droop control, and the power output and frequency deviation satisfy the following relationship:

[0012] In the formula: K Δ is the sag coefficient at the receiving end. f This is for frequency deviation; When the receiving end frequency is disturbed, the SC-MMC can independently perform primary frequency regulation; after the receiving end grid frequency reaches steady state under the primary frequency regulation of the SC-MMC, the supercapacitor inside the SC-MMC releases constant power to maintain frequency stability; the SOC decreases at a constant rate. When the SOC drops close to the warning value, the output power of the SC-MMC will decrease slowly. At this time, the sending end needs to gradually increase the active power output at the same rate of change in order to maintain the dynamic balance of the receiving end power. Supercapacitors release approximately constant power P SC When frequency support is applied, its remaining energy is calculated by subtracting its released energy from its initial energy:

[0013] In the formula: E 1 and U 1 represents the remaining energy and voltage of the supercapacitor after it has released energy; N SC The number of supercapacitors participating in the discharge; C SC The capacitance value of the supercapacitor is represented by t; time is represented by t. P SC This indicates the power released by the supercapacitor. Due to communication delay t The integral term in the formula is relatively small, and is approximately a product; therefore, after the communication delay, the corresponding supercapacitor voltage when the transmitting end outputs power is relatively small. U pre and the corresponding SOC or pre Due to communication delay t Supercapacitor voltage before communication delay U Joint forecast:

[0014]

[0015] In the formula, t represents the communication delay time; U represents the supercapacitor voltage before the communication delay.

[0016] Preferably, the construction of the S3 dynamic adjustment model specifically includes: Substituting the predicted SOC into the frequency modulation droop coefficient calculation formula in S1, the VDC coefficient considering communication delay can be calculated during the frequency recovery phase. K pre Prediction is performed; the formula for calculating the frequency modulation droop coefficient is:

[0017] In the formula: K send0 This represents the original sag coefficient at the feed end; K pre VDC coefficient represents communication delay; K 0 represents the original VDC coefficient; to completely eliminate the effect of frequency modulation response lag, the rate of power increase at the sending end is controlled to be less than the ramp rate of the sending end station.

[0018] Preferably, the droop coefficients established in S1-S3 are applied to the frequency adjustment process to achieve frequency support for the receiving end system; S4 specifically includes: The sending-end converter station adopts a frequency-power droop control strategy, which theoretically increases the power generation. P send The relationship with frequency is as follows;

[0019] In the formula: K send Δ is the feed end sag coefficient. f The frequency deviation is a factor; the additional power required at the transmitting end is affected by the supercapacitor's state of charge (SOC). When the supercapacitor's state of charge (SOC) is high, the dynamic droop coefficient at the sending end... K send =0, meaning the frequency modulation is handled independently by the receiving-end SC-MMC alone; As the SOC of supercapacitors continues to decrease, dynamic adjustment K send Simultaneously increase the active power generation at the sending end, so that the power increase at the sending end can offset the power attenuation of the supercapacitor at the receiving end, smoothly complete the switching of the frequency regulation support main body, and maintain the dynamic balance of active power in the receiving end power grid.

[0020] Preferably, the SC-MMC adopts a supercapacitor embedded modular multilevel topology and is applied to the receiving end of a dual-end high-voltage direct current transmission system.

[0021] As a preferred approach, from S1 to S4, each step is the basis for the execution of the next step. These four steps are interconnected and executed sequentially, forming an organic and inseparable whole.

[0022] Compared with the prior art, the transmitting and receiving end coordinated primary frequency modulation method based on SOC prediction and dynamic droop control provided by the present invention has the following beneficial effects: 1. By using SC-MMC at the receiving end for fast inertia support and primary frequency modulation during the communication delay at the sending and receiving ends and the frequency modulation response lag at the sending end, frequency drop during the delay period is effectively avoided.

[0023] 2. By using a supercapacitor SOC prediction method that takes into account communication delay, the impact of communication delay is effectively eliminated.

[0024] 3. By taking into account the dynamic droop factor of SOC, a smooth transfer of frequency modulation power support from SC-MMC to the sending-end station is achieved. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A flowchart illustrating the transmitting and receiving end coordinated primary frequency modulation method based on SOC prediction and dynamic droop control provided in an embodiment of the present invention; Figure 2 A schematic diagram of the topology of the supercapacitor-embedded modular multilevel converter (SC-MMC) provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of a dual-end high-voltage direct current transmission system based on receiving-end SC-MMC provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the frequency modulation coefficient variation curve at the transmitting and receiving ends, considering the SOC of the supercapacitor, provided for an embodiment of the present invention. Detailed Implementation

[0027] 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. 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.

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0029] Example Please refer to Figure 1 to Figure 4 As shown: To address the problems mentioned in the technical solutions, this application provides a method for coordinated primary frequency modulation at both the transmitting and receiving ends based on SOC prediction and dynamic droop control. The technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them, and do not constitute a limitation on this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the protection scope of this invention.

[0030] The method includes: Step 1: Construct an adaptive adjustment function for the virtual droop control coefficient considering the supercapacitor's state of charge (SOC): A schematic diagram of the topology of the SC-MMC (supercapacitor-embedded modular multilevel converter) used in this invention is shown in [the diagram]. Figure 2 Provided.

[0031] (1) When the SOC of a supercapacitor is at a high level, in order to maintain its discharge capability, the receiving end frequency modulation droop coefficient is... K It should remain basically unchanged.

[0032] (2) To avoid step disturbances caused by sudden blocking of the Buck / Boost converter when the SOC drops to the lower limit, and considering the ramp rate limitation of the sending-end station, a setting should be implemented. K The output power of the supercapacitor decreases slowly as the State of Charge (SOC) decreases, gradually reducing the output until it reaches zero, and a new steady-state equilibrium is gradually established. Therefore, as the SOC decreases to near zero... or min During the process, set an early warning value. or l Once the SOC drops to near this level, immediately and actively reduce it. K .

[0033] Design coefficients based on logistic function K :

[0034] In the formula: K 0 and H 0 represents the original VDC and VIC coefficients. The larger the value, the greater the output of the supercapacitor under the same frequency deviation and rate of change. However, an excessively large value will cause the system frequency to oscillate. n This determines the sensitivity of the coefficient to changes in SOC; the larger the value, the greater the sensitivity. K andH At the warning value or l The faster the rate of change at a given location.

[0035] Step 2: Propose a supercapacitor SOC prediction method that takes into account communication delay; Specifically, the receiving-end SC-MMC also adopts a frequency-power droop control strategy, and its power-frequency relationship is as follows:

[0036] In the formula: K Δ is the sag coefficient at the receiving end. f This represents the frequency deviation.

[0037] When the receiving-end frequency is disturbed, the SC-MMC can independently perform primary frequency regulation. After the receiving-end grid frequency reaches steady state under the primary frequency regulation of the SC-MMC, the supercapacitor releases constant power to maintain frequency stability. At this time, the State of Charge (SOC) decreases at a constant rate. When it approaches the warning value, the output power of the SC-MMC will slowly decrease. At this time, the sending end needs to gradually increase its active power output at the same rate of change to maintain the dynamic balance of power at the receiving end.

[0038] However, the transmission of the SOC status signal from the receiving-end SC-MMC to the sending-end control loop still involves a communication delay. To address this issue, this invention proposes an SOC prediction method that takes into account communication delay.

[0039] Supercapacitors release approximately constant power P SC When frequency support is applied, its remaining energy can be calculated by subtracting its released energy from its initial energy:

[0040] In the formula: E 1 and U 1 represents the remaining energy and voltage of the supercapacitor after it has released energy; N SC This refers to the number of supercapacitors participating in the discharge.

[0041] Considering communication delay t The value is relatively small, and the integral term in the formula can be approximated as a product. Therefore, after the communication delay, the corresponding supercapacitor voltage when the transmitting end outputs power is relatively small. U pre and the corresponding SOC or pre It can be caused by communication delay t Supercapacitor voltage before communication delay U Joint forecast:

[0042]

[0043] Step 3: Design a dynamic adjustment model for the frequency regulation droop coefficient of the sending-end renewable energy power station: Specifically, the predicted SOC (i.e. or pre Substituting the formula for calculating the frequency modulation droop factor in step 1, the VDC factor considering communication delay can be calculated during the frequency recovery phase. K pre Make predictions.

[0044] To address the asynchrony in communication control between the sending and receiving ends caused by communication delays, the droop coefficient at the sending end is adjusted. K send Designed as follows:

[0045] In the formula: K send0 This represents the original sag coefficient at the sending end.

[0046] To completely eliminate the effects of frequency modulation response lag, the rate of power increase at the sending end must be controlled to be less than the ramp rate of the sending end station.

[0047] Step 4: Propose a coordinated primary frequency modulation control method for the transmitting and receiving ends: Specifically, the sending-end converter station adopts a frequency-power droop control strategy, which theoretically increases the generated power. P send The relationship with frequency is as follows.

[0048]

[0049] In the formula: K send Δ is the feed end sag coefficient. f This represents the frequency deviation.

[0050] The additional power required at the transmitting end is affected by the supercapacitor's state of charge (SOC). When the supercapacitor's SOC is at a high level, K send = 0. That is, during the short period of time when the receiving end frequency is disturbed, the sending end does not transmit power, and only the receiving end SC-MMC participates in the first frequency modulation; after the receiving end frequency recovers to a steady state with the support of the SC-MMC, as the SOC of the supercapacitor decreases, the dynamic droop coefficient of the sending end is used to eliminate the power disturbance caused by the decrease of the supercapacitor SOC and the communication delay, so that the increased power transmitted by the sending end cancels out the decrease in the output of the SC-MMC, and maintains the dynamic stability of the receiving end power.

[0051] Because the sending-end renewable energy power plants connected via the high-voltage direct current (HVDC) transmission system are far from the receiving-end power grid, the communication delay between the sending and receiving ends can reach tens of milliseconds, considering the modulation and demodulation time during communication, as well as the performance and protocol of the communication equipment. Furthermore, after the frequency information reaches the sending-end power grid, the sending end is still unable to immediately output the power required by the receiving end due to the limited ramp-up rate of the renewable energy units, resulting in a frequency regulation response lag. The long communication delay between the sending and receiving ends, coupled with the significant frequency regulation response lag of the renewable energy units themselves, prevents the sending end from responding promptly when the receiving end's frequency is disturbed. The delayed power output may cause overshoot, disturbing the system frequency and further jeopardizing the safe and stable operation of the system.

[0052] Existing technologies convert frequency variations in the receiving-end power grid into DC voltage variations in the HVDC transmission system, allowing the sending-end power grid to sense these frequency changes without a communication system. However, significant frequency disturbances can cause DC voltage to exceed limits. Furthermore, the direct mapping between frequency and DC voltage requires increasing DC power while decreasing DC voltage, leading to a substantial increase in DC current, which is detrimental to the safe operation of the converter. Conversely, the inverse mapping between frequency and DC voltage depends on the number of redundant submodules in the MMC (Multi-Module Control). When the number of redundant modules is small, the advantages of the inverse mapping cannot be fully utilized; while when the number of redundant modules is large, they cannot be fully utilized under other operating conditions, resulting in waste.

[0053] This embodiment can be used to solve the above problems. Specifically, it is manifested in: 1. By using SC-MMC at the receiving end for fast inertia support and primary frequency modulation during the communication delay at the sending and receiving ends and the frequency modulation response lag at the sending end, frequency drop during the delay period is effectively avoided.

[0054] 2. By using a supercapacitor SOC prediction method that takes into account communication delay, the impact of communication delay is effectively eliminated.

[0055] 3. By taking into account the dynamic droop factor of SOC, a smooth transfer of frequency modulation power support from SC-MMC to the sending-end station is achieved.

[0056] It is worth noting that the contents not described in detail in the embodiments of the present invention belong to the prior art known to those skilled in the art.

[0057] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. The information disclosed in the background section is intended only to enhance the understanding of the overall background technology of the present invention and should not be construed as an admission or implication in any way that such information constitutes prior art known to those skilled in the art.

[0058] It should be noted that the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0059] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for coordinated primary frequency modulation at the transmitting and receiving ends based on SOC prediction and dynamic droop control, characterized in that, include: S1. Construct an adaptive adjustment function for the virtual droop control coefficient considering the SOC of the supercapacitor; S2. A method for predicting the SOC of supercapacitors that takes into account communication delay is proposed. S3. Design a dynamic adjustment model for the frequency regulation droop coefficient of the sending-end new energy power station; S4. Perform coordinated primary frequency modulation control on the sending and receiving end converters according to the model.

2. The method for coordinated primary frequency modulation of the transmitting and receiving ends based on SOC prediction and dynamic droop control according to claim 1, characterized in that, S1 specifically includes: (1) When the SOC of the supercapacitor is in the high range, maintain the frequency modulation droop coefficient at the receiving end. K Maintaining a constant discharge capability of the supercapacitor; (2) Set the SOC warning threshold for supercapacitors η l Compared with the lower limit of supercapacitor SOC η min When the SOC of the supercapacitor drops to η l At the same time, an adaptive adjustment function is constructed based on the logistic function, so that the droop coefficient K decreases smoothly as the SOC of the supercapacitor decreases, gradually reducing the output power of the supercapacitor until it returns to zero, thus avoiding the step disturbance caused by the sudden blocking of the Buck / Boost converter. Design coefficients based on logistic function K : In the formula: K 0 and H 0 represents the original VDC and VIC coefficients. The larger the value, the greater the output of the supercapacitor under the same frequency deviation and rate of change. However, an excessively large value will cause the system frequency to oscillate. n represents the sensitivity coefficient; e represents the base of the natural logarithm; n This determines the sensitivity of the coefficient to changes in the supercapacitor's state of charge (SOC); the larger the value, the greater the sensitivity. K and H At the warning value η l The faster the rate of change at a given location.

3. The method for coordinated primary frequency modulation of the transmitting and receiving ends based on SOC prediction and dynamic droop control according to claim 1, characterized in that, S2 specifically includes: The SC-MMC modular multilevel converter with an embedded supercapacitor at the receiving end employs frequency-power droop control, and the power output and frequency deviation satisfy the following relationship: In the formula: K Δ is the sag coefficient at the receiving end. f This is for frequency deviation; When the receiving end frequency is disturbed, the SC-MMC can independently perform primary frequency regulation; after the receiving end grid frequency reaches steady state under the primary frequency regulation of the SC-MMC, the supercapacitor inside the SC-MMC releases constant power to maintain frequency stability; the SOC of the supercapacitor decreases at a constant rate. When the SOC of the supercapacitor drops close to the warning value, the output power of the SC-MMC will decrease slowly. At this time, the sending end needs to gradually increase the active power output at the same rate of change in order to maintain the dynamic balance of the power at the receiving end. Supercapacitors release approximately constant power P SC When frequency support is applied, its remaining energy is calculated by subtracting its released energy from its initial energy: In the formula: E 1 and U 1 represents the remaining energy and voltage of the supercapacitor after it has released energy; N SC The number of supercapacitors participating in the discharge; C SC d represents the capacitance value of the supercapacitor; d represents the differential operator; t represents time. P SC This indicates the power released by the supercapacitor; Due to communication delay t The integral term in the formula is relatively small, and is approximately a product; therefore, after the communication delay, the corresponding supercapacitor voltage when the transmitting end outputs power is relatively small. U pre and the corresponding SOC η pre Due to communication delay t Supercapacitor voltage before communication delay U Joint forecast: In the formula, t represents the communication delay time; U represents the supercapacitor voltage before the communication delay.

4. The method for coordinated primary frequency modulation of the transmitting and receiving ends based on SOC prediction and dynamic droop control according to claim 1, characterized in that, The construction of the S3 dynamic adjustment model specifically includes: Substituting the predicted supercapacitor SOC into the frequency modulation droop coefficient calculation formula in S1, the VDC coefficient considering communication delay can be calculated during the frequency recovery phase. K pre Prediction is performed; the formula for calculating the frequency modulation droop coefficient is: In the formula: K send0 The original sag coefficient at the feed end; K pre VDC coefficient represents communication delay; K 0 represents the original VDC coefficient; to completely eliminate the effect of frequency modulation response lag, the rate of power increase at the sending end is controlled to be less than the ramp rate of the sending end station.

5. The method for coordinated primary frequency modulation at the transmitting and receiving ends based on SOC prediction and dynamic droop control according to claim 1, characterized in that, The droop coefficients established in S1-S3 are applied to the frequency adjustment process to achieve frequency support for the receiving end system; S4 specifically includes: The sending-end converter station adopts a frequency-power droop control strategy, which theoretically increases the generated power. P send The relationship with frequency is as follows; In the formula: K send Δ is the feed end sag coefficient. f The frequency deviation is a factor; the additional power required at the transmitting end is affected by the supercapacitor's state of charge (SOC). When the supercapacitor's SOC is high, the dynamic droop coefficient Ksend at the sending end is 0, and the frequency modulation is handled independently by the receiving end SC-MMC. As the SOC of the supercapacitor continues to decline, the dynamic adjustment of Ksend synchronously increases the active power generated at the sending end, so that the power increment at the sending end offsets the power decay of the supercapacitor at the receiving end, smoothly completing the switching of the frequency regulation support main body and maintaining the dynamic balance of active power in the receiving end power grid.

6. The method for coordinated primary frequency modulation of the transmitting and receiving ends based on SOC prediction and dynamic droop control according to claim 1, characterized in that, The SC-MMC adopts a supercapacitor embedded modular multilevel topology and is applied to the receiving end of a dual-end high-voltage direct current transmission system.

7. The method for coordinated primary frequency modulation of the transmitting and receiving ends based on SOC prediction and dynamic droop control according to claim 1, characterized in that, From S1 to S4, each step is the basis for the execution of the next step. S1-S4 are interconnected and executed sequentially, forming an organic and inseparable whole.

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