Multi-terminal hybrid DC transmission system and its adaptive droop control method and device

Abstract

This invention discloses a multi-terminal hybrid DC transmission system and its adaptive droop control method and apparatus. The method includes: determining the cumulative total output power variation of each MMC converter in the multi-terminal hybrid DC transmission system; obtaining the system's rated DC current, measured DC current, droop characteristic coefficient of any MMC converter, and rated DC voltage; calculating the DC voltage compensation amount for any MMC converter based on the system's rated DC current, measured DC current, droop characteristic coefficient of any MMC converter, and rated DC voltage; and using the DC voltage compensation amount of any MMC converter, compensating for the cumulative total output power variation of each MMC converter based on the droop control characteristics. By introducing the DC voltage compensation amount, adaptive adjustment is performed in real time according to changes in the system's DC current, avoiding deviations in DC voltage caused by changes in DC current, maintaining the DC voltage at the rated reference value, improving the system voltage stability, and is simple and easy to implement.

Description

Technical Field

[0001] This invention relates to the field of control technology for multi-terminal hybrid DC transmission systems, and specifically to a multi-terminal hybrid DC transmission system and its adaptive droop control method and device. Background Technology

[0002] With the rapid development of power electronics technology, direct current (DC) transmission systems have been widely applied. These DC transmission systems mainly include high-voltage direct current (LCC-HVDC), flexible direct current (VSC-HVDC), and hybrid DC transmission systems. Among them, hybrid DC transmission systems combine the advantages of both LCC-HVDC and VSC-HVDC systems and have become an important development direction for DC transmission technology in recent years.

[0003] In hybrid DC transmission systems, the receiving-end MMC converter station, consisting of multiple MMC converters connected in parallel and then cascaded with LCC converters, effectively forms a multi-terminal structure, endowing multiple MMC inverter stations with power distribution capabilities. However, the active power distribution strategy of multiple MMC converters needs to coordinate with the active power commands of the sending-end LCC converter; otherwise, unreasonable power coordination among stations will occur. Low-end MMCs can employ master-slave control under single-point DC voltage control. However, MMCs using single-point DC voltage control lack the ability to control DC power. On one hand, when a fault occurs on the receiving-end AC side, the MMCs generally exhibit power backfeeding, and current imbalances may occur among multiple parallel MMCs, ultimately leading to overcurrent. On the other hand, if a single-point DC voltage controlled MMC converter fails and is locked out, the system will be unable to control the overall DC voltage.

[0004] To address the problems associated with single-point DC voltage control in hybrid DC transmission systems, a droop control method for multi-terminal hybrid DC transmission systems was further introduced. This method can simultaneously control both the overall DC voltage and DC power. However, when the DC current of the hybrid DC transmission system fluctuates, the DC voltage of the MMC converter using droop control will also deviate with the increase or decrease of the system DC current, resulting in inaccurate DC voltage control. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to solve the problem that when the DC current of a hybrid DC transmission system fluctuates by increasing or decreasing, the DC voltage of the MMC converter using droop control will also deviate with the increase or decrease of the system DC current, resulting in the inability to accurately control the DC voltage. Thus, the present invention provides a multi-terminal hybrid DC transmission system and its adaptive droop control method and device.

[0006] According to a first aspect, embodiments of the present invention provide an adaptive droop control method for a multi-terminal hybrid DC transmission system, comprising the following steps:

[0007] Determine the cumulative total output power variation of each MMC converter in a multi-terminal hybrid DC transmission system;

[0008] Obtain the rated DC current, measured DC current, droop characteristic coefficient, and rated DC voltage of any MMC converter in a multi-terminal hybrid DC transmission system;

[0009] Based on the rated DC current, measured DC current, droop characteristic coefficient and rated DC voltage of any MMC converter in the multi-terminal hybrid DC transmission system, calculate the DC voltage compensation of any MMC converter.

[0010] The DC voltage compensation of any MMC converter is used to compensate for the cumulative total output power variation of each MMC converter based on the droop control characteristics.

[0011] In one embodiment, the DC voltage compensation of any MMC converter is calculated based on the rated DC current of the multi-terminal hybrid DC transmission system, the measured DC current, the droop characteristic coefficient of any MMC converter, and the rated DC voltage of any MMC converter, using the following formula:

[0012]

[0013] Where, m j I is the DC voltage compensation amount for the j-th MMC converter. dcref I is the rated value of the DC current. dc U is the measured DC voltage value. dcref K represents the DC voltage rating of any MMC converter. drop_i Let be the droop characteristic coefficient of the i-th MMC converter, and n be the total number of MMC converters.

[0014] In one implementation, using the DC voltage compensation amount of any of the MMC converters, the compensation for the cumulative total output power variation of each MMC converter based on the droop control characteristics includes:

[0015] The rated DC current and the measured DC current of the multi-terminal hybrid DC transmission system satisfy the following formula:

[0016]

[0017] Among them, I dcref I is the rated DC current of the multi-terminal hybrid DC transmission system. dcThe measured value of the DC current in the multi-terminal hybrid DC transmission system;

[0018] Based on the droop control characteristics, the DC voltage compensation amount is controlled to be equal to a preset value.

[0019] In one embodiment, using the DC voltage compensation amount of any of the MMC converters, the compensation for the cumulative total output power variation of each MMC converter based on the droop control characteristics further includes:

[0020] If the DC voltage compensation of any MMC converter is equal to a preset value, the droop characteristic line is kept stationary.

[0021] If the DC voltage compensation of any MMC converter is greater than the preset value, the droop characteristic line is controlled to move in the first direction.

[0022] If the DC voltage compensation of any of the MMC converters is less than a preset value, the droop characteristic line is controlled to move in the second direction.

[0023] In one implementation, the droop control characteristic satisfies the following formula:

[0024] P mj -P refj +K drop_j (U dcref -U dc ) = 0;

[0025] Among them, P mj Let P be the current output power of the j-th MMC converter. refj K represents the rated output power of the j-th MMC converter. drop_j U is the droop characteristic coefficient of the j-th MMC converter. dcref U is the DC voltage rating of any MMC converter. dc This represents the measured DC voltage value for any MMC converter.

[0026] In one implementation, the DC voltage measurement of any of the MMC converters is kept stable by the following formula:

[0027]

[0028] Among them, U dc P represents the measured DC voltage value of any MMC converter. mj Let P be the current output power of the j-th MMC converter. refj K represents the rated output power of the j-th MMC converter. drop_j U is the droop characteristic coefficient of the j-th MMC converter. dcref Let m be the DC voltage rating of any MMC converter.j DC voltage compensation for the j-th MMC converter.

[0029] In one implementation, the DC voltage measurement of any of the MMC converters is kept stable in the following manner:

[0030] Obtain the droop characteristic line of the multi-terminal hybrid DC transmission system as a result of the change in total output power;

[0031] Determine the coordinates (P) of any point on the drooping characteristic line that ensures the stability of the DC voltage measurement value for any MMC converter. mj U dcref ).

[0032] In one implementation, determining the cumulative total output power variation of each MMC converter in the multi-terminal hybrid converter DC transmission system includes:

[0033] Obtain the current output power and rated output power of any MMC converter;

[0034] The output power deviation of any MMC converter is obtained by calculating the difference between its current output power and rated output power.

[0035] Based on the output power deviation of any MMC converter, calculate the cumulative total output power change of each MMC converter.

[0036] According to a second aspect, embodiments of the present invention provide an adaptive droop control device for a multi-terminal hybrid DC transmission system, comprising the following modules:

[0037] The total power change determination module is used to determine the cumulative total output power change of each MMC converter in a multi-terminal hybrid DC transmission system.

[0038] The parameter acquisition module is used to acquire the rated DC current, measured DC current, droop characteristic coefficient of any MMC converter, and rated DC voltage of the multi-terminal hybrid DC transmission system.

[0039] The DC voltage compensation calculation module is used to calculate the DC voltage compensation of any MMC converter based on the rated DC current, measured DC current, droop characteristic coefficient and rated DC voltage of the multi-terminal hybrid DC transmission system.

[0040] The compensation module is used to compensate for the cumulative total output power variation of each MMC converter based on the droop control characteristics by utilizing the DC voltage compensation amount of any of the MMC converters.

[0041] According to a third aspect, embodiments of the present invention provide a multi-terminal hybrid DC transmission system for the adaptive droop control method described in the first aspect or any embodiment of the first aspect, comprising:

[0042] Sending end AC power grid;

[0043] The rectifier station includes multiple sets of LCC converters, each set of LCC converters being connected to the sending-end AC power grid.

[0044] An inverter station includes at least one set of LCC converters and multiple parallel MMC converters. The input terminals of the at least one set of LCC converters are connected to the rectifier station, and the output terminals of the at least one set of LCC converters are connected to the multiple parallel MMC converters.

[0045] A DC filter is connected to both the rectifier station and the inverter station.

[0046] The receiving-end AC grid includes multiple AC ports distributed in parallel, each AC port being connected to its corresponding MMC converter.

[0047] According to a fourth aspect, embodiments of the present invention provide a computer-readable storage medium storing computer instructions for causing the computer to perform the adaptive droop control method described in the first aspect or any embodiment of the first aspect.

[0048] According to a fifth aspect, an embodiment of the present invention provides an electronic device, comprising: a multi-terminal hybrid DC transmission system as described in the third aspect, a memory, and a processor, wherein the multi-terminal hybrid DC transmission system, the memory, and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the computer instructions to perform the adaptive droop control method as described in the first aspect or any embodiment of the first aspect.

[0049] The technical solution of this invention has the following advantages:

[0050] This invention discloses a multi-terminal hybrid DC transmission system and its adaptive droop control method and apparatus. The method includes: determining the cumulative total output power variation of each MMC converter in the multi-terminal hybrid DC transmission system; acquiring the system's rated DC current, measured DC current, droop characteristic coefficient of any MMC converter, and rated DC voltage; calculating the DC voltage compensation amount of any MMC converter based on the system's rated DC current, measured DC current, droop characteristic coefficient of any MMC converter, and rated DC voltage; and using the DC voltage compensation amount of any MMC converter to compensate for the cumulative total output power variation of each MMC converter based on the droop control characteristics. On the one hand, it can adaptively adjust the droop characteristics of any MMC converter in real time based on changes in the system's measured DC current, thereby avoiding deviations in DC voltage caused by changes in DC current, maintaining the DC voltage at its rated reference value, improving system voltage stability, and ultimately achieving precise control of the measured DC voltage value of any MMC converter. Simultaneously, it can effectively reduce fluctuations in the measured DC voltage value of any MMC converter during fault periods. On the other hand, any MMC converter using droop control has the ability to control both DC voltage and DC power simultaneously, and there will be no power backfeeding problem. Attached Figure Description

[0051] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0052] Figure 1 This is a schematic diagram of the structure of a multi-terminal hybrid DC transmission system in an embodiment of the present invention;

[0053] Figure 2 This is a flowchart of an adaptive droop control method for a multi-terminal hybrid DC transmission system in an embodiment of the present invention;

[0054] Figure 3A This is a schematic diagram of the droop control characteristics of a multi-terminal hybrid DC transmission system in an embodiment of the present invention;

[0055] Figure 3B This is another schematic diagram of the droop control characteristics of the multi-terminal hybrid DC transmission system in an embodiment of the present invention;

[0056] Figure 4 This is another flowchart of the adaptive droop control method for a multi-terminal hybrid DC transmission system in this embodiment of the invention;

[0057] Figure 5This is a schematic diagram of the adaptive droop control strategy in an embodiment of the present invention;

[0058] Figure 6A This is another schematic diagram of the droop control characteristics of the multi-terminal hybrid DC transmission system in an embodiment of the present invention;

[0059] Figure 6B This is another schematic diagram of the droop control characteristics of the multi-terminal hybrid DC transmission system in an embodiment of the present invention;

[0060] Figure 7A This is a schematic diagram of the DC current at various moments in the multi-terminal hybrid DC transmission system according to an embodiment of the present invention;

[0061] Figure 7B This is a simulation diagram illustrating two scenarios in an embodiment of the present invention: one without adaptive droop control and the other with adaptive droop control.

[0062] Figure 7C This is another simulation diagram illustrating two scenarios in this invention: one without adaptive droop control and one with adaptive droop control.

[0063] Figure 8A This is a schematic diagram of the DC voltage at various moments in the multi-terminal hybrid DC transmission system according to an embodiment of the present invention;

[0064] Figure 8B The following are simulation diagrams illustrating the constant DC voltage master-slave control method and constant power control method used in embodiments of the present invention.

[0065] Figure 9A This is a voltage simulation diagram showing the voltage simulation with and without adaptive control based on the droop control characteristics in an embodiment of the present invention.

[0066] Figure 9B This is a power simulation diagram of the embodiment of the present invention with and without adaptive control based on the droop control characteristics;

[0067] Figure 10 This is a structural block diagram of the adaptive droop control device for a multi-terminal hybrid DC transmission system in an embodiment of the present invention;

[0068] Figure 11 This is a schematic diagram of an electronic device in an embodiment of the present invention. Detailed Implementation

[0069] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0070] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0071] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0072] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0073] This invention relates to the field of control technology for multi-terminal hybrid DC transmission systems, aiming to address the droop control method in related technologies. Because the DC current of the hybrid DC transmission system fluctuates with increases or decreases, the DC voltage of the MMC converter using droop control also deviates, resulting in inaccurate DC voltage control. Therefore, this invention provides a multi-terminal hybrid DC transmission system and its adaptive droop control method and apparatus.

[0074] Example 1

[0075] This invention provides a multi-terminal hybrid DC transmission system, and an adaptive droop control method for the multi-terminal hybrid DC transmission system in this invention embodiment. The system is as follows: Figure 1 As shown, it includes: sending-end AC power grid 11, rectifier station 12, inverter station 13, DC filter 14, and receiving-end AC power grid 15.

[0076] Among them, the sending-end AC power grid 11 is used to provide AC power to the outside world. The sending-end AC power grid 11 can be a synchronous generator or a new energy power generation base.

[0077] The rectifier station 12 includes multiple sets of LCC converters, each set of LCC converters being connected to the sending-end AC power grid 11. For example, the rectifier station can be composed of two sets of 12-pulsating LCC converters connected in series. Voltage transformation can be performed between the rectifier station and the sending-end AC power grid using a transformer.

[0078] Inverter station 13 includes at least one set of LCC converters 131 and multiple parallel MMC converters 132. The input terminals of at least one set of LCC converters 131 are connected to rectifier station 12, and the output terminals of at least one set of LCC converters 131 are connected to multiple parallel MMC converters 132. For example, the inverter station is composed of one set of 12-pulse LCC converters and multiple parallel MMC converters connected in series. The parallel MMC converter group consists of three half-bridge MMC converters connected in parallel.

[0079] The DC filter 14 is connected to the rectifier station 12 and the inverter station 13 respectively, and the DC filter 14 is used to filter the DC power.

[0080] The receiving-end AC power grid 15 includes multiple AC ports distributed in parallel, each AC port being connected to a corresponding MMC converter 132.

[0081] The multi-terminal hybrid DC transmission system in this embodiment of the invention is used in the adaptive droop control method of the multi-terminal hybrid DC transmission system. By introducing a DC voltage compensation amount, the droop characteristics of the MMC converter can be adaptively adjusted in real time according to the changes in the system DC current, avoiding the deviation of DC voltage with changes in DC current, maintaining the DC voltage at the rated reference value, improving the stability of the system voltage, and is simple and easy to implement, which is beneficial to engineering practice.

[0082] Example 2

[0083] This invention provides an adaptive droop control method for a multi-terminal hybrid DC transmission system, applicable to... Figure 1 The multi-terminal hybrid DC transmission system shown in the figure, the method is as follows Figure 2 As shown, it includes the following steps:

[0084] Step S21: Determine the cumulative total output power change of each MMC converter in the multi-terminal hybrid DC transmission system.

[0085] exist Figure 1 As can be seen from the diagram, this multi-terminal hybrid DC transmission system includes multiple parallel-distributed MMC converters on the receiving-end AC grid side. The total output power change here refers to the total active power change output by each MMC converter.

[0086] like Figures 3A-3B As shown, droop control analysis is performed on a multi-terminal hybrid DC transmission system. For example: in Figure 3AIn this system, when the DC current decreases, the total active power of each MMC converter decreases accordingly to P. MMC 'The DC voltage of each MMC converter also decreases accordingly under the action of droop control. For example: in Figure 3B In this system, when the DC current increases, the total active power of each MMC converter increases by P. MMC The DC voltage of each MMC converter also increases accordingly under the action of droop control. Therefore, when the system DC current fluctuates, it will cause the DC voltage to fluctuate, which in turn will result in a cumulative change in the total output power of each MMC converter, ultimately making it impossible to accurately control the DC voltage.

[0087] In one implementation, such as Figure 4 As shown, step S21, which determines the cumulative total output power change of each converter station MMC converter in a multi-terminal hybrid converter DC transmission system, includes:

[0088] Step S211: Obtain the current output power and rated output power of any MMC converter in any converter station.

[0089] For example, a multi-terminal hybrid DC transmission system includes n MMC converters in operation, and the current output power of the j-th MMC converter can be represented by P. mj This means that the rated output power of the j-th MMC converter can be represented by P. refj express.

[0090] Step S212: Calculate the difference between the current output power and the rated output power of any MMC converter to obtain the output power deviation of any MMC converter.

[0091] For example, take the j-th MMC converter as an example. As shown in formula (1):

[0092]

[0093] Wherein, ΔP j Let K be the output power deviation of the j-th MMC converter. drop_j Let ΔP be the droop characteristic coefficient of the j-th MMC converter. MMC K represents the change in total output power. drop_i Let be the droop characteristic coefficient of the i-th MMC converter, and n be the total number of MMC converters.

[0094] Step S213: Calculate the cumulative total output power change of each MMC converter based on the output power deviation of any MMC converter.

[0095] For example, taking the j-th MMC converter or the i-th MMC converter at the converter station as an example, the cumulative change in total output power of the MMC converters at each converter station is shown in the following formula (2):

[0096]

[0097] Wherein, ΔP MMC The change in total output power is ΔP. i Let ΔU be the output power deviation of the i-th MMC converter. dc K represents the total DC voltage rating of each MMC converter. drop_i Let ΔP be the droop characteristic coefficient of the i-th MMC converter, n be the total number of MMC converters, and ΔP be the droop characteristic coefficient. j Let K be the output power deviation of the j-th MMC converter. drop_ Let be the droop characteristic coefficient of the i-th MMC converter.

[0098] Step S22: Obtain the rated DC current, measured DC current, droop characteristic coefficient and rated DC voltage of any MMC converter in the multi-terminal hybrid DC transmission system.

[0099] For example: the DC current rating of a multi-terminal hybrid DC transmission system is represented by I. dcref The DC current measurement value of a multi-terminal hybrid DC transmission system is represented by I. dc The droop characteristic coefficient of any MMC converter can be represented by K. drop_i or K drop_j This indicates that the DC voltage rating of any MMC converter can be expressed as U. dc express.

[0100] Step S23: Calculate the DC voltage compensation of any MMC converter based on the rated DC current, measured DC current, droop characteristic coefficient, and rated DC voltage of the multi-terminal hybrid DC transmission system.

[0101] In one embodiment, step S23, which calculates the DC voltage compensation of any MMC converter based on the rated DC current of the multi-terminal hybrid DC transmission system, the measured DC current, the droop characteristic coefficient of any MMC converter, and the rated DC voltage, is performed by the following formula (3):

[0102]

[0103] Where, m j I is the DC voltage compensation amount for the j-th MMC converter. dcref I is the rated value of DC current. dc This is a DC voltage measurement value, U dcrefK represents the DC voltage rating of any MMC converter. drop_i Let be the droop characteristic coefficient of the i-th MMC converter, and n be the total number of MMC converters. In the above formula (3), the DC voltage compensation m of each MMC converter is equal and is independent of the magnitude of the droop coefficient.

[0104] Step S24: Using the DC voltage compensation of any MMC converter, compensate for the cumulative total output power change of each MMC converter based on the droop control characteristics.

[0105] In one embodiment, step S24, which uses the DC voltage compensation amount of any MMC converter to compensate for the cumulative total output power variation of each MMC converter based on the droop control characteristics, includes:

[0106] Step 1: The rated DC current of the multi-terminal hybrid DC transmission system and the measured DC current of the multi-terminal hybrid DC transmission system satisfy the following formula (4):

[0107]

[0108] Among them, I dcref I represents the rated DC current for a multi-terminal hybrid DC transmission system. dc The measured DC current value for a multi-terminal hybrid DC transmission system;

[0109] Step 2: Based on the droop control characteristics, control the DC voltage compensation amount to be equal to a preset value. The preset value here can be 0.

[0110] The above formula (4) can avoid frequent shifts in the droop characteristic line. The adaptive droop control strategies corresponding to formulas (3) and (4) are as follows: Figure 5 As shown. Where K p and K i For the PI parameters of the outer loop control; i dlim i is the active current limiting value. dref The output DC current rating (active current reference value) is determined by adding a DC voltage compensation amount m to the basic droop control, where m is based on the system's DC voltage rating I. dc Adjustments are made based on changes in the DC current; the droop characteristic line can track the DC current value and shift accordingly, achieving automatic adjustment. To avoid frequent shifts in the droop characteristic line, when... When this occurs, the control strategy is locked, making m = 0. DBLK is the unlock signal; the adaptive droop control is activated when any MMC converter is unlocked. Simultaneously, the rate limiter will limit the compensation rate.

[0111] In one embodiment, step S24, which uses the DC voltage compensation amount of any MMC converter to compensate for the cumulative total output power variation of each MMC converter based on the droop control characteristics, further includes:

[0112] Step 1: If the DC voltage compensation of any MMC converter equals a preset value, keep the droop characteristic line stationary. The preset value here can be 0, for example: when the rated DC voltage I... dc Equal to the rated value of DC current I dcref At this time, the drooping characteristic line does not move, that is, it remains stationary, i.e., m = 0.

[0113] Step 2: If the DC voltage compensation of any MMC converter exceeds a preset value, control the droop characteristic line to move in the first direction. This first direction can be upward. When the system DC current decreases, m > 0, and the droop characteristic line shifts upward, as shown below. Figure 6A As shown.

[0114] Step 3: If the DC voltage compensation of any MMC converter is less than the preset value, control the droop characteristic line to move in the second direction. This second direction can be downwards. When the system DC current increases, m < 0, and the droop characteristic line moves downwards, as shown below. Figure 6B As shown.

[0115] The steps from step one to step three above are not in any particular order. For example, taking a total number of MMC converters n=3 as an example, in... Figure 6A In the process, when the system DC current decreases, m>0, and the droop characteristic automatically shifts upward (equivalent to reducing the active power reference value of the MMC converter), while ensuring that the DC measurement voltage of the MMC converter remains the DC reference voltage (DC voltage rating) U. dcref Under the premise of [reason], the active power output of the MMC converter is reduced. Similarly, under [reason], Figure 6B In this process, when the system DC current increases, m < 0. At this time, the droop characteristic automatically shifts downward (equivalent to increasing the active power reference value of the MMC), thereby increasing the active power output of the MMC converter. Simultaneously, the DC voltage is maintained at the reference voltage (DC voltage rated value) U. dcref .

[0116] In one implementation, the droop control characteristic satisfies the following formula (5):

[0117] P mj -P refj +K drop_j (U dcref -U dc (5) = 0;

[0118] Among them, P mjLet P be the current output power of the j-th MMC converter. refj K represents the rated output power of the j-th MMC converter. drop_j U is the droop characteristic coefficient of the j-th MMC converter. dcref U is the DC voltage rating of any MMC converter. dc This is the measured DC voltage value for any MMC converter. Formula (5) can be obtained through... Figure 6A Or it can be deduced from 6B.

[0119] In one implementation, the DC voltage measurement of any MMC converter is kept stable by the following formula (6):

[0120]

[0121] Among them, U dc P represents the measured DC voltage value of any MMC converter. mj Let P be the current output power of the j-th MMC converter. refj K represents the rated output power of the j-th MMC converter. drop_j U is the droop characteristic coefficient of the j-th MMC converter. dcref Let m be the DC voltage rating of any MMC converter. j DC voltage compensation for the j-th MMC converter.

[0122] In one implementation, the DC voltage measurement of any MMC converter is kept stable in the following manner:

[0123] Step 1: Obtain the droop characteristic line of the multi-terminal hybrid DC transmission system as a result of changes in total output power.

[0124] For example: in Figure 6A and 6B In China, multi-terminal hybrid DC transmission systems shift upwards or downwards due to changes in total output power.

[0125] Step 2: Determine the coordinates (P) of any point on the droop characteristic line that ensures the stability of the DC voltage measurement value for any MMC converter. mj U dcref ).

[0126] For example: in Figure 6A Alternatively, in the sag characteristic line of 6B, select any point coordinate value (P). mj U dcref That is, the rated DC voltage corresponding to the current output power of the j-th MMC converter is U. dcrefCompensating for the DC voltage rating (DC voltage reference value) of any MMC converter is equivalent to compensating for the active power reference value (rated output power of any MMC converter).

[0127] The adaptive droop control method for multi-terminal hybrid DC transmission systems in this embodiment of the invention, through steps S21-S24, introduces a DC voltage compensation amount. On the one hand, it can adaptively adjust the droop characteristics of any MMC converter in real time based on changes in the system's DC current measurement value, thereby avoiding deviations in DC voltage caused by changes in DC current, maintaining the DC voltage at the rated reference value, improving the stability of the system voltage, and ultimately achieving precise control of the DC voltage measurement value of any MMC converter. Simultaneously, it can effectively reduce fluctuations in the DC voltage measurement value of any MMC converter during fault periods. On the other hand, any MMC converter using droop control has the ability to control both DC voltage and DC power, preventing power backfeeding.

[0128] Example 3

[0129] This invention provides an adaptive droop control method for multi-terminal hybrid DC transmission systems, applicable to, for example... Figure 1 The multi-terminal hybrid DC transmission system shown is based on Figure 1 The multi-terminal hybrid DC transmission system shown is used for verification. The overall rated DC voltage of the system is 800kV, and the overall rated output power is 4000MW. Specifically, the rated DC voltage of the high-end LCC converter on the inverter station side is 400kV, with a rated output power of 2000MW. The rated DC voltage of any single low-end MMC converter is 400kV, with a rated output power of 667MW. All MMC converters use droop control and have identical parameters. The rated DC voltage is set to 400kV, and considering losses, the reference value for output active power is set to 650MW.

[0130] The first verification example uses the change of the DC current command value of the LCC rectifier station, i.e., 5kA. The DC current of the system is given. At 3s, 4s, 5s, 6s, and 7s, the DC current command value of the LCC is changed sequentially to 0.9pu, 0.8pu, 0.7pu, 0.6pu, and 0.5pu, as shown in the figure. Figure 7A As shown, the system DC current at various times is represented. Simulations were performed for both cases with and without adaptive droop control, and the simulation results are as follows. Figures 7B-7C As shown. Without adaptive droop control, the DC voltage of the MMC converter decreases as the system DC current decreases, and cannot maintain its rated value; after adopting the proposed adaptive droop control, the DC voltage compensation amount m is based on the system DC current I.dc The DC voltage is adjusted in real time according to the changes, and the drooping characteristic of the MMC is automatically shifted to keep the DC voltage at the rated value.

[0131] The second verification example uses a ground fault as an example. Under master-slave control mode, a single-phase transient ground fault is set at the receiving end of the LCC converter after 3 seconds. The simulation results are as follows: Figures 8A-8B As shown. Since MMC1, which adopts constant DC voltage control, does not have the ability to control DC power, the magnitude of its DC current is determined by the total system current and the DC current of MMC2 and MMC3, which are controlled by constant power. Therefore, when a fault occurs, MMC1 will exhibit power backfeeding, switching from inverter to rectification state, which is not conducive to the stability of the receiving end system.

[0132] With the MMC converter employing droop control, a single-phase transient ground fault is introduced at the receiving end of the LCC converter at 3 seconds. Simulations are performed under both adaptive droop control and no adaptive droop control. The simulation comparison results are as follows: Figures 9A-9B As shown in the figure, since the active power output of each MMC converter is the same under droop control, only the active power waveform of a single MMC is given in the simulation diagram. Compared with master-slave control, during a fault, the MMC converter using droop control has the ability to control both DC voltage and DC power simultaneously, and there will be no power backfeeding problem. Due to the commutation failure of LCC, the system DC current will fluctuate significantly. Without a control strategy, the fluctuation of MMC DC voltage is large, but after adopting the proposed adaptive droop control strategy, the fluctuation of MMC DC voltage is significantly reduced.

[0133] Example 4

[0134] This invention provides an adaptive droop control device for a multi-terminal hybrid DC transmission system, applied to... Figure 1 The multi-terminal hybrid DC transmission system shown in the figure, the device as Figure 10 As shown, it includes the following modules:

[0135] The total power change determination module 101 is used to determine the cumulative total output power change of each MMC converter in the multi-terminal hybrid DC transmission system.

[0136] The parameter acquisition module 102 is used to acquire the rated DC current, measured DC current, droop characteristic coefficient and rated DC voltage of any MMC converter in the multi-terminal hybrid DC transmission system.

[0137] The DC voltage compensation calculation module 103 is used to calculate the DC voltage compensation of any MMC converter based on the rated DC current, measured DC current, droop characteristic coefficient and rated DC voltage of any MMC converter in the multi-terminal hybrid DC transmission system.

[0138] The compensation module 104 is used to compensate for the cumulative total output power variation of each MMC converter based on the droop control characteristics by utilizing the DC voltage compensation amount of any MMC converter.

[0139] In one embodiment, the DC voltage compensation calculation module 103 calculates the DC voltage compensation of any MMC converter based on the rated DC current of the multi-terminal hybrid DC transmission system, the measured DC current, the droop characteristic coefficient of any MMC converter, and the rated DC voltage, using the above formula (3):

[0140] In one embodiment, the compensation module 104 includes:

[0141] A DC current control submodule, and the DC current control submodule satisfies the above formula (4);

[0142] The DC voltage control submodule is used to control the DC voltage compensation amount to equal a preset value based on the droop control characteristics.

[0143] In one embodiment, the compensation module 104 further includes:

[0144] The first droop characteristic determination submodule is used to control the droop characteristic line to remain stationary if the DC voltage compensation of any MMC converter is equal to a preset value.

[0145] The second droop characteristic determination submodule is used to control the droop characteristic line to move in the first direction if the DC voltage compensation of any MMC converter is greater than a preset value.

[0146] The third droop characteristic determination submodule is used to control the droop characteristic line to move in the second direction if the DC voltage compensation of any MMC converter is less than a preset value.

[0147] In one implementation, the droop control characteristics satisfy the above formula (5).

[0148] In one implementation, the DC voltage measurement of any MMC converter is kept stable by the above formula (6):

[0149] In one implementation, the DC voltage measurement of any MMC converter is kept stable by the following module:

[0150] The droop characteristic line acquisition module is used to acquire the droop characteristic line of a multi-terminal hybrid DC transmission system as it shifts due to changes in total output power.

[0151] The coordinate point determination module is used to determine the coordinate value (P) of any point on the drooping characteristic line that ensures the stability of the DC voltage measurement value of any MMC converter. mj U dcref ).

[0152] In one embodiment, the total power change determination module 101 includes:

[0153] The power acquisition submodule is used to acquire the current output power and rated output power of any MMC converter.

[0154] The power deviation calculation submodule is used to calculate the difference between the current output power and the rated output power of any MMC converter to obtain the output power deviation of any MMC converter.

[0155] The power calculation submodule calculates the cumulative total output power change of each MMC converter based on the output power deviation of any MMC converter.

[0156] The adaptive droop control device for the multi-terminal hybrid DC transmission system in this embodiment of the invention introduces a DC voltage compensation amount, so that the droop characteristics of the MMC converter can be adaptively adjusted in real time according to the changes in the system DC current, avoiding deviation of DC voltage with changes in DC current, and maintaining the DC voltage at the rated reference value.

[0157] Example 5

[0158] This invention also provides an electronic device, such as... Figure 11 As shown, the electronic device may include a processor 111, a memory 112, and a multi-terminal hybrid DC transmission system 113, wherein the processor 111, the memory 112, and the multi-terminal hybrid DC transmission system 113 can be connected via a bus or other means. Figure 11 Taking the example of a connection between China and Israel via a bus.

[0159] Processor 111 can be a central processing unit (CPU). Processor 111 can also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or combinations of the above types of chips.

[0160] The memory 112, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs, non-transitory computer-executable programs, and modules. The processor 111 executes various functional applications and data processing by running the non-transitory software programs, instructions, and modules stored in the memory 112, thereby implementing the adaptive droop control method in the above method embodiments.

[0161] The memory 112 may include a program storage area and a data storage area. The program storage area may store the operating system and applications required for at least one function; the data storage area may store data created by the processor 111, etc. Furthermore, the memory 112 may include high-speed random access memory and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some embodiments, the memory 112 may optionally include memory remotely located relative to the processor 111, and these remote memories may be connected to the processor 111 via a network. Examples of such networks include, but are not limited to, power grids, the Internet, enterprise intranets, local area networks, mobile communication networks, and combinations thereof.

[0162] The one or more modules are stored in the memory 112, and when executed by the processor 111, they execute the adaptive droop control method shown in the embodiment of the accompanying drawings.

[0163] The specific details of the above-mentioned electronic device can be understood by referring to the relevant descriptions and effects in the embodiments shown in the accompanying drawings, and will not be repeated here.

[0164] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. The storage medium can be a magnetic disk, optical disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk drive (HDD), or solid-state drive (SSD), etc.; the storage medium can also include combinations of the above types of memory.

[0165] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An adaptive droop control method for a multi-terminal hybrid DC transmission system, characterized in that, Includes the following steps: Determine the cumulative total output power variation of each MMC converter in a multi-terminal hybrid DC transmission system; Obtain the rated DC current, measured DC current, droop characteristic coefficient, and rated DC voltage of any MMC converter in a multi-terminal hybrid DC transmission system; Based on the rated DC current and measured DC current of the multi-terminal hybrid DC transmission system Given the droop characteristic coefficient and DC voltage rating of any MMC converter, calculate the DC voltage compensation for any MMC converter. Using the DC voltage compensation amount of any of the MMC converters, the cumulative total output power variation of each MMC converter is compensated based on the droop control characteristics; Based on the rated DC current, measured DC current, droop characteristic coefficient, and rated DC voltage of the multi-terminal hybrid DC transmission system, the DC voltage compensation of any MMC converter is calculated using the following formula: ； in, This represents the DC voltage compensation amount for the j-th MMC converter. The rated value of the DC current. This is a DC voltage measurement value. This refers to the DC voltage rating of any MMC converter. For the first The droop characteristic coefficient of each MMC converter, where n is the total number of MMC converters; The DC voltage measurement value of any MMC converter is kept stable by the following formula: ； in, This refers to the measured DC voltage value of any MMC converter. For the first The current output power of each MMC converter For the first The rated output power of each MMC converter For the first The droop characteristic coefficient of an MMC converter This refers to the DC voltage rating of any MMC converter. DC voltage compensation for the j-th MMC converter.

2. The adaptive droop control method according to claim 1, characterized in that, Using the DC voltage compensation of any of the MMC converters, the compensation for the cumulative total output power variation of each MMC converter based on the droop control characteristics includes: The rated DC current of the multi-terminal hybrid DC transmission system and the measured DC current of the multi-terminal hybrid DC transmission system satisfy the formula: ； in, The rated DC current of the multi-terminal hybrid DC transmission system is given. The measured value of the DC current in the multi-terminal hybrid DC transmission system; Based on the droop control characteristics, the DC voltage compensation amount is controlled to be equal to a preset value.

3. The adaptive droop control method according to any one of claims 1 to 2, characterized in that, Using the DC voltage compensation of any of the MMC converters, the compensation for the cumulative total output power variation of each MMC converter based on the droop control characteristics also includes: If the DC voltage compensation of any MMC converter is equal to a preset value, the droop characteristic line is kept stationary. If the DC voltage compensation of any MMC converter is greater than the preset value, the droop characteristic line is controlled to move in the first direction. If the DC voltage compensation of any of the MMC converters is less than a preset value, the droop characteristic line is controlled to move in the second direction.

4. The adaptive droop control method according to any one of claims 1 to 2, characterized in that, The droop control characteristic satisfies the formula: - + ( - )=0； in, For the first The current output power of each MMC converter For the first The rated output power of each MMC converter For the first The droop characteristic coefficient of an MMC converter This refers to the DC voltage rating of any MMC converter. This represents the measured DC voltage value for any MMC converter.

5. The adaptive droop control method according to claim 1, characterized in that, The DC voltage measurement value of any MMC converter is kept stable by the following method: Obtain the droop characteristic line of the multi-terminal hybrid DC transmission system as a result of the change in total output power; Determine the coordinates of any point from the drooping characteristic line that ensures the stability of the DC voltage measurement value of any MMC converter. , ).

6. The adaptive droop control method according to claim 1, characterized in that, The cumulative total output power variation of each MMC converter in a multi-terminal hybrid converter DC transmission system includes: Obtain the current output power and rated output power of any MMC converter; The output power deviation of any MMC converter is obtained by calculating the difference between its current output power and rated output power. Based on the output power deviation of any MMC converter, calculate the cumulative total output power change of each MMC converter.

7. An adaptive droop control device for a multi-terminal hybrid DC transmission system, characterized in that, Includes the following modules: The total power change determination module is used to determine the cumulative total output power change of each MMC converter in a multi-terminal hybrid DC transmission system. The parameter acquisition module is used to acquire the rated DC current, measured DC current, droop characteristic coefficient of any MMC converter, and rated DC voltage of the multi-terminal hybrid DC transmission system. The DC voltage compensation calculation module is used to calculate the DC voltage compensation of any MMC converter based on the rated DC current, measured DC current, droop characteristic coefficient and rated DC voltage of the multi-terminal hybrid DC transmission system. The compensation module is used to compensate for the cumulative total output power variation of each MMC converter based on the droop control characteristics by utilizing the DC voltage compensation amount of any MMC converter. Based on the rated DC current, measured DC current, droop characteristic coefficient, and rated DC voltage of the multi-terminal hybrid DC transmission system, the DC voltage compensation of any MMC converter is calculated using the following formula: ； in, This represents the DC voltage compensation amount for the j-th MMC converter. The rated value of the DC current. This is a DC voltage measurement value. This refers to the DC voltage rating of any MMC converter. For the first The droop characteristic coefficient of each MMC converter, where n is the total number of MMC converters; The DC voltage measurement value of any MMC converter is kept stable by the following formula: ； in, This refers to the measured DC voltage value of any MMC converter. For the first The current output power of each MMC converter For the first The rated output power of each MMC converter For the first The droop characteristic coefficient of an MMC converter This refers to the DC voltage rating of any MMC converter. DC voltage compensation for the j-th MMC converter.

8. A multi-terminal hybrid DC transmission system, used in the adaptive droop control method according to any one of claims 1 to 7, characterized in that, include: Sending end AC power grid; The rectifier station includes multiple sets of LCC converters, each set of LCC converters being connected to the sending-end AC power grid. An inverter station includes at least one set of LCC converters and multiple parallel MMC converters. The input terminals of the at least one set of LCC converters are connected to the rectifier station, and the output terminals of the at least one set of LCC converters are connected to the multiple parallel MMC converters. A DC filter is connected to both the rectifier station and the inverter station. The receiving-end AC grid includes multiple AC ports distributed in parallel, each AC port being connected to its corresponding MMC converter.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions for causing the computer to perform the adaptive droop control method according to any one of claims 1 to 7.

10. An electronic device, characterized in that, include: The multi-terminal hybrid DC transmission system, memory, and processor of claim 8 are interconnected, wherein the multi-terminal hybrid DC transmission system, the memory, and the processor are mutually communicatively connected, the memory stores computer instructions, and the processor executes the adaptive droop control method of any one of claims 1 to 7 by executing the computer instructions.

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