A control method, device, equipment and medium for a multi-terminal cascaded DC system

Abstract

The present application relates to power transmission system technical field, disclose a kind of control method, device, equipment and medium for multi-terminal cascaded DC system, the method includes obtaining the real-time operation data of cascaded converter station in multi-terminal cascaded DC system, to determine the droop coefficient of each cascaded converter station under different operating conditions, and then quantize its voltage reference value;The port voltage of each cascaded converter station is calculated, and the voltage reference value of cascaded converter station is corrected and current imbalance compensated according to the deviation amount of port voltage and voltage reference value, to obtain voltage adjustment value below to corresponding cascaded converter station, and then control it according to its cascaded control mode, trigger angle instruction is generated by PI algorithm and is executed, to realize the control of multi-terminal cascaded DC system;Effectively solve the DC voltage imbalance problem in multi-terminal cascaded DC system, and then ensure the stable operation and excellent control characteristics of system, realize safe and reliable power transmission of DC system.

Description

Technical Field

[0001] This invention relates to the field of power transmission system technology, and in particular to a control method, apparatus, equipment and medium for multi-terminal cascaded DC systems. Background Technology

[0002] Ultra-high voltage (UHV) multi-terminal cascaded DC transmission systems have advantages in long-distance, high-capacity power transmission, enabling multiple power sources and multiple receiving points, and have promising development prospects. Currently, most of the multi-terminal DC transmission systems that have been built are in parallel topologies, and no cascaded multi-terminal projects have been put into operation. Meanwhile, existing control strategies for DC transmission systems are mostly geared towards multi-terminal VSCs, multi-terminal LCC-VSCs, or all-LCC parallel connections, with very little research on cascading. Furthermore, they typically refer to conventional two-terminal control strategies, selecting a combination of constant current or constant DC voltage at the sending end. However, how to adjust this control strategy when there is DC voltage imbalance has not yet been studied.

[0003] Therefore, how to provide a control strategy for DC voltage imbalance in multi-terminal cascaded DC systems to ensure stable system operation and excellent control characteristics, and to realize safe and reliable power transmission of DC systems, has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] This invention provides a control method, apparatus, equipment, and medium for multi-terminal cascaded DC systems, addressing the problem of how to provide a control strategy for DC voltage imbalance in multi-terminal cascaded DC systems to ensure stable system operation and excellent control characteristics, thereby achieving safe and reliable power transmission in DC systems.

[0005] To address the aforementioned technical problems, the first aspect of this invention provides a control method for a multi-terminal cascaded DC system, comprising:

[0006] To acquire real-time operating data and operating conditions of all cascaded converter stations in a multi-terminal cascaded DC system;

[0007] Based on the real-time operating conditions, the static droop coefficient and dynamic droop coefficient of each cascaded converter station are determined, and combined with the real-time operating data, the voltage reference value of each cascaded converter station is quantified.

[0008] The actual port voltage of each cascaded converter station is quantified, and the cascaded converter station with deviation is taken as the target converter station. The voltage reference value of the target converter station is then adaptively corrected and the current imbalance is compensated based on the deviation to obtain the voltage adjustment value.

[0009] The voltage adjustment value of the target converter station and the voltage reference values ​​of the other cascaded converter stations are respectively sent to each of the cascaded converter stations to control each of the cascaded converter stations to generate and execute firing angle commands through a PI algorithm according to its own cascaded control mode, so as to realize the control of the multi-terminal cascaded DC system.

[0010] A second aspect of the present invention provides a control device for a multi-terminal cascaded DC system, comprising:

[0011] The data acquisition module is used to acquire real-time operating data and real-time operating conditions of all cascaded converter stations in a multi-terminal cascaded DC system.

[0012] The voltage quantization module is used to determine the static droop coefficient and dynamic droop coefficient of each cascaded converter station based on the real-time operating conditions, so as to combine with the real-time operating data to quantify the voltage reference value of each cascaded converter station.

[0013] The voltage adjustment module is used to quantify the actual port voltage of each cascaded converter station, so as to take the cascaded converter station with deviation as the target converter station, and perform voltage adaptive correction and current imbalance compensation on the voltage reference value of the target converter station according to the deviation to obtain the voltage adjustment value.

[0014] The instruction execution module is used to send the voltage adjustment value of the target converter station and the voltage reference value of the other cascaded converter stations to each of the cascaded converter stations, so as to control each of the cascaded converter stations to generate and execute the trigger angle instruction through the PI algorithm according to its own cascaded control mode, so as to realize the control of the multi-terminal cascaded DC system.

[0015] A third aspect of the present invention provides an electronic device including a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein the processor, when executing the computer program, implements the control method for a multi-terminal cascaded DC system as described above.

[0016] A fourth aspect of the present invention provides a computer-readable storage medium comprising a stored computer program, wherein when the device containing the computer-readable storage medium executes the computer program, it implements the control method for a multi-terminal cascaded DC system as described above.

[0017] Compared with the prior art, the beneficial effects of the embodiments of the present invention are as follows:

[0018] By acquiring real-time operating data and conditions of all cascaded converter stations to dynamically determine static and dynamic droop coefficients, the voltage reference values ​​of each converter station can be quantified more accurately, effectively responding to various operating condition changes, enhancing system stability in complex environments, and reducing the risk of system instability caused by fixed parameters. Through adaptive voltage correction and current imbalance compensation for converter stations with deviations, the output voltage of each converter station is ensured to meet system requirements, improving the voltage control accuracy of the entire multi-terminal cascaded DC system and guaranteeing power quality. Adopting a control method based on precise parameters and adaptive adjustment optimizes control performance, enabling efficient and stable control under various operating conditions, reducing energy loss, improving system operating efficiency, and ensuring that the system can accurately and flexibly adjust the control strategies of converter stations under different operating modes. This gives the multi-terminal cascaded DC transmission system reliable operation and excellent response characteristics, achieving safe and reliable power transmission from the DC system. Attached Figure Description

[0019] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the 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.

[0020] Figure 1 This is a flowchart of a control method for a multi-terminal cascaded DC system provided in a certain embodiment of the present invention;

[0021] Figure 2 This is a power step result diagram provided in a certain embodiment of the present invention;

[0022] Figure 3 This is a current step result diagram provided in a certain embodiment of the present invention;

[0023] Figure 4 This is a diagram showing the result of a DC line fault according to a certain embodiment of the present invention;

[0024] Figure 5 This is a diagram showing the results of an AC line fault according to a certain embodiment of the present invention;

[0025] Figure 6 This is a diagram showing the change in current and voltage loops after a valve short circuit in a converter station, provided in a certain embodiment of the present invention.

[0026] Figure 7 This is a structural diagram of a control device for a multi-terminal cascaded DC system provided in a certain embodiment of the present invention;

[0027] Figure 8 This is a structural diagram of an electronic device provided in a certain embodiment of the present invention;

[0028] Figure label:

[0029] Among them, 10 is the data acquisition module; 20 is the voltage quantization module; 30 is the voltage adjustment module; 40 is the instruction execution module; 5000 is the electronic device; 5001 is the processor; 5002 is the bus; 5003 is the memory; and 5004 is the transceiver. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings and examples. 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.

[0031] 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.

[0032] 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 system 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 according to the specific circumstances.

[0033] 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 merely for describing specific embodiments 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.

[0034] In one embodiment, such as Figure 1 As shown, the first aspect of the present invention provides a control method for a multi-terminal cascaded DC system, comprising:

[0035] S1. Obtain real-time operating data and real-time operating conditions of all cascaded converter stations in the multi-terminal cascaded DC system; the real-time operating data includes DC current;

[0036] Specifically, this invention installs voltage sensors, current sensors, and power measurement devices on each cascaded converter station (also referred to as a converter station or DC converter station) within a multi-terminal cascaded DC system to collect real-time DC voltage, DC current, and power data from each converter station, and uses this data along with the collected rated voltage, rated current, rated resistance, and line length of each converter station as real-time operating data. Simultaneously, the system monitors the operating conditions of each converter station. When multiple converter stations at the sending end are all in operation, the system is determined to be in full valve group operation mode; otherwise, the real-time operating condition of the multi-terminal cascaded DC system is in non-full valve group operation mode, and the number of cascaded converter stations in operation is determined.

[0037] S2. Based on the real-time operating conditions, determine the static droop coefficient and dynamic droop coefficient of each cascaded converter station, and combine them with the real-time operating data to quantify the voltage reference value of each cascaded converter station.

[0038] In one embodiment, step S2 includes:

[0039] The operating converter stations in the multi-terminal cascaded DC system are determined based on the real-time operating conditions, and the static droop coefficient is determined based on the rated equivalent resistance of the operating converter stations.

[0040] Real-time environmental data of each of the operating converter stations is obtained, and an environmental resistance model is constructed based on the real-time environmental data to quantify the real-time resistance value of each of the operating converter stations.

[0041] The dynamic droop coefficient of each operating converter station is determined based on its real-time resistance value.

[0042] The rated DC voltage reference value and rated current of each of the cascaded converter stations are obtained, and combined with each of the DC currents, static droop coefficients and dynamic droop coefficients, to quantify the voltage reference value of each of the cascaded converter stations.

[0043] Specifically, when multiple converter stations are operating at the sending end, and the actual transmission power is not rated, changes in DC power and impedance will cause variations in the reference voltage of each converter station, but the DC output voltage remains constant. Based on this, this invention uses actually measured current and voltage parameters, designs adaptive voltage distribution coefficients based on different operating conditions and droop characteristics, continuously calculates the voltage reference value of the converter stations, and constructs droop curves based on the rated voltage and time-varying line impedance of each converter station.

[0044] The operating converter stations are determined based on the real-time operating conditions of the system. This means that the converter stations currently in normal operation are considered the operating converter stations. The static droop coefficient of the corresponding converter station is calculated based on the inter-line resistance of the operating converter station. This coefficient represents the single-station resistance equalization value, and its calculation process is expressed by the following formula:

[0045] ki=(RN1+RN2+···+RN(n-1)) / n

[0046] In the formula, ki is the static droop coefficient of the i-th cascaded converter station, i = n-1; RN(n-1) is the rated equivalent resistance between the (n-1)-th and n-th cascaded converter stations; n is the number of cascaded converter stations in the multi-terminal cascaded DC system.

[0047] DC transmission conductors mostly use six-split steel-cored aluminum stranded wire. Their DC resistance is related to the conductor's type and specifications. The DC resistance value R0 at 20℃ can be determined first based on the conductor type. Then, using the formula Rd = R0 * L (where Rd is the line resistance, R0 is the DC resistance per kilometer, and L is the line length), the DC resistance parameter needs to be dynamically calculated when the temperature changes. Real-time temperature data from each operating converter station is obtained as real-time environmental data, and an environmental resistance model is constructed based on the temperature of each operating converter station. This model describes the relationship between environmental factors and resistance, expressed by the following formula:

[0048] Rt=R0×(1+β×(t-t0))

[0049] In the formula, Rt is the real-time resistance value; R0 is the reference resistance; t is the real-time temperature data; t0 is the reference temperature data (usually 20℃); β is the temperature coefficient of resistance of the conductor material (1 / ℃); among which, the β values ​​of common materials are: copper: β=0.00393 (at 20℃); aluminum: β=0.00403 (at 20℃); steel-cored aluminum stranded wire (aluminum is the dominant material): β=0.004 (approximate value).

[0050] Next, based on the environmental resistance model of each operating converter station, the real-time resistance value of each operating converter station can be determined. Based on the difference between the real-time resistance value and its own rated equivalent resistance, the dynamic droop coefficient of each operating converter station can be determined. This coefficient is dynamically configured according to the real-time impedance value and is expressed by the following formula:

[0051] kj=(△R1+△R2+···+△R(n-1)) / n

[0052] In the formula, kj is the dynamic droop coefficient, where j = n-1; △R(n-1) is the change in resistance of the connecting line between the (n-1)th cascade converter station and the nth cascade converter station, which is the difference between the real-time resistance value of the corresponding cascade converter station and its line resistance.

[0053] Finally, the rated DC voltage reference values ​​and rated currents of each cascaded converter station are obtained. These are then combined with the corresponding DC current, static droop coefficient, and dynamic droop coefficient to quantify the voltage reference value of the cascaded converter station. The calculation process is expressed by the following formula:

[0054] Udiref=UdirefN-ki×(Idc-IdN)-kj×Idc

[0055] In the formula, Udiref is the voltage reference value; UdirefN is the rated DC voltage reference value; Idc is the actual current at the outlet of a single converter station, which can also be understood as DC current; and IdN is the rated current.

[0056] For non-full-valve group operation modes, which differ from traditional DC transmission projects, the connection lines between operating and non-operating converter stations still need to be considered. Under this operating condition, the reference value of the rated voltage at the port will change. For example, when the full valve group is operating, the DC outlet voltage is 800kV, but when only a single valve group is operating, the DC outlet voltage will drop to 400kV. For traditional two-terminal DC transmissions without intermediate transmission lines, the DC voltage reference value will not change when the operating mode changes. However, for multi-terminal cascaded topologies, the reference value of the converter station will also change with the operating mode when the operating mode changes. The calculation process is the same, only the value of n used in the actual calculation is different.

[0057] This invention determines the operating converter station based on real-time operating conditions and determines the static droop coefficient based on its rated equivalent resistance. This ensures that the static droop coefficient closely matches the current actual operating state of the system, avoiding the problem of being unable to adapt to different operating conditions due to the use of fixed coefficients, thus improving the accuracy and adaptability of control. Real-time environmental data is acquired and an environmental resistance model is constructed to quantify the real-time resistance value of the operating converter station, thereby determining the dynamic droop coefficient. By considering the influence of environmental factors on the converter station resistance, the dynamic droop coefficient can more accurately reflect the characteristics of the system during dynamic changes, enhancing the system's ability to respond to environmental changes. When quantifying the voltage reference value of the cascaded converter station, the static and dynamic characteristics of the system and various influencing factors are comprehensively considered, resulting in a more accurate and reasonable voltage reference value. This provides a reliable basis for subsequent system control and helps improve the stability and power quality of the entire multi-terminal cascaded DC system.

[0058] S3. Quantify the actual port voltage of each cascaded converter station, take the cascaded converter station with deviation as the target converter station, and perform voltage adaptive correction and current imbalance compensation on the voltage reference value of the target converter station according to the deviation to obtain the voltage adjustment value.

[0059] In one embodiment, quantifying the actual port voltage of each of the cascaded converter stations includes:

[0060] The inter-station line lengths of each of the cascaded converter stations are obtained to quantify the line resistance of each of the cascaded converter stations.

[0061] The line resistance of the multi-terminal cascaded DC system is determined based on the line resistance of each of the aforementioned lines, and combined with the DC current of each of the aforementioned cascaded converter stations to determine the actual port voltage of each of the aforementioned cascaded converter stations.

[0062] Specifically, this invention quantifies the line resistance based on the inter-station line length of cascaded converter stations. The line resistances between each converter station are added together to obtain the line resistance of the multi-terminal cascaded DC system. The actual port voltage is determined by combining the system's line resistance with the DC current of each cascaded converter station. It is important to note that the actual port voltage of each cascaded converter station is the voltage obtained after connecting all the converter stations preceding it in series. For example, the actual port voltage of the third cascaded converter station is the sum of the voltages of the first and second cascaded converter stations plus the voltage of the third cascaded converter station itself. Therefore, the actual port voltage of each cascaded converter station is calculated using the following formula:

[0063] Udn=Ud1+Ud2+···+Ud(n-1)+Idc*(Rd1+Rd2+···+Rd(n-1))

[0064] In the formula, Udn is the actual port voltage of the nth converter station; Ud1, Ud2, and Ud(n-1) are the port voltages of converter stations 1, 2, and n, respectively; and Rd(n-1) is the line resistance between the (n-1)th converter station and the nth converter station.

[0065] This invention quantifies line resistance by obtaining the length of the inter-station line, which can more accurately reflect the resistance characteristics of the actual line and improve the accuracy of system control. Precise quantification of the actual port voltage helps to more accurately grasp the working status of each converter station in a multi-terminal cascaded DC system, thereby enhancing the stability and reliability of the entire system. This method does not depend on a specific system topology and can quantify the actual port voltage of multi-terminal cascaded DC systems of different sizes and layouts, and has strong versatility and adaptability.

[0066] Next, the deviation of each operating converter station is quantified using the following formula:

[0067] ΔUd=(Ud-UdN) / UdN×100%

[0068] In the formula, ΔUd is the deviation; UdN is the rated DC voltage of the DC line port of the nth cascaded converter station after all stations at the sending end are cascaded.

[0069] Converter stations with deviations greater than a preset value (preferably 3%) are designated as target converter stations. For converter stations without deviations, their reference voltage values ​​are used as voltage adjustment values.

[0070] In one embodiment, the step of performing voltage adaptive correction and current imbalance compensation on the voltage reference value of the target converter station based on the deviation to obtain a voltage adjustment value includes:

[0071] When it is determined that the deviation meets the first deviation condition, the first correction gain is determined based on the deviation, and the voltage distribution coefficient of the target converter station is determined in combination with the voltage reference value of the target converter station to perform voltage adaptive correction and obtain the voltage correction value.

[0072] When the deviation is determined to meet the second deviation condition, the second correction gain is determined based on the deviation, and the voltage distribution coefficient of the target converter station is determined in combination with the voltage reference value of the target converter station to perform voltage adaptive correction and obtain the voltage correction value.

[0073] Specifically, this invention designs an initial voltage distribution coefficient αi for each operating converter station. Under no-load conditions, the DC current Id = 0, satisfying Σαi = 1, and αi = Udiref0 / UdN, where Udiref0 represents the DC voltage reference value of the i-th converter station under no-load conditions. This ensures that the voltage of each converter station is evenly distributed according to the rated ratio, and the total voltage equals the system design value. As the DC power increases, the DC resistance voltage drop increases, and the voltage distributed to each converter station gradually decreases, Σαi ≤ 1. Under rated conditions, αiN = UdiNref / UdN for each converter station; during actual operation, the distribution coefficient is normally distributed according to the rated coefficient.

[0074] When the DC power remains constant, changes in the DC port voltage will also cause changes in the reference values ​​of each converter station. However, these changes in voltage reference values ​​are not due to the converter station's own control, but may be caused by measurement and receiving-end control. In such cases, the Udiref of the converter station should be corrected accordingly based on the deviation coefficient.

[0075] When the deviation of the operating converter station does not meet the deviation condition, that is, |ΔUdi|≤3%, the current allocation coefficient αi is maintained and multiplied by the original voltage reference value to obtain the voltage correction value.

[0076] When the deviation of a target converter station meets the first deviation condition, i.e., 3% < |ΔUdi| ≤ 5%, the DC voltage control of the converter station should start calculating the correction reserve. The first correction gain is determined based on the deviation to ensure that the adjustment amount matches the degree of deviation. The first correction gain is kcorr1 = 1 / |ΔUdi|. Combined with the voltage reference value of the target converter station, the voltage distribution coefficient of the target converter station is determined for voltage adaptive correction to obtain the voltage correction value. At this time, the voltage distribution coefficient Δαi is linearly related to the voltage deviation: Δαi = kcorr1 × Udiref. Finally, the voltage correction value can be obtained by multiplying Δαi by the original voltage reference value.

[0077] When the deviation of a target converter station meets the second deviation condition, i.e., ΔUdi>5%, the reduction magnitude of Δαi should be further increased to further reduce the rectifier voltage. The second correction gain is determined based on the deviation to ensure that the adjustment amount matches the degree of deviation. The second correction gain is kcorr2=1 / |ΔUdi|^2. Combined with the voltage reference value of the target converter station, the voltage allocation coefficient of the target converter station is determined for voltage adaptive correction to obtain the voltage correction value. At this time, the voltage allocation coefficient Δαi is linearly related to the voltage deviation: Δαi=kcorr2×Udiref. Finally, by multiplying Δαi by the original voltage reference value, the voltage correction value can be obtained.

[0078] In addition, the voltage correction adjustment range of each converter station is limited to within 2% of the initial coefficient, and the correction effect is evaluated every 20ms. If the voltage deviation is still greater than 3% after three consecutive adjustments, Kcorr1 is switched to Kcorr2 to accelerate the convergence speed.

[0079] This invention, by determining the deviation amount and adopting different correction strategies according to different deviation conditions, can more accurately adaptively correct the voltage of the target converter station. This helps the system voltage to quickly return to the normal range, reduces the impact of voltage fluctuations on the stable operation of the system, and improves the voltage stability of the entire multi-terminal cascaded DC system. The voltage allocation coefficient is determined based on the voltage reference value and the deviation amount. This adaptive correction method can better coordinate the power allocation between converter stations and avoid a series of problems caused by unreasonable power allocation due to voltage deviation. This scheme can take different correction measures according to different deviation conditions (first deviation condition and second deviation condition), enabling the system to adapt to various complex operating conditions and external interferences. Whether it is a small voltage fluctuation or a large voltage deviation, it can be effectively adjusted through the corresponding correction strategy, improving the system's adaptability to different operating conditions.

[0080] In one embodiment, the step of performing voltage adaptive correction and current imbalance compensation on the voltage reference value of the target converter station based on the deviation to obtain the voltage adjustment value further includes:

[0081] If it is determined that there are two adjacent target converter stations, the DC current cross-coupling coefficient is determined based on the voltage distribution coefficient of the adjacent target converter stations.

[0082] Based on the DC current cross-coupling coefficient and the actual port voltage, the voltage correction value of the target converter station is compensated for current imbalance to obtain the voltage adjustment value.

[0083] Specifically, cascaded converter stations typically have the same series current. When inter-station communication detects a difference in the current of the cascaded converter stations, indicating that two target converter stations are adjacent, it is necessary to adjust the voltage commands of the adjacent converter stations. To avoid unbalanced control of the converter stations, this invention simultaneously introduces a DC current cross-coupling term. That is, the DC current cross-coupling coefficient is determined based on the voltage distribution coefficient of the adjacent target converter stations, and it is expressed by the following formula:

[0084] kcouple=αi×(Rd1+Rd2+···+Rd(n-1))

[0085] In the formula, kcouple is the DC current cross-coupling coefficient.

[0086] Next, based on the calculated DC current cross-coupling coefficient and its corresponding actual port voltage, current imbalance compensation is applied to the voltage correction value of the target converter station to obtain the voltage adjustment value, which is expressed by the following formula:

[0087] Udiref=Ud+kcouple×(Id-Idref)

[0088] In the formula, Id is the DC current; Idref is the loop reference current, that is, the reference current value.

[0089] The voltage reference value obtained after the above current correction is used as the voltage adjustment value for the converter station. By compensating for current differences between different converter stations, current fluctuations caused by voltage adjustment are offset, thus avoiding the emergence of new imbalance points.

[0090] This invention determines the DC current cross-coupling coefficient based on the voltage distribution coefficient of adjacent target converter stations, and uses this coefficient to compensate for current imbalance in the voltage correction value. This effectively suppresses the adverse effects of this cross-coupling effect, reduces voltage and current fluctuations in the system, and thus improves the stability of the entire system. Current imbalance affects the power distribution between converter stations. After using the above scheme to compensate for current imbalance, each converter station can accurately distribute power according to the expected voltage distribution coefficient, avoiding uneven power distribution caused by current imbalance, improving the accuracy and rationality of power distribution, and ensuring efficient system operation. This scheme can dynamically adjust the voltage correction value according to the actual situation of adjacent converter stations, adapting to different operating conditions and load changes, and enhancing the system's adaptability to various complex operating conditions.

[0091] In one embodiment, the method further includes:

[0092] The required power of the multi-terminal cascaded DC system is obtained and combined with the cascade resistance and rated DC voltage reference value of each cascaded converter station to quantify the base current of each cascaded converter station.

[0093] The voltage equalization gain of each cascaded converter station is collected and combined with its deviation to quantify the correction current of each cascaded converter station.

[0094] The historical average current of each cascaded converter station is collected and combined with its real-time resistance value to quantify the impedance compensation current of each cascaded converter station.

[0095] The base current, correction current and impedance compensation current of each cascaded converter station are combined and subjected to amplitude limiting to obtain the reference current value of each cascaded converter station.

[0096] Specifically, this invention quantifies the reference current value of the converter station from three aspects: system power demand, voltage balancing strategy, and cascaded topology characteristics, including:

[0097] The required power of the multi-terminal cascaded DC system is obtained and combined with the cascade resistance and rated DC voltage reference values ​​of each cascaded converter station to quantify the base current of each cascaded converter station, which is expressed by the following formula:

[0098] Idref-base=Porder / (η*Udtotal)

[0099]

[0100] In the formula, Idref-base is the base current; Porder is the demand power, i.e. the total power command issued by the dispatcher; η is the system efficiency coefficient (typical value 0.98); Udtotal is the total system voltage; Udirefi is the reference value of the rated DC voltage of the i-th converter station; Idavg is the historical average current; Rk is the cascade resistance, which can also be understood as the line resistance.

[0101] The voltage equalization gain of each level of converter station is collected and combined with its deviation to quantify the correction current of each level of converter station, which is expressed by the following formula:

[0102]

[0103] In the formula, ΔIdref is the correction current; Kv is the voltage equalization gain (preferably 0.2pu); and Udavg is the historical average voltage.

[0104] Historical average current values ​​of each level of converter station are collected and combined with their real-time resistance values ​​to quantify the impedance compensation current of each level of converter station, which is expressed by the following formula:

[0105] ΔIdR=Idhist*Σ△R(n-1) / ΣRk

[0106] In the formula, ΔIdR is the impedance compensation current; Idhist is the historical average current.

[0107] Finally, the base current, correction current, and impedance compensation current of each cascaded converter station are added together, and the sum is then subjected to amplitude limiting processing to obtain the reference current value of the cascaded converter station. The amplitude limiting processing includes: comparing the reference current value with the first current and the second current; if the reference current value is less than the first current, the first current (0.1 times the rated DC current, minimum operating current) is used as the reference current value; if the reference current value is greater than the second current, the second current (1.1 times the rated DC current, overcurrent protection threshold) is used as the reference current value; if it is between the first current and the second current, the current itself is used.

[0108] This invention acquires the required power of a multi-terminal cascaded DC system and quantifies the base current by combining the cascade resistance and rated DC voltage reference values. Based on the actual system requirements and the characteristics of each converter station, it can achieve a preliminary and reasonable power allocation among the converter stations, providing a foundation for subsequent precise control. Collecting voltage balancing gain and deviation values ​​to quantify the correction current effectively compensates for voltage imbalances caused by various factors, maintaining a relatively balanced voltage across converter stations, improving system stability and reliability, and reducing equipment failures and performance degradation caused by voltage imbalances. Collecting historical current averages and real-time resistance values ​​to quantify the impedance compensation current takes into account dynamic changes during system operation, ensuring that the current reference values ​​of the converter stations can adapt to these changes in a timely manner, guaranteeing stable system operation under different operating conditions. Limiting the combined current prevents it from exceeding the current tolerance of the converter stations and lines, avoiding equipment damage and system collapse due to overcurrent, and improving system safety and robustness.

[0109] S4. The voltage adjustment value of the target converter station and the voltage reference value of the other cascaded converter stations are respectively sent to each of the cascaded converter stations to control each of the cascaded converter stations to generate and execute the firing angle command through the PI algorithm according to its own cascaded control mode, so as to realize the control of the multi-terminal cascaded DC system.

[0110] Specifically, this invention designs a control architecture comprising an outer layer and an inner layer to achieve orderly generation and balanced distribution of control quantities. The converter station control strategy is divided into an inner-layer converter station control layer and an outer-layer collaborative control layer, based on reference value generation and control. The inner-layer converter station control layer includes an independent voltage and current closed-loop controller for each converter station, employing a proportional-integral (PI) algorithm and collecting real-time data on voltage, current, and line impedance from all converter stations. The outer-layer collaborative control layer receives data collected by the inner-layer converter station control layer via a newly added high-speed fiber optic communication network (100 Mbps communication), and designs voltage distribution coefficients based on droop characteristics. The inner-layer converter station control layer then uniformly distributes voltage reference values ​​to multiple converter stations.

[0111] In the design of the control layer of the bottom converter station, the current control strategy of each converter station should be fully considered. In conventional end-to-end projects, the sending end rectifier side generally adopts a constant current control strategy. When the constant current cannot meet the requirements, it will switch to constant DC voltage control. When there are multiple converter stations cascaded, the control strategies between the converter stations should be allocated in advance, that is, the control combination mode of the sending end cascaded converter stations should be determined.

[0112] In one embodiment, the cascaded control mode includes a first control mode and a second control mode; the first control mode uses constant current control for all sending-end converter stations; the second control mode uses constant voltage control for at least one sending-end converter station and constant current control for the rest; wherein,

[0113] The step of controlling each of the cascaded converter stations to generate a firing angle command using a PI algorithm according to its own cascaded control mode includes:

[0114] When the cascaded converter station adopts the first control mode, the difference between the DC current of the cascaded converter station and its reference current value is used as input, processed by the PI controller and the limiting circuit, and the firing angle command is output.

[0115] When the cascaded converter station adopts the second control mode, the difference between the actual port voltage of the cascaded converter station and its voltage adjustment value is used as input, processed by the PI controller and the limiting circuit, and the trigger angle command is output.

[0116] Specifically, referring to the end-to-end control strategy, multiple converter stations can choose either constant current or constant voltage control. Taking N cascaded converter stations as an example, the possible combinations of control modes for the sending-end cascaded converter stations include the first control mode: all sending-end converter stations adopt constant current control, and the second control mode: at least one sending-end converter station adopts constant DC voltage control.

[0117] When the converter station adopts the first control mode, the difference between the DC current of the cascaded converter station and its reference current value is used as the input. The PI controller processes the input signal according to the preset proportional coefficient and integral coefficient (the preset coefficients in the PI controller can also be set according to historical data or expert experience, and no specific numerical limit is given here), and calculates the control quantity. The control quantity is processed by the limiting circuit (the upper limit angle and the lower limit angle are set according to historical data or expert experience. When the control quantity is less than the lower limit angle, the lower limit angle is used as the trigger angle; when the control quantity is greater than the upper limit angle, the upper limit angle is used as the trigger angle; if it is in between, the upper limit angle is used as the trigger angle). This limits its output range to a reasonable trigger angle range. The final output trigger angle command is between 12.5 and 17.5 degrees to control the trigger pulse of the cascaded converter station, thereby regulating the DC current. The receiving end adopts constant voltage control or constant angle control.

[0118] When the converter station adopts the second control mode, the difference between the actual port voltage of the cascaded converter station and its voltage adjustment value is used as the input. The PI controller processes the input signal according to the preset proportional and integral coefficients to calculate the control quantity. The control quantity is processed by a limiting circuit (the principle is the same as above) to limit its output range to a reasonable firing angle range, and finally outputs a firing angle command to control the firing pulse of the cascaded converter station, thereby regulating the DC current. The receiving end adopts constant voltage control or constant angle control.

[0119] This invention employs two different cascaded control modes, which can flexibly adjust voltage and current according to the actual operating requirements of the system. This better maintains system voltage stability and improves the stability and reliability of the entire cascaded converter station system when the system load changes or a fault occurs. Simultaneously, the two control modes can be switched or combined according to different operating conditions, enabling the system to adapt to various complex operating environments and improving control flexibility and adaptability. By generating trigger angle commands through a PI algorithm, the actual current or voltage of the cascaded converter station is made to track the reference value as quickly as possible, reducing system overshoot and oscillation, thereby optimizing the overall system performance and improving the quality and efficiency of power transmission.

[0120] Taking an ultra-high voltage three-terminal DC project as an example, its DC voltage is ±800kV, with two cascaded converter stations 1 and 2 at the sending end, both with AC system voltages of 500-550kV. The AC system voltage at converter station 3 at the receiving end is also 500-550kV. The DC power is 8000MW, and the rated DC current is 5kA. After setting converter station voltage weights and adopting the control strategy described in the first aspect of this invention, the effectiveness of this invention is verified under typical operating conditions such as step response, AC fault, DC line fault restart, in-station fault blocking, and power transfer. The power step result diagram is shown below. Figure 2 As shown in the figure, the current step result is as follows: Figure 3 As shown in the figure, the result diagram of the DC line fault is as follows. Figure 4 As shown in the diagram, the AC line fault result is as follows: Figure 5 As shown in the figure, the current + voltage loop changes after a valve short circuit in a certain converter station are as follows: Figure 6 As shown, by Figure 2-6 It can be seen that a power step of 1 pu and a lower step of 0.1 pu have a response time of 196 ms and an overshoot of 31%; a current step of 0.92 pu and an upper step of 0.08 pu have a response time of 190 ms and an overshoot of 2.5%; a power recovery time of 140 ms for a DC line fault from the sending end to the receiving end; and a power recovery time of 145 ms for a single-phase ground fault on the high end of the receiving end converter station 1. Therefore, it is evident that after adopting the method described in this invention, multi-terminal cascaded converter stations can still ensure normal DC operation under steady-state conditions even with current + voltage loop faults. Simultaneously, it achieves comprehensive improvements in dynamic response speed, stability, fault recovery capability, and multi-condition adaptability, making it particularly suitable for complex DC systems with high voltage, large capacity, and multi-terminal cascade.

[0121] This application addresses the issue of how to provide a control strategy for multi-terminal cascaded DC systems when DC voltage is unbalanced, ensuring stable system operation and excellent control characteristics, and achieving safe and reliable power transmission. A control method for multi-terminal cascaded DC systems is designed. This method dynamically determines static and dynamic droop coefficients by acquiring real-time operating data and conditions of all cascaded converter stations. This allows for more accurate quantification of the voltage reference values ​​of each converter station, effectively responding to various operating condition changes, enhancing system stability in complex environments, and reducing the risk of system instability due to fixed parameters. By performing voltage adaptive correction and current imbalance compensation on converter stations with deviations, the output voltage of each converter station meets system requirements, improving the voltage control accuracy of the entire multi-terminal cascaded DC system and ensuring power quality. The use of a control method based on precise parameters and adaptive adjustment optimizes the control effect, enabling efficient and stable control under various operating conditions, reducing energy loss, improving system operating efficiency, and ensuring that the system can accurately and flexibly adjust the control strategy of the converter stations under different operating modes. This ensures that the multi-terminal cascaded DC transmission system has reliable operation and excellent response characteristics, achieving safe and reliable power transmission.

[0122] It should be noted that although the steps in the flowchart above are shown sequentially as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order requirement for the execution of these steps, and they can be executed in other orders.

[0123] In another embodiment, such as Figure 7 As shown, a second aspect of the present invention provides a control device for a multi-terminal cascaded DC system, comprising:

[0124] The data acquisition module 10 is used to acquire real-time operating data and real-time operating conditions of all cascaded converter stations in the multi-terminal cascaded DC system.

[0125] The voltage quantization module 20 is used to determine the static droop coefficient and dynamic droop coefficient of each cascaded converter station based on the real-time operating conditions, so as to combine with the real-time operating data to quantify the voltage reference value of each cascaded converter station.

[0126] The voltage adjustment module 30 is used to quantify the actual port voltage of each cascaded converter station, so as to take the cascaded converter station with deviation as the target converter station, and perform voltage adaptive correction and current imbalance compensation on the voltage reference value of the target converter station according to the deviation to obtain the voltage adjustment value.

[0127] The instruction execution module 40 is used to send the voltage adjustment value of the target converter station and the voltage reference value of the other cascaded converter stations to each of the cascaded converter stations, so as to control each of the cascaded converter stations to generate and execute the trigger angle instruction through the PI algorithm according to its own cascaded control mode, so as to realize the control of the multi-terminal cascaded DC system.

[0128] It should be noted that each module in the aforementioned control device for a multi-terminal cascaded DC system can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device, or stored in the memory of a computer device as software, so that the processor can call and execute the operations corresponding to each module. For specific limitations regarding the control device for a multi-terminal cascaded DC system, please refer to the limitations of the control method for a multi-terminal cascaded DC system described above; both have the same function and role, and will not be repeated here.

[0129] A third aspect of the present invention provides an electronic device comprising:

[0130] Processor, memory, and bus;

[0131] The bus is used to connect the processor and the memory;

[0132] The memory is used to store operation instructions;

[0133] The processor is configured to execute instructions by calling the operation instructions, causing the processor to perform operations corresponding to a control method for a multi-terminal cascaded DC system as shown in the first aspect of this application.

[0134] In one alternative embodiment, an electronic device is provided, such as Figure 8 As shown, Figure 8 The illustrated electronic device 5000 includes a processor 5001 and a memory 5003. The processor 5001 and the memory 5003 are connected, for example, via a bus 5002. Optionally, the electronic device 5000 may also include a transceiver 5004. It should be noted that in practical applications, the transceiver 5004 is not limited to one type, and the structure of this electronic device 5000 does not constitute a limitation on the embodiments of this application.

[0135] Processor 5001 may be a CPU, a general-purpose processor, a DSP, an ASIC, an FPGA, or other programmable logic device, transistor logic device, hardware component, or any combination thereof. It may implement or execute the various exemplary logic blocks, modules, and circuits described in conjunction with the disclosure of this application. Processor 5001 may also be a combination that implements computational functions, such as including one or more microprocessor combinations, a combination of a DSP and a microprocessor, etc.

[0136] Bus 5002 may include a path for transmitting information between the aforementioned components. Bus 5002 may be a PCI bus or an EISA bus, etc. Bus 5002 can be divided into address bus, data bus, control bus, etc. For ease of representation, Figure 8 The bus is represented by a single thick line, but this does not mean that there is only one bus or one type of bus.

[0137] The memory 5003 may be a ROM or other type of static storage device capable of storing static information and instructions, RAM or other type of dynamic storage device capable of storing information and instructions, or it may be an EEPROM, CD-ROM or other optical disc storage, optical disc storage (including compressed optical discs, laser discs, optical discs, digital universal optical discs, Blu-ray discs, etc.), magnetic disk storage media or other magnetic storage devices, or any other medium capable of carrying or storing desired program code in the form of instructions or data structures and accessible by a computer, but is not limited thereto.

[0138] The memory 5003 is used to store application code that executes the scheme of this application, and its execution is controlled by the processor 5001. The processor 5001 is used to execute the application code stored in the memory 5003 to implement the content shown in any of the foregoing method embodiments.

[0139] Among them, electronic devices include, but are not limited to: mobile terminals such as mobile phones, laptops, digital radio receivers, PDAs (personal digital assistants), PADs (tablet computers), PMPs (portable multimedia players), and in-vehicle terminals (such as in-vehicle navigation terminals), as well as fixed terminals such as digital TVs and desktop computers.

[0140] The fourth aspect of the present invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements a control method for a multi-terminal cascaded DC system as shown in the first aspect of the present application.

[0141] Another embodiment of this application provides a computer-readable storage medium storing a computer program that, when run on a computer, enables the computer to execute the corresponding content in the aforementioned method embodiments.

[0142] Furthermore, embodiments of the present invention also provide a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-described method.

[0143] In summary, this invention relates to the field of power transmission system technology, and discloses a control method, device, equipment, and medium for multi-terminal cascaded DC systems. The method includes acquiring real-time operating data of cascaded converter stations in a multi-terminal cascaded DC system to determine the droop coefficient of each cascaded converter station under different operating conditions, thereby quantifying its voltage reference value; calculating the port voltage of each cascaded converter station, and performing voltage adaptive correction and current imbalance compensation on the voltage reference value of the cascaded converter stations based on the deviation between the port voltage and the voltage reference value, obtaining a voltage adjustment value which is then sent to the corresponding cascaded converter station. This allows the station to control the multi-terminal cascaded DC system by generating and executing a firing angle command through a PI algorithm according to its own cascaded control mode. This effectively solves the DC voltage imbalance problem in multi-terminal cascaded DC systems, thereby ensuring stable system operation and excellent control characteristics, and achieving safe and reliable power transmission from the DC system.

[0144] The various embodiments in this specification are described in a progressive manner. For directly identical or similar parts of the embodiments, refer to each other. Each embodiment focuses on its differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. It should be noted that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification.

[0145] The embodiments described above are merely preferred embodiments of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various improvements and substitutions without departing from the technical principles of this invention, and these improvements and substitutions should also be considered within the scope of protection of this application. Therefore, the scope of protection of this patent application should be determined by the scope of the claims.

Claims

1. A control method for a multi-terminal cascaded DC system, characterized in that, include: To acquire real-time operating data and operating conditions of all cascaded converter stations in a multi-terminal cascaded DC system; The real-time operating data includes DC current; Based on the real-time operating conditions, the static droop coefficient and dynamic droop coefficient of each cascaded converter station are determined, and combined with the real-time operating data to quantify the voltage reference value of each cascaded converter station. This includes: determining the operating converter stations in the multi-terminal cascaded DC system based on the real-time operating conditions, and determining the static droop coefficient based on the rated equivalent resistance of the operating converter station; acquiring real-time environmental data for each operating converter station, and constructing an environmental resistance model based on the real-time environmental data to quantify the real-time resistance value of each operating converter station; determining the dynamic droop coefficient of each operating converter station based on its real-time resistance value; acquiring the rated DC voltage reference value and rated current of each cascaded converter station, and combining them with the DC current, the static droop coefficient, and the dynamic droop coefficient to quantify the voltage reference value of each cascaded converter station; wherein, the static droop coefficient is expressed by the following formula: ki=(RN1+RN2+···+RN(n-1)) / n In the formula, ki is the static droop coefficient of the i-th cascaded converter station, i=n-1; RN(n-1) is the rated equivalent resistance between the (n-1)-th cascaded converter station and the n-th cascaded converter station; n is the number of cascaded converter stations in the multi-terminal cascaded DC system. The dynamic droop coefficient is expressed by the following formula: kj=(△R1+△R2+···+△R(n-1)) / n In the formula, kj is the dynamic droop coefficient, where j=n-1; △R(n-1) is the resistance change of the connection line between the (n-1)th cascade converter station and the nth cascade converter station; The actual port voltage of each cascaded converter station is quantified, and the cascaded converter station with deviation is taken as the target converter station. The voltage reference value of the target converter station is then adaptively corrected and the current imbalance is compensated based on the deviation to obtain the voltage adjustment value. The voltage adjustment value of the target converter station and the voltage reference values ​​of the other cascaded converter stations are respectively sent to each of the cascaded converter stations to control each of the cascaded converter stations to generate and execute firing angle commands through a PI algorithm according to its own cascaded control mode, so as to realize the control of the multi-terminal cascaded DC system.

2. The control method for a multi-terminal cascaded DC system according to claim 1, characterized in that, The quantification of the actual port voltage of each of the cascaded converter stations includes: The inter-station line lengths of each of the cascaded converter stations are obtained to quantify the line resistance of each of the cascaded converter stations. The line resistance of the multi-terminal cascaded DC system is determined based on the line resistance of each of the aforementioned lines, and combined with the DC current of each of the cascaded converter stations to determine the actual port voltage of each of the cascaded converter stations.

3. The control method for a multi-terminal cascaded DC system according to claim 1, characterized in that, The step of performing voltage adaptive correction and current imbalance compensation on the voltage reference value of the target converter station based on the deviation to obtain the voltage adjustment value includes: When it is determined that the deviation meets the first deviation condition, the first correction gain is determined based on the deviation, and the voltage distribution coefficient of the target converter station is determined in combination with the voltage reference value of the target converter station to perform voltage adaptive correction and obtain the voltage correction value. When the deviation is determined to meet the second deviation condition, the second correction gain is determined based on the deviation, and the voltage distribution coefficient of the target converter station is determined in combination with the voltage reference value of the target converter station to perform voltage adaptive correction and obtain the voltage correction value.

4. The control method for a multi-terminal cascaded DC system according to claim 3, characterized in that, The step of performing voltage adaptive correction and current imbalance compensation on the voltage reference value of the target converter station based on the deviation to obtain the voltage adjustment value also includes: If it is determined that there are two adjacent target converter stations, the DC current cross-coupling coefficient is determined based on the voltage distribution coefficient of the adjacent target converter stations. Based on the DC current cross-coupling coefficient and the actual port voltage, the voltage correction value of the target converter station is compensated for current imbalance to obtain the voltage adjustment value.

5. A control method for a multi-terminal cascaded DC system according to claim 2, characterized in that, The cascaded control mode includes a first control mode and a second control mode; the first control mode uses constant current control for all sending-end converter stations; the second control mode uses constant voltage control for at least one sending-end converter station, and constant current control for the rest; wherein... The step of controlling each of the cascaded converter stations to generate a firing angle command using a PI algorithm according to its own cascaded control mode includes: When the cascaded converter station adopts the first control mode, the difference between the DC current of the cascaded converter station and its reference current value is used as input, processed by the PI controller and the limiting circuit, and the firing angle command is output. When the cascaded converter station adopts the second control mode, the difference between the actual port voltage of the cascaded converter station and its voltage adjustment value is used as input, processed by the PI controller and the limiting circuit, and the trigger angle command is output.

6. The control method for a multi-terminal cascaded DC system according to claim 5, characterized in that, The method further includes: The required power of the multi-terminal cascaded DC system is obtained and combined with the cascade resistance and rated DC voltage reference value of each cascaded converter station to quantify the base current of each cascaded converter station. The voltage equalization gain of each cascaded converter station is collected and combined with its deviation to quantify the correction current of each cascaded converter station. The historical average current of each cascaded converter station is collected and combined with its real-time resistance value to quantify the impedance compensation current of each cascaded converter station. The base current, correction current and impedance compensation current of each cascaded converter station are combined and subjected to amplitude limiting to obtain the reference current value of each cascaded converter station.

7. A control device for a multi-terminal cascaded DC system, characterized in that, include: The data acquisition module is used to acquire real-time operating data and real-time operating conditions of all cascaded converter stations in a multi-terminal cascaded DC system. The real-time operating data includes DC current; A voltage quantization module is used to determine the static droop coefficient and dynamic droop coefficient of each cascaded converter station based on the real-time operating conditions, and to combine them with the real-time operating data to quantify the voltage reference value of each cascaded converter station. This includes: determining the operating converter stations in the multi-terminal cascaded DC system based on the real-time operating conditions, and determining the static droop coefficient based on the rated equivalent resistance of the operating converter station; acquiring real-time environmental data of each operating converter station, and constructing an environmental resistance model based on the real-time environmental data to quantify the real-time resistance value of each operating converter station; determining the dynamic droop coefficient of each operating converter station based on its real-time resistance value; and acquiring the rated DC voltage reference value and rated current of each cascaded converter station, and combining them with the DC current, the static droop coefficient, and the dynamic droop coefficient to quantize the voltage reference value of each cascaded converter station. The static droop coefficient is expressed by the following formula: ki=(RN1+RN2+···+RN(n-1)) / n In the formula, ki is the static droop coefficient of the i-th cascaded converter station, i=n-1; RN(n-1) is the rated equivalent resistance between the (n-1)-th cascaded converter station and the n-th cascaded converter station; n is the number of cascaded converter stations in the multi-terminal cascaded DC system. The dynamic droop coefficient is expressed by the following formula: kj=(△R1+△R2+···+△R(n-1)) / n In the formula, kj is the dynamic droop coefficient, where j=n-1; △R(n-1) is the resistance change of the connection line between the (n-1)th cascade converter station and the nth cascade converter station; The voltage adjustment module is used to quantify the actual port voltage of each cascaded converter station, so as to take the cascaded converter station with deviation as the target converter station, and perform voltage adaptive correction and current imbalance compensation on the voltage reference value of the target converter station according to the deviation to obtain the voltage adjustment value. The instruction execution module is used to send the voltage adjustment value of the target converter station and the voltage reference value of the other cascaded converter stations to each of the cascaded converter stations, so as to control each of the cascaded converter stations to generate and execute the trigger angle instruction through the PI algorithm according to its own cascaded control mode, so as to realize the control of the multi-terminal cascaded DC system.

8. An electronic device, characterized in that, The system includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein the processor, when executing the computer program, implements the control method for a multi-terminal cascaded DC system as described in any one of claims 1 to 6.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored computer program, wherein when the device containing the computer-readable storage medium executes the computer program, it implements the control method for a multi-terminal cascaded DC system as described in any one of claims 1 to 6.

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