Inter-electrode cooperative control method, system, device and medium for improving transient modulation ratio

Abstract

This invention discloses an inter-electrode coordinated control method, system, device, and medium for improving the transient modulation ratio. The method includes: when an AC fault occurs at the sending end of a hybrid transmission system, and the receiving-end converter switches to buck operation with freewheeling, the receiving-end converter compares the magnitude of the DC voltage drop with the steady-state modulation ratio in real time. If the DC voltage drop is greater than or equal to the steady-state modulation ratio, the converter output AC voltage can still maintain good power quality, and the receiving-end converter only needs to engage the basic steady-state control mode, with the reactive power control mode remaining consistent with the steady-state mode. Conversely, in addition to engaging the basic steady-state control mode, the receiving-end converter adds an inter-electrode coordinated control mode to the reactive power control mode to improve the transient modulation ratio. This includes: dynamically adjusting the reactive power and AC voltage reference values ​​during the transient period based on the degree of AC voltage drop at the sending end. This avoids over-modulation of the output AC voltage during buck operation and maintains stable changes in the AC bus voltage.

Description

Technical Field

[0001] This invention relates to the field of DC power transmission technology, and in particular to methods, systems, devices and media for inter-electrode coordinated control to improve transient modulation ratio. Background Technology

[0002] The LCC-MMC hybrid multi-terminal hybrid transmission system, which uses a line commutated converter (LCC) as the centralized power transmission end and multiple modular multilevel converters (MMC) as the multi-point power receiving end, fully utilizes the economic and technical advantages of both types of converters. It provides a new approach for DC power supply in large cities and DC multi-point power receiving in load centers, and also provides a new method for large-scale grid access and transmission and consumption of renewable energy.

[0003] LCC-MMC hybrid DC transmission technology represents a significant future development direction for DC transmission technology and has already been implemented in specific engineering projects in China. However, in large-scale, long-distance power transmission applications, when an AC fault occurs at the sending end of an LCC-MMC hybrid DC system, the differences in the external characteristics and control methods of the LCC and MMC converters can easily lead to a reduction or even interruption in power transmission. To ensure power continuity under these conditions, the receiving-end MMC needs to switch from full-voltage operation to step-down operation. Most existing transmission lines are true bipolar connected, and MMCs often use half-bridge sub-modules. During step-down operation, the MMC may experience power quality degradation due to failure to meet modulation ratio constraints and AC output voltage requirements. This is particularly detrimental to AC systems with high performance requirements connected to the AC output of the LCC-MMC converter station. Summary of the Invention

[0004] Therefore, it is necessary to design inter-electrode coordinated control methods, systems, devices, and media to improve the transient modulation ratio, in order to solve the problem of power quality degradation due to failure to meet modulation ratio constraints and AC output voltage during step-down operation of MMC.

[0005] An inter-pole coordinated control method for improving transient modulation ratio is applied to a hybrid power transmission system, the hybrid power transmission system including a sending-end converter and a receiving-end converter, the method comprising:

[0006] When the sending-end converter experiences an AC fault, the receiving-end converter receives and executes a DC step-down command in real time according to the degree of drop in the AC voltage of the sending-end converter.

[0007] The receiving-end converter compares the magnitude of the DC voltage reduction with the steady-state modulation ratio in real time; wherein, the magnitude of the DC voltage reduction is the ratio of the voltage drop indicated by the DC buck command to the rated value of the steady-state output DC voltage of the receiving-end converter;

[0008] If the DC voltage reduction is greater than or equal to the steady-state modulation ratio, the receiving-end converter only needs to be put into steady-state basic control mode, and the reactive power control mode is consistent with the steady-state mode; wherein, in the steady-state basic control mode, the reference value of DC voltage is the reduced voltage indicated by the DC buck command, and in the reactive power control mode, the reference value of reactive power or the reference value of AC voltage remains unchanged.

[0009] If the DC voltage reduction is less than the steady-state modulation ratio, the receiving-end converter, in addition to the basic steady-state control mode, employs an inter-electrode coordinated control mode to improve the transient modulation ratio. In this inter-electrode coordinated control mode, the reference values ​​of reactive power and AC voltage during the transient period are dynamically adjusted based on the degree of AC voltage drop of the sending-end converter.

[0010] In one embodiment, the reactive power control method is supplemented by an inter-pole coordinated control method to improve the transient modulation ratio, including:

[0011] A dynamic adjustment strategy for positive reactive power and a dynamic adjustment strategy for negative constant AC voltage reference value are implemented. The positive reactive power dynamic adjustment strategy dynamically adjusts the reference value of reactive power during transient periods based on the degree of AC voltage drop of the sending-end converter, and the negative constant AC voltage reference value dynamic adjustment strategy dynamically adjusts the reference value of AC voltage during transient periods.

[0012] In one embodiment, the dynamic adjustment strategy for the input positive reactive power includes:

[0013] Calculate the deviation between the reference value of the virtual equipotential point line voltage of the receiving-end converter and the measured value of the virtual equipotential point line voltage, and use the deviation as the input of the proportional-integral controller to obtain the output value;

[0014] Substitute the effective value of the line voltage of the AC system connected to the receiving-end converter and the reference value of the line voltage at the virtual equipotential point into the reactive power calculation formula, and use the calculation result as the feedforward term.

[0015] The sum of the output value and the feedforward term is used as the reactive power adjustment reference value, and the actual value of the reactive power controlled by the receiving-end converter follows the reactive power adjustment reference value.

[0016] In one embodiment, the method further includes:

[0017] Calculate the ratio of the DC voltage reduction amplitude of the receiving-end converter to the steady-state modulation ratio, and use the product of the calculated ratio and the rated value of the steady-state virtual equipotential point line voltage as the reference value of the virtual equipotential point line voltage.

[0018] In one embodiment, the dynamic adjustment strategy for the negative electrode constant AC voltage reference value includes:

[0019] The reference value of the negative pole constant AC voltage is calculated based on the steady-state AC bus voltage reference value and the effective value of the AC system line voltage. The receiving-end converter controls the AC voltage to follow the negative pole constant AC voltage reference value.

[0020] In one embodiment, the receiving-end converter only needs to be put into steady-state basic control mode, including:

[0021] The actual value of the DC voltage controlled by the receiving-end converter follows the reference value set for buck operation.

[0022] In one embodiment, the reactive power control method remains consistent with the steady state, including:

[0023] The receiving-end positive and negative converters are controlled in either a constant reactive power control mode or a constant AC voltage control mode; wherein, the constant reactive power control mode indicates that the actual value of the reactive power controlled by the receiving-end converter follows the reactive power control reference value set in steady state, and the constant AC voltage control mode indicates that the AC voltage controlled by the receiving-end converter follows the AC bus voltage reference value set in steady state.

[0024] A hybrid power transmission system, the hybrid power transmission system comprising a sending-end converter and a receiving-end converter;

[0025] When an AC fault occurs in the sending-end converter, the sending-end converter sends a DC step-down command according to the degree of AC voltage drop.

[0026] The receiving-end converter is used to receive and execute DC buck commands in real time, and to compare the magnitude of the DC voltage reduction with the steady-state modulation ratio in real time; wherein, the DC voltage reduction is the ratio of the voltage drop indicated by the DC buck command to the rated value of the steady-state output DC voltage of the receiving-end converter.

[0027] If the DC voltage reduction is greater than or equal to the steady-state modulation ratio, then only the steady-state basic control mode needs to be activated, and the reactive power control mode remains consistent with the steady-state mode; wherein, in the steady-state basic control mode, the reference value of the DC voltage is the reduced voltage indicated by the DC voltage reduction command, and in the reactive power control mode, the reference value of the reactive power or the reference value of the AC voltage remains unchanged.

[0028] If the DC voltage reduction is less than the steady-state modulation ratio, then in addition to the steady-state basic control mode, an inter-electrode coordinated control mode to improve the transient modulation ratio is added to the reactive power control mode; wherein, in the inter-electrode coordinated control mode to improve the transient modulation ratio, the reference values ​​of reactive power and AC voltage during the transient period are dynamically adjusted according to the degree of drop in AC voltage of the sending-end converter.

[0029] A computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform the steps of the above-described method for improving the inter-pole cooperative control of transient modulation ratio.

[0030] An inter-electrode cooperative control device for improving transient modulation ratio includes a memory and a processor. The memory stores a computer program, which, when executed by the processor, causes the processor to perform the steps of the aforementioned inter-electrode cooperative control method for improving transient modulation ratio.

[0031] This invention provides an inter-electrode coordinated control method, system, device, and medium for improving the transient modulation ratio. When an AC fault occurs in the sending-end converter, the receiving-end converter receives and executes a DC voltage reduction command in real time based on the degree of AC voltage drop in the sending-end converter. Considering the maximum constraint on the modulation ratio of the receiving-end converter, when the AC fault is severe, the required voltage reduction value of the receiving-end converter is large. The receiving-end converter compares the DC voltage reduction magnitude with the steady-state modulation ratio in real time. If the DC voltage reduction magnitude is greater than or equal to the steady-state modulation ratio, it indicates that good power quality can still be maintained. In this case, the receiving-end converter only needs to engage the steady-state basic control mode, and the reactive power control mode remains consistent with the steady-state mode. If the DC voltage reduction is less than the steady-state modulation ratio, additional adjustments are needed to maintain good power quality. In this case, the receiving-end converter, in addition to the basic steady-state control mode, employs a reactive power control mode supplemented by an inter-electrode coordinated control mode to increase the transient modulation ratio. This inter-electrode coordinated control mode dynamically adjusts the reference values ​​of reactive power and AC voltage during the transient period based on the degree of AC voltage drop at the sending-end converter. By controlling the receiving-end converter to dynamically adjust reactive power, the amplitude of its output AC voltage can be reduced, thus avoiding over-modulation of the output AC voltage during buck operation. Furthermore, during rapid reactive power regulation, controlling the receiving-end converter to dynamically adjust AC voltage maintains stable changes in the AC bus voltage. This solves the problem of power quality degradation due to failure to meet modulation ratio constraints and AC output voltage, making it suitable for applications with high requirements for the AC output characteristics of converter stations. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0033] in:

[0034] Figure 1 This is a flowchart illustrating an inter-pole cooperative control method for improving transient modulation ratio in one embodiment.

[0035] Figure 2 This is a topology diagram of a hybrid power transmission system in one embodiment;

[0036] Figure 3 A schematic diagram of a dynamic adjustment strategy for positive reactive power input;

[0037] Figure 4 A schematic diagram of a strategy for dynamically adjusting the AC voltage reference value for the negative terminal.

[0038] Figure 5 This is the equivalent circuit diagram of a single-pole MMC.

[0039] Figure 6 This is a schematic diagram of a hybrid power transmission system in one embodiment;

[0040] Figure 7 This is a block diagram of an inter-pole coordinated control device for improving transient modulation ratio in one embodiment. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] like Figure 1 As shown, Figure 1 This is a flowchart illustrating an inter-pole coordinated control method for improving the transient modulation ratio in one embodiment, applied to a hybrid transmission system including a sending-end converter and a receiving-end converter. Figure 2 The diagram shown is a topology diagram of a hybrid power transmission system in one embodiment, including: a sending-end converter LLC, which serves as a rectifier station and is used to convert AC power into DC power for transmission; and a receiving-end converter MMC, which serves as an inverter station and is used to convert DC power into AC power.

[0043] The steps provided by the inter-pole cooperative control method for improving the transient modulation ratio in this embodiment include:

[0044] Step 102: When an AC fault occurs in the sending-end converter, the receiving-end converter receives and executes a DC step-down command in real time according to the degree of drop in the AC voltage of the sending-end converter.

[0045] When the LLC experiences AC faults of varying severity, the MMC receives and executes different DC buck commands, each indicating a voltage drop to ensure power continuity under that operating condition. The generation method of these DC buck commands is existing technology. This invention sets the MMC to receive a DC buck command U in real time under fault conditions. dc_ref .

[0046] Step 104: The receiving-end converter compares the magnitude of the DC voltage reduction with the steady-state modulation ratio in real time. If the magnitude of the DC voltage reduction is greater than or equal to the steady-state modulation ratio, proceed to step 106; if the magnitude of the DC voltage reduction is less than the steady-state modulation ratio, proceed to step 108.

[0047] First, it's worth noting that the DC voltage reduction is the same as the voltage drop U indicated by the DC buck command. dc_ref With MMC steady-state output DC voltage rating U dcN The ratio is expressed as:

[0048]

[0049] The modulation ratio m in MMC refers to:

[0050]

[0051] Among them, v m U represents the peak-to-average value of the three-phase output voltage on the AC side of the MMC. dc This refers to the DC voltage on the DC side of the MMC. The steady-state modulation ratio M is typically around 0.875.

[0052] It is known that the modulation ratio of a half-bridge MMC is always less than or equal to 1 (i.e., modulation ratio constraint). When the modulation ratio is greater than 1, the AC voltage output by the MMC is not a standard sine wave (waveform clipping), resulting in increased harmonic distortion. Therefore, during buck operation, the denominator in the above formula for the modulation ratio m is reduced, so the modulation ratio increases. When the modulation ratio is greater than 1, the power quality of the AC voltage will deteriorate.

[0053] Therefore, based on the modulation ratio (m) constraint, the half-bridge MMC should ideally satisfy m ≤ 1 at all times during operation, while the steady-state modulation ratio M in this step is generally taken as around 0.875. When the required voltage drop of the MMC is relatively small (corresponding U... dc_ref With steady-state value UdcN (Small deviation), i.e., the downward adjustment range When the steady-state modulation ratio M is greater than or equal to the value of M, during buck operation, by executing step 106, the MMC can maintain good power quality of the AC side output voltage simply by increasing the modulation ratio m to the maximum value of 1.

[0054] However, when m increases to the critical value of its maximum value of 1, that is... Initially, the modulation ratio is less than the steady-state modulation ratio M. At this point, it is desirable to maintain the modulation ratio at 1. By executing step 108, the denominator of the above transient modulation ratio formula is dynamically reduced so that m equals 1.

[0055] Therefore, this step can be understood as determining the relationship between μ and the steady-state modulation ratio M, that is, determining the actual process of the modulation ratio continuously increasing to 1 and then remaining at 1.

[0056] Step 106: The receiving-end converter only needs to be put into steady-state basic control mode, and the reactive power control mode should be consistent with the steady-state mode.

[0057] In the steady-state basic control mode, the reference value of DC voltage is the reduced voltage indicated by the DC step-down command to achieve step-down follow current. In the reactive power control mode, the reference value of reactive power or the reference value of AC voltage remains unchanged.

[0058] In one specific embodiment, the MMC (Medium-terminal Controller) engages a steady-state basic control mode, including: the MMC controls the actual value of the DC voltage to follow the reference value set for buck operation, i.e., constant DC voltage control, thereby maintaining the DC voltage stability of the transmission system. Correspondingly, the LCC (Limited-current Controller) also controls the actual value of the DC current to follow the reference value set for buck operation, i.e., constant DC current control, thereby maintaining the power stability of the transmission system. Here, "following" in this embodiment means ensuring that the actual value eventually equals the reference value, or that the actual value deviates very little from the reference value.

[0059] The MMC uses a true bipolar connection. In one specific embodiment, the reactive power control method remains consistent with the steady-state control, including: a control method for constant reactive power input to the positive terminal of the MMC. For details, see [link to documentation]. Figure 3 , Figure 3 This is a schematic diagram illustrating the dynamic adjustment strategy for positive reactive power. The constant reactive power control mode indicates that the actual reactive power value controlled by the MMC follows the reactive power control reference value Q set in steady state. refN That is to say Figure 3 The final reference value Q was determined in the middle. ref Input Q refN Let the actual value follow.

[0060] In addition, reactive power control methods that maintain consistency with steady-state control also include: a control method that connects a constant AC voltage to the negative terminal of the MMC, specifically, such as... Figure 4 As shown, the constant AC voltage control mode indicates that the MMC controls the AC voltage to follow the set AC bus voltage reference value U when in steady state. pcc_N That is to say Figure 4 The final reference value U was determined in the middle. acref Investment U pcc_N Let the actual value follow.

[0061] Since the reference values ​​of reactive power and AC voltage remain unchanged in reactive power control methods, the MMC can maintain good power quality of the AC side output voltage simply by increasing the modulation ratio m to the maximum value of 1.

[0062] Step 108: On the basis of the steady-state basic control mode, the receiving-end converter adds an inter-pole coordinated control mode to the reactive power control mode to improve the transient modulation ratio.

[0063] The steady-state basic control method here is the same as that in step 106, so it will not be repeated here. However, in the inter-electrode coordinated control method to improve the transient modulation ratio, the reference values ​​of reactive power and AC voltage during the transient period are dynamically adjusted according to the degree of AC voltage drop at the sending-end converter.

[0064] In one specific embodiment, the inter-pole coordinated control method for improving the transient modulation ratio includes: implementing a dynamic adjustment strategy for positive reactive power and a dynamic adjustment strategy for the negative constant AC voltage reference value. Specifically, the positive reactive power dynamic adjustment strategy dynamically adjusts the reference value of reactive power during the transient period based on the degree of AC voltage drop at the sending-end converter, while the negative constant AC voltage reference value dynamic adjustment strategy dynamically adjusts the reference value of AC voltage during the transient period. In this way, when the actual value follows these dynamically set reference values, the modulation ratio can be maintained at 1, thus widening the voltage drop range of the MMC while maintaining good power quality.

[0065] Specifically, such as Figure 3 As shown, Figure 3 This is a schematic diagram illustrating the dynamic adjustment strategy for positive electrode reactive power. Wherein, U diff_ref The virtual equipotential point line voltage reference value is equivalent to the effective value of the converter output AC line voltage, and the calculation formula is:

[0066]

[0067] In the formula, U diffN This is the rated value of the line voltage at the steady-state virtual equipotential point.

[0068] U′ diffThis represents the measured line voltage at the virtual equipotential point of the converter during step-down operation. Q′ ref This is the reference value for reactive power adjustment required during step-down operation; Q ref This is the reference value for the final input reactive power control;

[0069] The specific dynamic adjustment strategy for positive reactive power is as follows:

[0070] (1) Calculate the reference value U of the virtual equipotential point line voltage of MMC. diff_ref Measured line voltage U′ at the virtual equipotential point diff The deviation between the two values ​​is used as the input to the proportional-integral (PI) controller to obtain the output value.

[0071] (2) Substitute the effective value of the line voltage of the AC system connected to the MMC and the reference value of the line voltage of the virtual equipotential point into the reactive power calculation formula, and use the calculation result as the feedforward term.

[0072] (3) Use the sum of the output value and the feedforward term as the reactive power adjustment reference value Q′. ref The actual value of reactive power controlled by MMC follows the reactive power adjustment reference value Q′. ref That is to say, Figure 3 The final reference value Q was determined in the middle. ref By Q refN Input Q′ ref Let the actual value follow.

[0073] Understandably, the positive terminal of the MMC reduces the amplitude of the AC voltage output by absorbing reactive power from the AC system (i.e., v in m This ensures that the numerator and denominator in the modulation ratio formula decrease simultaneously in a certain proportion (ensuring that m is always less than or equal to 1), thus widening the voltage drop range of the MMC. Furthermore, the amount of reactive power absorbed by the MMC follows the voltage drop U. dc_ref The magnitude of the reactive power is determined by the dynamic adjustment strategy of the positive electrode reactive power in this application. Different voltage drops correspond to different reactive power, thus achieving the effect of stratified quantitative reactive power absorption.

[0074] like Figure 4 As shown, Figure 4 A schematic diagram illustrating the dynamic adjustment strategy for the negative electrode constant AC voltage reference value. Wherein, U pcc_N U is the reference value for steady-state AC bus voltage. s This represents the effective value of the line voltage in the AC system.

[0075] The specific dynamic adjustment strategy for the negative pole constant AC voltage reference value is as follows: based on the steady-state AC bus voltage reference value U... pcc_N The effective value of the line voltage U of the AC system sCalculate the reference value of the negative terminal constant AC voltage. MMC control AC voltage follows the negative electrode and determines the AC voltage reference value U. acref That is to say Figure 4 The final reference value U was determined in the middle. acref byU pcc_N Investment Let the actual value follow.

[0076] For example, based on Figure 5 Explanation U acref The calculation process, in which Figure 5 This is the equivalent circuit diagram of a single-pole MMC. pcc_N instruct Figure 5 At PCC; X s This represents the equivalent reactance between the PCC and the AC system. The calculation process is as follows: Ignoring factors such as bridge arm resistance and active power transmission, based on the magnitude and direction of reactive power exchange at the PCC point, the reactive power absorbed by the unipolar MMC to satisfy the modulation ratio constraint is Q. ref At that time, the effective value of the PCC AC voltage is given by equation (1); similarly, during the MMC buck operation, in order to maintain the transient modulation ratio at its maximum value of 1, the reactive power absorbed is 2Q. ref Therefore, the U at the PCC of the MMC converter station acref As shown in equation (2).

[0077]

[0078]

[0079] Considering that the reactive power absorption period at the positive electrode of the MMC will cause fluctuations in the AC bus voltage of the MMC (reactive power and AC voltage changes are directly related), in this application, the MMC uses the above-mentioned dynamic adjustment strategy of setting the AC voltage reference value at the negative electrode to achieve stable changes in the AC bus during the rapid regulation of reactive power.

[0080] The aforementioned inter-pole coordinated control method for improving the transient modulation ratio involves the receiving-end converter receiving and executing a DC voltage reduction command in real time when an AC fault occurs in the sending-end converter, based on the degree of AC voltage drop in the sending-end converter. Considering the maximum constraint on the modulation ratio of the receiving-end converter, a larger voltage reduction value is required when the AC fault is severe. The receiving-end converter compares the DC voltage reduction magnitude with the steady-state modulation ratio in real time. If the DC voltage reduction magnitude is greater than or equal to the steady-state modulation ratio, it indicates that good power quality can still be maintained. In this case, the receiving-end converter only needs to engage the basic steady-state control mode, and the reactive power control mode remains consistent with the steady-state mode. If the DC voltage reduction is less than the steady-state modulation ratio, additional adjustments are needed to maintain good power quality. In this case, the receiving-end converter, in addition to the basic steady-state control mode, employs a reactive power control mode supplemented by an inter-electrode coordinated control mode to increase the transient modulation ratio. This inter-electrode coordinated control mode dynamically adjusts the reference values ​​of reactive power and AC voltage during the transient period based on the degree of AC voltage drop at the sending-end converter. By controlling the receiving-end converter to dynamically adjust reactive power, the amplitude of its output AC voltage can be reduced, thus avoiding over-modulation of the output AC voltage during buck operation. Furthermore, during rapid reactive power regulation, controlling the receiving-end converter to dynamically adjust AC voltage maintains stable changes in the AC bus voltage. This solves the problem of power quality degradation due to failure to meet modulation ratio constraints and AC output voltage, making it suitable for applications with high requirements for the AC output characteristics of converter stations.

[0081] In one embodiment, such as Figure 6 As shown, a hybrid power transmission system is proposed, which includes a sending-end converter 602 and a receiving-end converter 604:

[0082] When an AC fault occurs in the sending-end converter 602, the sending-end converter 602 sends a DC step-down command according to the degree of AC voltage drop.

[0083] The receiving-end converter 604 is used to receive and execute DC buck commands in real time, and to compare the magnitude of the DC voltage reduction with the steady-state modulation ratio in real time; wherein, the DC voltage reduction is the ratio of the voltage drop indicated by the DC buck command to the rated value of the steady-state output DC voltage of the receiving-end converter 604.

[0084] If the DC voltage reduction is greater than or equal to the steady-state modulation ratio, only the steady-state basic control mode needs to be activated, and the reactive power control mode remains consistent with the steady-state mode. In the steady-state basic control mode, the reference value of the DC voltage is the reduced voltage indicated by the DC voltage reduction command, and the reference value of the reactive power or the reference value of the AC voltage remains unchanged in the reactive power control mode.

[0085] If the DC voltage reduction is less than the steady-state modulation ratio, then on the basis of the steady-state basic control mode, the reactive power control mode is supplemented with an inter-pole coordinated control mode to improve the transient modulation ratio. In the inter-pole coordinated control mode to improve the transient modulation ratio, the reference values ​​of reactive power and AC voltage during the transient period are dynamically adjusted according to the degree of AC voltage drop of the sending-end converter 602.

[0086] Figure 7 An internal structural diagram of an inter-pole cooperative control device for improving transient modulation ratio is shown in one embodiment. Figure 7 As shown, the inter-electrode cooperative control device for improving transient modulation ratio includes a processor, a memory, and a network interface connected via a system bus. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system and may also store a computer program. When executed by the processor, this computer program enables the processor to implement the inter-electrode cooperative control method for improving transient modulation ratio. The internal memory may also store a computer program, which, when executed by the processor, enables the processor to implement the inter-electrode cooperative control method for improving transient modulation ratio. Those skilled in the art will understand that... Figure 7 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the inter-pole cooperative control device for improving transient modulation ratio applied thereto. The specific inter-pole cooperative control device for improving transient modulation ratio may include more or fewer components than shown in the figure, or combine certain components, or have different component arrangements.

[0087] An inter-pole coordinated control device for improving transient modulation ratio includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it performs the following steps: When an AC fault occurs in the sending-end converter, the receiving-end converter receives and executes a DC voltage reduction command in real time according to the degree of AC voltage drop in the sending-end converter; the receiving-end converter compares the magnitude of the DC voltage reduction with the steady-state modulation ratio in real time; if the magnitude of the DC voltage reduction is greater than or equal to the steady-state modulation ratio, the receiving-end converter only needs to engage the basic steady-state control mode, and the reactive power control mode remains consistent with the steady-state mode; if the magnitude of the DC voltage reduction is less than the steady-state modulation ratio, the receiving-end converter, in addition to engaging the basic steady-state control mode, adds an inter-pole coordinated control mode to the reactive power control mode to improve the transient modulation ratio.

[0088] A computer-readable storage medium storing a computer program, which, when executed by a processor, performs the following steps: when an AC fault occurs in the sending-end converter, the receiving-end converter receives and executes a DC voltage reduction command in real time according to the degree of AC voltage drop in the sending-end converter; the receiving-end converter compares the magnitude of the DC voltage reduction with the steady-state modulation ratio in real time; if the magnitude of the DC voltage reduction is greater than or equal to the steady-state modulation ratio, the receiving-end converter only needs to engage the basic steady-state control mode, and the reactive power control mode remains consistent with the steady-state mode; if the magnitude of the DC voltage reduction is less than the steady-state modulation ratio, the receiving-end converter, in addition to engaging the basic steady-state control mode, adds an inter-pole coordinated control mode to the reactive power control mode to increase the transient modulation ratio.

[0089] It should be noted that the above-mentioned inter-electrode cooperative control method, system, device and computer-readable storage medium for improving transient modulation ratio belong to the same general inventive concept, and the contents of the embodiments of the inter-electrode cooperative control method, system, device and computer-readable storage medium for improving transient modulation ratio are applicable to each other.

[0090] 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. This program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and RAMbus dynamic RAM (RDRAM), etc.

[0091] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0092] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for improving the transient modulation ratio through inter-electrode cooperative control, characterized in that, Applied to a hybrid power transmission system, the hybrid power transmission system including a sending-end converter and a receiving-end converter, the method includes: When the sending-end converter experiences an AC fault, the receiving-end converter receives and executes a DC step-down command in real time according to the degree of drop in the AC voltage of the sending-end converter. The receiving-end converter compares the magnitude of the DC voltage reduction with the steady-state modulation ratio in real time; wherein, the magnitude of the DC voltage reduction is the ratio of the voltage drop indicated by the DC buck command to the rated value of the steady-state output DC voltage of the receiving-end converter; If the DC voltage reduction is greater than or equal to the steady-state modulation ratio, the receiving-end converter only needs to be put into steady-state basic control mode, and the reactive power control mode is consistent with the steady-state mode; wherein, in the steady-state basic control mode, the reference value of DC voltage is the reduced voltage indicated by the DC buck command, and in the reactive power control mode, the reference value of reactive power or the reference value of AC voltage remains unchanged. If the DC voltage reduction is less than the steady-state modulation ratio, the receiving-end converter, in addition to the basic steady-state control mode, employs an inter-electrode coordinated control mode to improve the transient modulation ratio. In this inter-electrode coordinated control mode, the reference values ​​of reactive power and AC voltage during the transient period are dynamically adjusted based on the degree of AC voltage drop of the sending-end converter. The receiving-end converter only needs to be put into steady-state basic control mode, including: The actual value of the DC voltage controlled by the receiving-end converter follows the reference value set for buck operation; The reactive power control method is consistent with the steady state, including: The receiving-end converter is configured to operate in either a constant reactive power control mode or a constant AC voltage control mode; wherein, the constant reactive power control mode indicates that the actual value of the reactive power controlled by the receiving-end converter follows the reactive power control reference value set in steady state, and the constant AC voltage control mode indicates that the AC voltage controlled by the receiving-end converter follows the AC bus voltage reference value set in steady state.

2. The method according to claim 1, characterized in that, The reactive power control method is supplemented by an inter-pole coordinated control method to improve the transient modulation ratio, including: A dynamic adjustment strategy for positive reactive power and a dynamic adjustment strategy for negative constant AC voltage reference value are implemented. The positive reactive power dynamic adjustment strategy dynamically adjusts the reference value of reactive power during transient periods based on the degree of AC voltage drop of the sending-end converter, and the negative constant AC voltage reference value dynamic adjustment strategy dynamically adjusts the reference value of AC voltage during transient periods.

3. The method according to claim 2, characterized in that, The dynamic adjustment strategy for the input positive reactive power includes: The deviation between the reference value of the virtual equipotential point line voltage of the receiving-end converter and the measured value of the virtual equipotential point line voltage is calculated, and the deviation is used as the input of the proportional-integral controller to obtain the output value. Substitute the effective value of the line voltage of the AC system connected to the receiving-end converter and the reference value of the line voltage at the virtual equipotential point into the reactive power calculation formula, and use the calculation result as a feedforward term. The sum of the output value and the feedforward term is used as the reactive power adjustment reference value, and the actual value of the reactive power controlled by the receiving-end converter follows the reactive power adjustment reference value.

4. The method according to claim 3, characterized in that, The method further includes: Calculate the ratio of the DC voltage reduction amplitude of the receiving-end converter to the steady-state modulation ratio, and use the product of the calculated ratio and the rated value of the steady-state virtual equipotential point line voltage as the reference value of the virtual equipotential point line voltage.

5. The method according to claim 2, characterized in that, The dynamic adjustment strategy for the reference value of the negative terminal constant AC voltage includes: The reference value of the negative pole constant AC voltage is calculated based on the steady-state AC bus voltage reference value and the effective value of the AC system line voltage. The receiving-end converter controls the AC voltage to follow the negative pole constant AC voltage reference value.

6. A hybrid power transmission system, characterized in that, The hybrid power transmission system includes a sending-end converter and a receiving-end converter; When an AC fault occurs in the sending-end converter, the sending-end converter sends a DC step-down command according to the degree of AC voltage drop. The receiving-end converter is used to receive and execute DC buck commands in real time, and to compare the magnitude of the DC voltage reduction with the steady-state modulation ratio in real time; wherein, the DC voltage reduction is the ratio of the voltage drop indicated by the DC buck command to the rated value of the steady-state output DC voltage of the receiving-end converter. If the DC voltage reduction is greater than or equal to the steady-state modulation ratio, then only the steady-state basic control mode needs to be activated, and the reactive power control mode remains consistent with the steady-state mode; wherein, in the steady-state basic control mode, the reference value of the DC voltage is the reduced voltage indicated by the DC voltage reduction command, and in the reactive power control mode, the reference value of the reactive power or the reference value of the AC voltage remains unchanged. If the DC voltage reduction is less than the steady-state modulation ratio, then on the basis of the steady-state basic control mode, an inter-electrode coordinated control mode to improve the transient modulation ratio is added to the reactive power control mode; wherein, in the inter-electrode coordinated control mode to improve the transient modulation ratio, the reference values ​​of reactive power and AC voltage during the transient period are dynamically adjusted according to the degree of drop of AC voltage of the sending-end converter. The receiving-end converter only needs to be put into steady-state basic control mode, including: The actual value of the DC voltage controlled by the receiving-end converter follows the reference value set for buck operation; The reactive power control method is consistent with the steady state, including: The receiving-end converter is configured to operate in either a constant reactive power control mode or a constant AC voltage control mode; wherein, the constant reactive power control mode indicates that the actual value of the reactive power controlled by the receiving-end converter follows the reactive power control reference value set in steady state, and the constant AC voltage control mode indicates that the AC voltage controlled by the receiving-end converter follows the AC bus voltage reference value set in steady state.

7. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, the processor performs the steps of the method as described in any one of claims 1 to 5.

8. An inter-pole cooperative control device for improving transient modulation ratio, comprising a memory and a processor, characterized in that, The memory stores a computer program that, when executed by the processor, causes the processor to perform the steps of the method as described in any one of claims 1 to 5.

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