Multi-infeed high-voltage direct-current power transmission system based on energy storage and commutation failure self-adaptive suppression method

Abstract

The invention discloses a multi-infeed high-voltage direct-current power transmission system based on energy storage and a commutation failure self-adaptive suppression method. The system comprises a first LCC-HVDC direct-current power transmission system, a second LCC-HVDC direct-current power transmission system, an energy storage system and a transient reactive power control system, the method comprises the following steps: establishing a main circuit model, and designing a control circuit of the MIDC according to the main circuit model and a transient reactive power control system; designing an inverter control circuit of the energy storage system based on the main circuit model and related parameters of the transient reactive power control system; on the basis of each model and each circuit design, comparing a voltage value with a turn-off angle value, triggering a corresponding reactive power reference value generator to output reactive power according to a comparison result and a voltage drop interval, and performing self-adaptive suppression when commutation of the multi-infeed high-voltage direct-current system fails through the reactive power. The reactive power of the system is subjected to adaptive coordination control during commutation failure, the advantage of rapidly providing the reactive power by energy storage is combined, and the commutation failure suppression efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of multi-infeed high-voltage direct current (HVDC) transmission system technology, and in particular to an energy storage-based multi-infeed HVDC transmission system and method. Background Technology

[0002] With the continuous advancement of high-voltage direct current (HVDC) transmission projects, integrating multiple DC lines into a shared AC grid has become increasingly common, resulting in complex mixed-mode DC (MIDC) systems. Compared to single-feeder DC systems, multi-feeder structures further accelerate the coupling between DC lines and the receiving grid, limiting the flexibility of system operation. Simultaneously, the risk of a single fault triggering interlocking faults in the hybrid AC / DC system increases significantly. Therefore, operating conditions become more complex, placing higher demands on system operation and control.

[0003] Commutation failure is one of the common and serious faults in low-voltage direct current (DC) transmission systems, impacting power system operation in multiple ways. Commutation failure typically leads to a decrease in phase-change voltage and an increase in DC current, resulting in a reduction in DC transmission power. Generally, the first commutation failure is unavoidable. However, when the fault is severe, the inverter-side converter station consumes a significant amount of reactive power during the recovery process. If the receiving grid and the reactive power compensation devices on the inverter side cannot provide sufficient reactive power support, the first commutation failure may not be recovered in time, leading to subsequent successive commutation failures. Due to the complex coupling characteristics of AC / DC hybrid systems, multiple consecutive commutation failures can cause drastic fluctuations in DC transmission power, even triggering DC blocking control and causing DC transmission power interruption. In this situation, it not only has a significant impact on the AC grid but may also lead to cascading failures across the region, resulting in widespread power loss. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the aforementioned existing problems, this invention is proposed. Therefore, this invention provides a multi-infeed HVDC transmission system based on energy storage to solve the problem that commutation failure in multi-infeed HVDC transmission systems can easily lead to fluctuations in DC transmission power and even trigger cascading faults.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a multi-infeed high-voltage direct current transmission system based on energy storage, comprising:

[0008] The first LCC-HVDC DC transmission system, the second LCC-HVDC DC transmission system, and the energy storage system;

[0009] The first LCC-HVDC DC transmission system and the second LCC-HVDC DC transmission system are connected via a first tie line, the first LCC-HVDC DC transmission system and the energy storage system are connected via a second tie line, and the second LCC-HVDC DC transmission system and the energy storage system are connected via a third tie line.

[0010] The first LCC-HVDC DC transmission system and the second LCC-HVDC DC transmission system are used for long-distance, low-loss power transmission, and the control circuit ensures the power transmission stability of a single line.

[0011] Energy storage systems are used to provide dynamic reactive power support for multi-infeed HVDC transmission systems and suppress commutation failures.

[0012] As a preferred embodiment of the energy storage-based multi-infeed high-voltage direct current transmission system described in this invention, it further includes a transient reactive power control system.

[0013] The transient reactive power control system includes a fault judgment module, a voltage judgment module, a first reactive power reference value generator, a second reactive power reference value generator, and a third reactive power reference value generator.

[0014] As a preferred embodiment of the energy storage-based multi-infeed high-voltage direct current transmission system described in this invention, the first LCC-HVDC direct current transmission system and the second LCC-HVDC direct current transmission system both include: a synchronous motor, an equivalent impedance, a filter, a transformer, a converter, and corresponding transmission lines and control circuits.

[0015] The converter is controlled by a converter control circuit, which includes a first first-order inertial element, a first inverting adder, a low-voltage current limiting controller, a minimum value selector, a second first-order inertial element, a compensation resistor, a second inverting adder, a third inverting adder, a first PI controller, a current deviation controller, a minimum turn-off angle measurement module, a fourth inverting adder, a second maximum value selection module, a second PI controller, and a second maximum value selector.

[0016] As a preferred embodiment of the multi-infeed high-voltage direct current transmission system based on energy storage described in this invention, the energy storage system includes an energy storage module, a DC-DC converter, a DC-DC converter control circuit, an inverter, an inverter control circuit, an inverter-side equivalent impedance, and an inverter-side synchronous motor.

[0017] The inverter control circuit includes a fifth inverting adder, a third PI controller, a sixth inverting adder, a fourth PI controller, a current inner loop controller, an inverse Park converter, and a PWM modulator.

[0018] As a preferred embodiment of the multi-infeed HVDC transmission system based on energy storage described in this invention, the fault diagnosis module includes:

[0019] The input values ​​of the fault judgment module are AC voltage and turn-off angle. The output signal is sent to the third reactive power reference value generator and the voltage judgment module. The output of the voltage judgment module is sent to the first reactive power reference value generator and the second reactive power reference value generator. The output signals of the first reactive power reference value generator, the second reactive power reference value generator and the third reactive power reference value generator are sent to the negative terminal of the sixth inverting adder.

[0020] Secondly, this invention provides an adaptive suppression method for commutation failure in multi-infeed HVDC transmission systems based on energy storage, comprising:

[0021] Based on the parameters of the first LCC-HVDC DC transmission system and the second LCC-HVDC DC transmission system, a main circuit model of MIDC is established;

[0022] Based on the main circuit model of MIDC and combined with the relevant parameters of the transient reactive power control system, the control circuit of MIDC is designed. When the control circuit of MIDC is running normally, the inverter adopts constant extinction angle control. During the transient process, the inverter side of MIDC uses current deviation control to smoothly switch between constant extinction angle control and constant current control.

[0023] Based on the main circuit parameters of the energy storage system, a main circuit model is established. Based on the main circuit model and the relevant parameters of the transient reactive power control system, the inverter control circuit of the energy storage system is designed.

[0024] Based on various models and circuit designs, the actual voltage value of the multi-infeed HVDC transmission system is compared with the set voltage threshold, and the actual value of the turn-off angle is compared with the set turn-off angle threshold. According to the comparison results and voltage drop range, the corresponding reactive power reference value generator is triggered to output reactive power. The reactive power is used to adaptively suppress the commutation failure of the multi-infeed HVDC system.

[0025] As a preferred embodiment of the adaptive suppression method for commutation failure in a multi-infeed HVDC transmission system based on energy storage described in this invention, the method includes: adaptive suppression of commutation failure in the multi-infeed HVDC system using reactive power, comprising:

[0026] When the voltage is less than or equal to the third voltage and the actual value of the turn-off angle is less than or equal to the set turn-off angle threshold, the reactive power compensation command is divided according to the percentage of voltage drop.

[0027] When the voltage drop is between the first voltage and the second voltage, the first reactive power reference generator is triggered and starts, and the output reactive power is expressed as:

[0028] Q ref =k1×Q set ×(1-U)

[0029] Among them, Q ref The reactive power reference value is the input to the inverter control circuit of the energy storage system; k1 is the first droop coefficient, Q set The initial reactive power reference value input to the inverter control circuit of the energy storage system during transients is set to 1, and U is the voltage value at the grid connection point of the energy storage system.

[0030] When the voltage drop is between the second and third voltages, the second reactive power reference generator is triggered and starts, and the output reactive power is expressed as:

[0031] Q ref =k2×Q set ×U

[0032] Among them, Q ref Q is the reactive power reference value input to the inverter control circuit of the energy storage system; k2 is the second droop coefficient, Q set The initial reactive power reference value input to the inverter control circuit of the energy storage system during transient states is set to 1, and U is the voltage value at the grid connection point of the energy storage system.

[0033] As a preferred embodiment of the adaptive suppression method for commutation failure in a multi-infeed HVDC transmission system based on energy storage described in this invention, the main circuit model includes:

[0034] The converter is modeled using a mean-valued model, equivalent to a boost circuit and a DC parallel capacitor, as follows:

[0035]

[0036] Among them, i L U is the boost inductor current; batt U is the output voltage of the lithium battery array. dc It is the DC voltage of the inverter, i dc It is the DC current of the inverter.

[0037] The grid-connected inverter is modeled using a mean value model, and is represented as follows:

[0038]

[0039] Among them, i gd and i gq Let d and q be the output current of the inverter, and e be the output current of the inverter.d e q The d and q components of the AC voltage on the grid side; u gd and u gq d and q modulation of DC voltage; L is the inductance of the Boost circuit; L r Lr is the inverter-side filter inductance; v i D is the single-phase AC voltage on the inverter side. i is the single-phase modulation ratio; i takes values ​​of abc.

[0040] Thirdly, the present invention provides a computing device, comprising:

[0041] Memory and processor;

[0042] The memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions. When the computer-executable instructions are executed by the processor, they implement the steps of the adaptive suppression method for commutation failure of the multi-infeed HVDC transmission system based on energy storage.

[0043] Fourthly, the present invention provides a computer-readable storage medium storing computer-executable instructions that, when executed by a processor, implement the steps of the adaptive suppression method for commutation failure in the energy storage-based multi-infeed high-voltage direct current transmission system.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention incorporates an energy storage system into a multi-infeed high-voltage direct current transmission system, and performs adaptive coordinated control based on the reactive power of the energy storage system when commutation failure occurs. This combines the advantages of energy storage in rapidly providing reactive power, thereby improving the efficiency of commutation failure suppression. The fault diagnosis module more effectively identifies the occurrence of commutation failure, ensuring that the control of the energy storage system has a good suppression effect and a fast response capability. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. 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.

[0046] Figure 1 This is a schematic diagram of a multi-infeed high-voltage direct current transmission system and energy storage main circuit according to an embodiment of the present invention;

[0047] Figure 2 This is a schematic diagram of the inverter / converter control circuit of a high-voltage direct current transmission system according to an embodiment of the present invention;

[0048] Figure 3 This is a schematic diagram of the inverter control circuit of an energy storage system according to an embodiment of the present invention;

[0049] Figure 4 This is a schematic diagram of an adaptive control method for suppressing commutation failure in a multi-infeed HVDC transmission system based on energy storage, according to an embodiment of the present invention.

[0050] Figure 5 This is a schematic diagram of an adaptive process for suppressing commutation failure in a multi-infeed HVDC transmission system based on energy storage, according to an embodiment of the present invention.

[0051] Figure 6 This diagram illustrates a comparison of experimental results between a conventional method for suppressing commutation failure and the adaptive control method for commutation failure described in an embodiment of the present invention.

[0052] The meanings of the characters and numbers appearing in the attached diagram are as follows: 1 represents the first LCC-HVDC DC transmission system; 2 represents the rectifier-side synchronous motor; 3 represents the equivalent impedance of the rectifier-side AC line; 4 represents the rectifier-side filter; 5 represents the rectifier-side transformer; 6 represents the rectifier-side unit; 7 represents the DC transmission line; 8 represents the inverter; 9 represents the inverter-side transformer; 10 represents the inverter-side filter; 11 represents the equivalent impedance of the LCC inverter-side AC line; and 12 represents the LCC inverter-side synchronous motor. 13 represents the second LCC-HVDC DC transmission system; 14 represents the first tie line; 15 represents the second tie line; 16 represents the third tie line; 17 represents the energy storage system; 18 represents the energy storage module; 19 represents the DC-DC converter; 21 represents the inverter; 22 represents the inverter-side equivalent impedance; 23 represents the inverter-side synchronous motor; 24 represents the first first-order inertial element; 25 represents the first inverting adder; 26 represents the low-voltage current limiting controller; 27 represents the minimum value selector; 28 represents the table. 29 represents the compensation resistor, 30 represents the second first-order inertial element, 31 represents the second inverting adder, 32 represents the third inverting adder, 33 represents the first PI controller, 34 represents the current deviation controller, 35 represents the minimum turn-off angle measurement module, 36 represents the fourth inverting adder, 37 represents the second PI controller, 38 represents the second maximum value selector, 39 represents the LCC inverter control circuit, 40 represents the fifth inverting adder, 41 represents the third PI controller, 42 represents the sixth inverting adder, 43 represents the fourth PI controller, 44 represents the current inner loop controller, 45 represents the inverse Park converter, 46 represents the PWM modulator, 47 represents the energy storage system inverter control circuit, 48 represents the fault judgment module, 49 represents the voltage judgment module, 50 represents the first reactive power reference value generator, 51 represents the second reactive power reference value generator, 52 represents the third reactive power reference value generator, and 53 represents the improved BESS transient reactive power control circuit system.

[0053] U mes I is the DC voltage of the LCC inverter. mes It is the DC current of the LCC inverter, γ mes The turn-off angle measured by the inverter, I orde It is the input current reference value (pu), I ord_rec This is the DC current reference value for the rectifier, β. inv It is the inverter's firing angle reference value, P ref It is the reference active power, Q ref P is the reference reactive power, Q is the active power, and i is the reactive power. gd and i gq Let u be the d and q components of the inverter output current. gd and u gq This represents the d-q modulation of the DC voltage, where U is the measured AC voltage value. set γ is the set voltage threshold, γ is the turn-off angle, k1 is the first droop coefficient, and k2 is the second droop coefficient. Detailed Implementation

[0054] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0055] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0056] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0057] This invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of this invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not adhering to the usual scale. Furthermore, the schematic diagrams are merely examples and should not be construed as limiting the scope of protection of this invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0058] Furthermore, in the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the system 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. In addition, the terms "first," "second," or "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0059] Unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" in this invention should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; similarly, they can refer to mechanical connections, electrical connections, or direct connections, or indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0060] Example 1

[0061] The Chinese translations of the English terms used in this invention are as follows:

[0062] LCC-HVDC (Line Commutated Converter High Voltage Direct Current System): A high-voltage direct current transmission system based on a linear rectifier converter;

[0063] PI (Proportional Integral): Proportional Integral;

[0064] PWM (Pulse Width Modulation): Pulse Width Modulation.

[0065] Reference Figures 1-5 As one embodiment of the present invention, a multi-infeed high-voltage direct current transmission system based on energy storage is provided, comprising:

[0066] The first LCC-HVDC DC transmission system, the second LCC-HVDC DC transmission system, and the energy storage system;

[0067] The first LCC-HVDC DC transmission system and the second LCC-HVDC DC transmission system are connected via a first tie line, the first LCC-HVDC DC transmission system and the energy storage system are connected via a second tie line, and the second LCC-HVDC DC transmission system and the energy storage system are connected via a third tie line.

[0068] The first LCC-HVDC DC transmission system and the second LCC-HVDC DC transmission system are used for long-distance, low-loss power transmission, and the control circuit ensures the power transmission stability of a single line.

[0069] Energy storage systems are used to provide dynamic reactive power support for multi-infeed HVDC transmission systems and suppress commutation failures.

[0070] Furthermore, the specific contents of the first LCC-HVDC DC transmission system and the second LCC-HVDC DC transmission system are completely identical, including:

[0071] The system includes a rectifier-side synchronous motor, an equivalent impedance of the rectifier-side AC line, a rectifier-side filter, a rectifier-side transformer, a rectifier-side converter, a DC transmission line, an inverter-side unit, an LCC inverter-side transformer, an inverter-side filter, an LCC inverter-side AC line equivalent impedance, an LVV inverter-side synchronous motor, and an LCC inverter control circuit, wherein the inverter-side converter is controlled by the converter control circuit.

[0072] The inverter-side converter control circuit includes a first first-order inertial element, a first inverting adder, a low-voltage current limiting controller, a minimum value selector, a second first-order inertial element, a compensation resistor, a second inverting adder, a third inverting adder, a first PI controller, a current deviation controller, a minimum turn-off angle measurement module, a fourth inverting adder, a second maximum value selection module, a second PI controller, and a second maximum value selector.

[0073] The input of the first-order inertial element is the voltage measurement value, and the output signal is sent to the positive input terminal of the first inverting adder. The other input signal of the first inverting adder comes from the compensation resistor. The output signal of the first inverting adder is sent to the low-voltage current limiting controller. The output signal of the low-voltage current limiting controller is sent to the minimum value selector. The other input signal of the minimum value selector is the current setting value. The output signal of the minimum value selector is sent to the positive terminal of the second inverting adder.

[0074] The input signal of the second first-order inertial element is the measured current value. The output signal of the first-order inertial element is the compensation resistor and the negative terminal of the second inverting adder. The output signal of the second inverting adder is sent to the positive terminal of the third inverting adder and the current deviation control module. The negative input of the third inverting adder is 0.1. The output signal of the third inverting adder is sent to the first PI controller. The output signal of the first PI controller is sent to the second maximum value selector.

[0075] The minimum shut-off angle measurement module receives the measured shut-off angle as its input signal. Its output signal is sent to the negative terminal of the fourth inverting adder. The first positive input signal of the fourth inverting adder is the reference value of the shut-off angle. The second positive input signal of the fourth inverting adder is the output signal of the current deviation controller. The fourth inverting adder outputs a signal to the first maximum value selector. The other input signal of the first maximum value selector is -30°. The first maximum value selector outputs a signal to the second PI controller. The second PI controller outputs a signal to the second maximum value selector. The second maximum value selector outputs a signal to the grid-side converter.

[0076] Furthermore, the energy storage system includes an energy storage module, a DC-DC converter, a DC-DC converter control circuit, an inverter, an inverter control circuit, an inverter-side equivalent impedance, and an inverter-side synchronous motor;

[0077] The inverter control circuit mainly includes a fifth inverting adder, a third PI controller, a sixth inverting adder, a fourth PI controller, a current inner loop controller, an inverse Park converter, and a PWM modulator.

[0078] The positive input of the fifth inverting adder is the active power reference value, the negative input of the fifth inverting adder is the actual active power value, the output signal of the fifth inverting adder is sent to the third PI controller, and the output signal of the third PI controller is sent to the current inner loop controller.

[0079] The negative terminal of the sixth inverting adder is the reactive power reference value, and the positive terminal input signal of the sixth inverting adder is the actual reactive power value. The output signal of the sixth inverting adder is sent to the fourth PI controller, the output signal of the fourth PI controller is sent to the current inner loop controller, the output signal of the current inner loop controller is sent to the first input of the inverted Park converter, the second input of the inverted Park converter is the voltage phase angle θ, the output signal of the inverted Park converter is sent to the PWM modulation module, and the output signal of the PWM modulation module is sent to the DC-DC converter.

[0080] Furthermore, the BESS transient reactive power control system based on energy storage multi-infeed HVDC transmission system is also improved. The improved BESS transient reactive power control system includes a fault judgment module, a voltage judgment module, a first reactive power reference value generator, a second reactive power reference value generator, and a third reactive power reference value generator.

[0081] The input values ​​of the fault judgment module are AC voltage and turn-off angle. The output signal is sent to the third reactive power reference value generator and the voltage judgment module. The output of the voltage judgment module is sent to the first reactive power reference value generator and the second reactive power reference value generator. The output signals of the first reactive power reference value generator, the second reactive power reference value generator and the third reactive power reference value generator are sent to the negative terminal of the sixth inverting adder.

[0082] Example 2

[0083] Reference Figures 1-5 Based on the previous embodiment, this embodiment provides an adaptive suppression method for commutation failure in a multi-infeed HVDC transmission system based on energy storage. The method mainly consists of a fault detection module and a reactive power reference value generation module. It is primarily applied in the energy storage controller, combining the LCC-HVDC grid connection point voltage and the LCC inverter's turn-off angle during operation, including:

[0084] S1: The MIDC system consists of two high-voltage direct current transmission lines. Based on the relevant parameters of the CIGRE DC main circuit, namely the relevant parameters of the first LCC-HVDC DC transmission system and the second LCC-HVDC DC transmission system, the main circuit model of MIDC was constructed in PSCAD.

[0085] S2: Based on the main circuit model of MIDC and the relevant parameters of the improved BESS transient reactive power control system, design the control circuit of MIDC. When the control circuit of MIDC is running normally, the inverter adopts constant extinction angle control. During the transient process, the inverter side can achieve smooth switching between constant extinction angle control and constant current control through current deviation control.

[0086] S3: Based on the main circuit parameters of the energy storage system, a main circuit model is established. This invention uses a mean value model to model the DC-DC converter. Its simplified circuit can be equivalent to a Boost circuit and a DC parallel capacitor, as follows:

[0087]

[0088] Among them, i L U is the boost inductor current; batt U is the output voltage of the lithium battery array. dc It is the DC voltage of the inverter, i dc It is the DC current of the inverter.

[0089] The grid-connected inverter is modeled using a mean value model, and is represented as follows:

[0090]

[0091] Among them, i gd and i gq Let d and q be the output current of the inverter, and e be the output current of the inverter. d e q The d and q components of the AC voltage on the grid side; u gd and u gq d and q modulation of DC voltage; L is the inductance of the Boost circuit; L r Lr is the inverter-side filter inductance; v iD is the single-phase AC voltage on the inverter side. i is the single-phase modulation ratio; i takes values ​​of abc.

[0092] S4: Based on the main circuit model of the energy storage system and the relevant parameters of the improved BESS transient reactive power control system, design the inverter control circuit of the energy storage system.

[0093] S5: Based on the aforementioned models and power, the actual voltage value of the multi-infeed HVDC transmission system is compared with the set voltage threshold, and the actual value of the turn-off angle is compared with the set turn-off angle threshold. According to the comparison results and voltage drop range, the corresponding reactive power reference value generator is triggered to output reactive power. The reactive power is used to adaptively suppress the commutation failure of the multi-infeed HVDC system.

[0094] First, compare the actual voltage value with U. set =0.9pu is compared, and the actual value of the shutdown angle is compared with 35°;

[0095] When the voltage is less than or equal to 0.9 pu and the actual shutdown angle is less than or equal to 35°, the reactive power compensation command is segmented according to the percentage of voltage drop. When the voltage drop is between 0 and 0.3 pu, the first reactive power reference generator is triggered, and the output reactive power is...

[0096] Q ref =k1×Q set ×(1-U)

[0097] Among them, Q ref The reactive power reference value is the input to the inverter control circuit of the energy storage system; k1 is the first droop coefficient, Q set The initial reactive power reference value input to the inverter control circuit of the energy storage system during transient states is set to 1, and U is the voltage value at the grid connection point of the energy storage system.

[0098] When the voltage drop is between 0.3 pu and 0.9 pu, the second reactive power reference generator is triggered and starts, outputting reactive power of...

[0099] Q ref =k2×Q set ×U

[0100] Among them, Q ref Q is the reactive power reference value input to the inverter control circuit of the energy storage system; k2 is the second droop coefficient, Q set The initial reactive power reference value input to the inverter control circuit of the energy storage system during transient states is set to 1, and U is the voltage value at the grid connection point of the energy storage system.

[0101] Under other conditions, the third reactive power reference value generator is triggered to start.

[0102] Q ref =0

[0103] This embodiment also provides a computing device applicable to the adaptive suppression method for commutation failure in multi-infeed HVDC transmission systems based on energy storage, including:

[0104] The system includes a memory and a processor. The memory stores computer-executable instructions, and the processor executes the computer-executable instructions to implement the energy storage-based multi-infeed high-voltage direct current transmission system as proposed in the above embodiments.

[0105] This embodiment also provides a storage medium storing a computer program that, when executed by a processor, implements the adaptive suppression method for commutation failure in a multi-infeed HVDC transmission system based on energy storage, as proposed in the above embodiments.

[0106] The storage medium proposed in this embodiment and the adaptive suppression method for commutation failure in a multi-infeed HVDC transmission system based on energy storage proposed in the above embodiments belong to the same inventive concept. Technical details not described in detail in this embodiment can be found in the above embodiments, and this embodiment has the same beneficial effects as the above embodiments.

[0107] Based on the above description of the implementation methods, those skilled in the art can clearly understand that the present invention can be implemented using software and necessary general-purpose hardware, and of course, it can also be implemented using hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk, or optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of the various embodiments of the present invention.

[0108] Example 3

[0109] Reference Figure 6 Based on the previous two embodiments, this embodiment scientifically demonstrates an adaptive suppression method for commutation failure in a multi-infeed HVDC transmission system based on energy storage, and verifies the effectiveness of the invention.

[0110] This invention is based on a multi-infeed DC transmission system and related simulations were performed. The power of the rectifier-side synchronous motor 19 is 1000MW and the output voltage is 345kV. It is connected to the rectifier-side transformer 20 through the equivalent impedance of the rectifier-side AC line. The rectifier-side transformer 20 converts the voltage value of 345kV to 500kV. The reactive power generated by the rectifier-side filter accounts for 50% of the total transmitted power. The rectifier-side converter converts the 500kV AC to 500kV DC voltage.

[0111] The DC current is 2kA, the DC line length is 100km, the inverter-side converter transforms the 500kV voltage to 345kV AC voltage, the LCC inverter-side transformer transforms the 345kV voltage to 230kV AC voltage, and the LCC inverter-side synchronous motor voltage is 220kV. The energy storage system can generate 600MVar of reactive power. The conventional control method is that when a voltage drop is detected, the reactive power reference value changes from 0 to 1pu.

[0112] Based on the simulation settings, the simulation results were tested under the condition of a ground fault on the inverter side of the first LCC-HVDC DC transmission system. A ground fault was set on the inverter side of the first LCC-HVDC DC transmission system with a start time of 1.5s, a duration of 1s, and a ground inductance of 0.01H.

[0113] Simulation results are as follows Figure 6 As shown, Figure 6 The performance of the strategy of this invention and the conventional strategy during faults was compared. The conventional strategy exhibits large voltage drops or current oscillations during faults and slow recovery. In contrast, the strategy of this invention maintains system stability better during faults, with smaller voltage drops, reduced oscillations, or faster recovery times.

[0114] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A multi-infeed high-voltage direct current transmission system based on energy storage, characterized in that, It includes a first LCC-HVDC DC transmission system, a second LCC-HVDC DC transmission system, and an energy storage system; The first LCC-HVDC DC transmission system and the second LCC-HVDC DC transmission system are connected via a first tie line, the first LCC-HVDC DC transmission system and the energy storage system are connected via a second tie line, and the second LCC-HVDC DC transmission system and the energy storage system are connected via a third tie line. The first LCC-HVDC DC transmission system and the second LCC-HVDC DC transmission system are used for long-distance, low-loss power transmission, and the control circuit ensures the power transmission stability of a single line. Energy storage systems are used to provide dynamic reactive power support for multi-infeed HVDC transmission systems and suppress commutation failures.

2. The multi-infeed HVDC transmission system based on energy storage as described in claim 1, characterized in that, It also includes transient reactive power control systems; The transient reactive power control system includes a fault judgment module, a voltage judgment module, a first reactive power reference value generator, a second reactive power reference value generator, and a third reactive power reference value generator.

3. The multi-infeed HVDC transmission system based on energy storage as described in claim 2, characterized in that, Both the first LCC-HVDC DC transmission system and the second LCC-HVDC DC transmission system include: synchronous motors, equivalent impedance, filters, transformers, converters, and corresponding transmission lines and control circuits; The converter is controlled by a converter control circuit, which includes a first first-order inertial element, a first inverting adder, a low-voltage current limiting controller, a minimum value selector, a second first-order inertial element, a compensation resistor, a second inverting adder, a third inverting adder, a first PI controller, a current deviation controller, a minimum turn-off angle measurement module, a fourth inverting adder, a second maximum value selection module, a second PI controller, and a second maximum value selector.

4. The multi-infeed HVDC transmission system based on energy storage as described in claim 3, characterized in that, The energy storage system includes an energy storage module, a DC-DC converter, a DC-DC converter control circuit, an inverter, an inverter control circuit, an inverter-side equivalent impedance, and an inverter-side synchronous motor. The inverter control circuit includes a fifth inverting adder, a third PI controller, a sixth inverting adder, a fourth PI controller, a current inner loop controller, an inverted Park converter, and a PWM modulator.

5. The multi-infeed HVDC transmission system based on energy storage as described in claim 4, characterized in that, The fault diagnosis module includes: The input values ​​of the fault judgment module are AC voltage and turn-off angle. The output signal is sent to the third reactive power reference value generator and the voltage judgment module. The output of the voltage judgment module is sent to the first reactive power reference value generator and the second reactive power reference value generator. The output signals of the first reactive power reference value generator, the second reactive power reference value generator and the third reactive power reference value generator are sent to the negative terminal of the sixth inverting adder.

6. An adaptive suppression method for commutation failure applied to multi-infeed HVDC transmission systems based on energy storage, characterized in that, include: Based on the parameters of the first LCC-HVDC DC transmission system and the second LCC-HVDC DC transmission system, a main circuit model of MIDC is established; Based on the main circuit model of MIDC and combined with the relevant parameters of the transient reactive power control system, the control circuit of MIDC is designed. When the control circuit of MIDC is running normally, the inverter adopts constant extinction angle control. During the transient process, the inverter side of MIDC uses current deviation control to smoothly switch between constant extinction angle control and constant current control. Based on the main circuit parameters of the energy storage system, a main circuit model is established. Based on the main circuit model and the relevant parameters of the transient reactive power control system, the inverter control circuit of the energy storage system is designed. Based on various models and circuit designs, the actual voltage value of the multi-infeed HVDC transmission system is compared with the set voltage threshold, and the actual value of the turn-off angle is compared with the set turn-off angle threshold. According to the comparison results and voltage drop range, the corresponding reactive power reference value generator is triggered to output reactive power. The reactive power is used to adaptively suppress the commutation failure of the multi-infeed HVDC system.

7. The adaptive suppression method for commutation failure in a multi-infeed HVDC transmission system based on energy storage as described in claim 6, characterized in that, Adaptive suppression of commutation failure in multi-infeed HVDC systems using reactive power, including: When the voltage is less than or equal to the third voltage and the actual value of the turn-off angle is less than or equal to the set turn-off angle threshold, the reactive power compensation command is divided according to the percentage of voltage drop. When the voltage drop is between the first voltage and the second voltage, the first reactive power reference generator is triggered and starts, and the output reactive power is expressed as: Q ref =k1×Q set ×(1-U) Among them, Q ref The reactive power reference value is the input to the inverter control circuit of the energy storage system; k1 is the first droop coefficient, Q set The initial reactive power reference value input to the inverter control circuit of the energy storage system during transients is set to 1, and U is the voltage value at the grid connection point of the energy storage system. When the voltage drop is between the second and third voltages, the second reactive power reference generator is triggered and starts, and the output reactive power is expressed as: Q ref =k2×Q set ×U Among them, Q ref Q is the reactive power reference value input to the inverter control circuit of the energy storage system; k2 is the second droop coefficient, Q set The initial reactive power reference value input to the inverter control circuit of the energy storage system during transient states is set to 1, and U is the voltage value at the grid connection point of the energy storage system.

8. The adaptive suppression method for commutation failure in a multi-infeed HVDC transmission system based on energy storage as described in claim 6, characterized in that, The main circuit model includes: The converter is modeled using a mean-valued model, equivalent to a boost circuit and a DC parallel capacitor, as follows: Among them, i L U is the boost inductor current; batt U is the output voltage of the lithium battery array. dc It is the DC voltage of the inverter, i dc It is the DC current of the inverter. The grid-connected inverter is modeled using a mean value model, and is represented as follows: Among them, i gd and i gq Let d and q be the output current of the inverter, and e be the output current of the inverter. d e q The d and q components of the AC voltage on the grid side; u gd and u gq d and q modulation of DC voltage; L is the inductance of the Boost circuit; L r Lr is the inverter-side filter inductance; v i D is the single-phase AC voltage on the inverter side. i is the single-phase modulation ratio; i takes values ​​of abc.

9. An electronic device, comprising: Memory and processor; The memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions. When the computer-executable instructions are executed by the processor, they implement the steps of the adaptive suppression method for commutation failure of the multi-infeed HVDC transmission system based on energy storage as described in any one of claims 6 to 8.

10. A computer-readable storage medium storing computer-executable instructions that, when executed by a processor, implement the steps of the adaptive suppression method for commutation failure in a multi-infeed HVDC transmission system based on energy storage as described in any one of claims 6 to 8.

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