Networking type flexible direct current stabilization control improvement method, electronic equipment and medium

Abstract

The invention discloses a network construction type flexible direct current stabilization control improvement method, electronic equipment and a medium, and belongs to the technical field of new energy. The method comprises the following steps: designing a following control method of active reference power in virtual synchronous control, and enabling a flexible DC converter station to track the change of system generation power so as to maintain stable operation of a sending-end power grid; designing a network construction control mode smooth switching method in a flexible direct current starting stage so as to realize smooth switching of the network construction type converter from constant V / f control to virtual synchronous control; and designing a stabilization control method for improving the transient synchronization stability of the sending-out system, so that the network construction flexible direct current can actively accelerate and keep synchronous with the synchronous generator during the fault period. According to the invention, smooth switching of the network-forming converter from constant V / f control to virtual synchronous control can be realized, and stable starting of a new energy base containing a synchronous generator is supported; in addition, the networking flexible direct current can actively accelerate to keep synchronous with the synchronous generator during the fault period, and the transient synchronous stability of the system is improved.

Description

Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to an improved method for grid-type flexible direct current stabilization control, electronic equipment and a medium. Background Art

[0002] In recent years, the country has accelerated the planning and construction of a number of new energy base projects in deserts, Gobi and wasteland areas, mainly large-scale wind power and photovoltaic bases, supplemented by hydropower and thermal power. Due to the weak power grid in deserts, Gobi and wasteland areas, the small number of local conventional power sources, and the difficulty of conventional transmission methods to support the long-distance transmission of new energy from large bases. As a new generation of direct current transmission technology, flexible direct current transmission has the ability to build a network and can operate without the support of conventional power sources. It is more suitable for long-distance transmission scenarios of new energy bases with complex and changeable operating conditions.

[0003] This type of external transmission system generally contains a small amount of synchronous power or has weak continuity with the local power grid. Therefore, the flexible DC converter station in the network operation often needs to adopt virtual synchronous generator control (VSG) to run in parallel with the synchronous generator to jointly support the safety and stability of the sending-end power grid. However, virtual synchronous control requires external active reference power setting, while the power generation of large-scale new energy bases is in a continuous and large-scale change, requiring the DC transmission power to follow the power generation change, which is contradictory. In addition, the capacity of flexible DC is much larger than the synchronous generator in the system. How to give full play to the stable regulation ability of flexible DC and improve the synchronous stability level of the system under fault conditions is also a problem that needs to be solved. Summary of the invention

[0004] In order to solve at least one of the technical problems existing in the prior art to a certain extent, the purpose of the present invention is to provide an improved method, electronic equipment and medium for grid-connected flexible direct current stabilization control suitable for transmission from new energy bases.

[0005] The first technical solution adopted by the present invention is:

[0006] An improved method for grid-type flexible direct current stabilization control comprises the following steps:

[0007] Design the active reference power following control method in virtual synchronous control (VSG control) so that the flexible DC converter station can track the changes in system power generation to maintain the stable operation of the sending-end power grid;

[0008] A smooth switching method of the grid-forming control mode during the flexible DC startup phase is designed to achieve smooth switching of the grid-forming converter from constant V / f control to virtual synchronous control.

[0009] A stabilizing control method is designed to improve the transient synchronous stability of the transmission system, so that the flexible DC can actively accelerate and keep synchronization with the synchronous generator during the fault, so as to reduce the maximum power angle difference between the synchronous power sources and improve the transient synchronous stability of the system.

[0010] Furthermore, the active power equation and reactive power equation in the existing flexible DC virtual synchronous control are:

[0011]

[0012] Where, J is the moment of inertia; Δω=ω-1 is the difference between the angular velocity of the synchronous machine and the rated angular velocity; P e is the active power actually output by the converter station, P ref is the active reference power command value; D is the damping coefficient; T q is the reactive loop integral coefficient; ΔE is the virtual electromotive force correction value output by the reactive loop, which is added to the initial value of the virtual electromotive force E 0 After that, the virtual electromotive force reference value E required by the d-axis positive sequence voltage loop can be obtained; Q e is the reactive power flowing into the converter station; Q ref is the reactive power reference value; D q is the reactive power-voltage droop coefficient; E ref is the voltage reference value.

[0013] Furthermore, the design of the following control method of active reference power in virtual synchronous control includes:

[0014] By tracking the power changes on the DC side of the converter station, the active reference power command value is modified, so that the converter station can respond to the output fluctuations of the new energy station in a timely manner; the expression of the modified active reference power command value is:

[0015]

[0016] P dc =U dc I dc

[0017] Where G is the gain coefficient of the first-order inertia link; T is the time constant of the first-order inertia link; P dc is the DC side power of the converter station, and the DC side voltage U of the converter station is obtained by measurement. dc and current I dc Multiply them together to get .

[0018] Furthermore, the network control mode smooth switching method includes an active control loop switching mode and a reactive control loop switching mode; both the active control loop switching mode and the reactive control loop switching mode use a switch signal S 0 To control the switching, its action logic is:

[0019]

[0020] Furthermore, the specific working mode of the method for smoothly switching the networking control mode is as follows:

[0021] Set the switch signal S before the system starts 0 =0, at this time, the input of the rotation inertia integral link of the active loop and the reactive loop integral link in the flexible DC control is set to zero, which is equivalent to starting the sending-end converter station with constant V / f control to establish the sending-end system voltage and frequency;

[0022] The power supply in the sending-end system is put into operation in sequence, so that the synchronous units and the new energy station are put into operation and the power is transmitted to the sending-end converter station;

[0023] After all power supplies in the system are connected to the grid and running smoothly, set the switch signal S 0 =1 switches the sending-end converter station to virtual synchronous control;

[0024] Among them, the instantaneous reactive power Q output by the converter station at the switching moment e0 The power reference value of the reactive power loop is set as the virtual synchronous control, and the reference value of the active power loop is obtained by the following control method of the active reference power.

[0025] Furthermore, the stabilizing control method designed to improve the transient synchronization stability of the transmission system includes:

[0026] Improvements are made to flexible DC active power control;

[0027] Improvements are made to the fault ride-through strategy of photovoltaic converters.

[0028] Furthermore, the improvement on flexible DC active power control includes:

[0029] By switching the signal S 1 Control transient enhancement, its action logic is:

[0030]

[0031] The specific control method of transient enhancement is as follows:

[0032] Detect the bus voltage of the sending-end converter station. When the bus voltage of the sending-end converter station drops below 0.9pu, it is determined that the sending-end converter station enters the low voltage ride-through state. At this time, the active follow-up control of the virtual synchronous control of the sending-end converter station is stopped, and the switch signal S 1 Switching from 0 to 1, the active reference power command value of the active power loop is changed to be given and adjusted according to the following rules:

[0033] P r 'ef =C·P ref0

[0034]

[0035] Where P ref0 is the active reference power command value of the VSG active power loop in the steady state before the fault; U HVDC is the AC bus voltage of the flexible DC converter station of the sending-end power grid; C is the active power command adjustment coefficient. When the voltage drops deeply, the active power reference value is reversed, so that the VSG of the sending-end converter station also enters the acceleration state during the fault period, which can further reduce the first swing power angle difference between the VSG and the hydropower unit and enhance the transient synchronization stability of the system.

[0036] Furthermore, the improvement of the photovoltaic converter fault ride-through strategy includes:

[0037] When it is detected that the voltage at the station PCC point drops below 0.9pu, the new energy station enters the fault ride-through state. During the fault period, the d and q axis current command values ​​are determined by the following formula:

[0038]

[0039]

[0040] In the formula, i dref_lvrt and i qref_lvrt are the d-axis and q-axis reference current command values ​​during the low voltage ride-through period of the new energy station; i dref0 is the steady-state d-axis current reference value of the new energy station before the fault occurs; V pcc_f is the PCC point voltage of the new energy station during the fault period; V pcc is the voltage at the PCC point of the station.

[0041] The second technical solution adopted by the present invention is:

[0042] An electronic device comprises a processor and a memory, wherein the memory stores at least one instruction, at least one program, a code set or an instruction set, and the at least one instruction, the at least one program, the code set or the instruction set are loaded and executed by the processor to implement an improved method for grid-type flexible direct current stabilization control as described above.

[0043] The third technical solution adopted by the present invention is:

[0044] A computer-readable storage medium stores at least one instruction, at least one program, a code set or an instruction set, wherein the at least one instruction, the at least one program, the code set or the instruction set is loaded and executed by a processor to implement an improved method for grid-type flexible direct current stabilization control as described above.

[0045] The fourth technical solution adopted by the present invention is:

[0046] A computer program product or a computer program, the computer program product or the computer program includes computer instructions, the computer instructions are stored in a computer-readable storage medium. A processor of a computer device can read the computer instructions from the computer-readable storage medium, and the processor executes the computer instructions, so that the computer device executes the above-mentioned improved method for grid-type flexible direct current stabilization control.

[0047] The beneficial effects of the present invention are as follows: the present invention can realize the smooth switching of the grid-type converter from constant V / f control to virtual synchronous control through the flexible DC active power following control and smooth starting strategy, and support the smooth starting of the new energy base containing synchronous generators. In addition, through the active control strategy design of the grid-type flexible DC and photovoltaic station during the fault period, the flexible DC is actively accelerated, the synchronization capability of the synchronous power supply and the step power supply in the system is improved, and the transient process of the system is shortened. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the embodiments of the present invention or the drawings of related technical solutions in the prior art are introduced below. It should be understood that the drawings introduced below are only for the convenience of clearly describing some embodiments of the technical solutions of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0049] Figure 1 Schematic diagram of a virtual synchronous control active ring structure for forming a flexible direct current network in an embodiment of the present invention;

[0050] Figure 2 Schematic diagram of a virtual synchronous control reactive ring structure for forming a flexible direct current network in an embodiment of the present invention;

[0051] Figure 3 Schematic diagram of an improved strategy for low voltage ride through control in a photovoltaic station according to an embodiment of the present invention;

[0052] Figure 4 is a flow chart of a method for smoothly switching different control modes of a grid-connected converter in an embodiment of the present invention;

[0053] Figure 5is a system model diagram for verifying the control method in an embodiment of the present invention;

[0054] Figure 6 is a power angle difference curve diagram of the VSG and the hydropower unit Hydro1 before and after the improved control is applied in the embodiment of the present invention;

[0055] Figure 7 is a bus voltage curve diagram of the sending-end converter station before and after the improved control is applied in the embodiment of the present invention;

[0056] Figure 8 is an active power curve diagram of the sending-end converter station before and after the improved control is applied in the embodiment of the present invention;

[0057] Fig. 9 It is a flowchart of the steps of an improved method for grid-type flexible direct current stabilization control in an embodiment of the present invention. DETAILED DESCRIPTION

[0058] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and are not to be construed as limitations of the present invention. For the step numbers in the following embodiments, they are only provided for the convenience of explanation, and the order between the steps is not limited in any way, and the execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

[0059] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0060] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0061] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0062] Terminology explanation:

[0063] PCC point voltage: Point of Common Coupling voltage.

[0064] In view of the existing technical problems, the present invention proposes a flexible direct current stabilization control method for the transmission system of a new energy base containing a synchronous power supply or a weakly interconnected system. The proposed improvements include: a following control method for active reference power in virtual synchronous control (VSG control) is proposed, so that the flexible direct current converter station can track the changes in the system's power generation power and maintain the smooth operation of the power grid at the sending end; a smooth switching method for the control mode of the flexible direct current in the startup phase is proposed, which can establish a stable voltage and frequency in the transmission system containing a synchronous power supply; a control strategy for improving the transient synchronization stability of the transmission system is proposed, so that the flexible direct current in the network can actively accelerate to keep in sync with the synchronous generator during a fault, reduce the maximum power angle difference between the synchronous power supplies, and improve the transient synchronization stability of the system.

[0065] Example 1

[0066] like Fig. 9 As shown, this embodiment provides an improved method for grid-type flexible direct current stabilization control, comprising the following steps:

[0067] S1. Design a following control method for active reference power in virtual synchronous control (VSG control) so that the flexible DC converter station can track the changes in system power generation to maintain stable operation of the sending-end power grid;

[0068] S2. Design a smooth switching method for the grid-forming control mode during the flexible DC startup phase to achieve smooth switching of the grid-forming converter from constant V / f control to virtual synchronous control;

[0069] S3. Design a stabilizing control method to improve the transient synchronization stability of the transmission system, so that the flexible DC network can actively accelerate and keep synchronization with the synchronous generator during the fault, so as to reduce the maximum power angle difference between the synchronous power sources and improve the transient synchronization stability of the system.

[0070] The method of this embodiment proposes a flexible direct current active power following control and smooth starting strategy based on virtual synchronous control, which has the following features: a method for smooth switching of the control mode of the grid-forming converter in the startup phase, which can realize the smooth switching of the grid-forming converter from constant V / f control to virtual synchronous control, and support the smooth starting of the new energy base containing synchronous generators; a method for setting the flexible direct current reference power, and the flexible direct current converter station can track the output fluctuation of the new energy station. In addition, the method of this embodiment also proposes a stabilizing control method for improving the transient synchronous stability of the sending-end power supply. Its characteristics are: through the design of the active control strategy of the grid-forming flexible direct current and the photovoltaic station during the fault period, the flexible direct current is actively accelerated, the synchronization capability of the synchronous power supply and the step power supply in the system is improved, and the transient process of the system is shortened. The control improvement strategy of the method of this embodiment is explained in detail below in conjunction with the accompanying drawings.

[0071] (1) Active power following control and smooth start strategy based on virtual synchronous machine

[0072] The active power equation and reactive power equation in the existing flexible DC virtual synchronous control are shown in equation (1) and equation (2) respectively:

[0073]

[0074] In formula (1), J is the moment of inertia; Δω=ω-1 is the difference between the angular velocity of the synchronous machine and the rated angular velocity; P e is the active power actually output by the converter station, P ref is the reference active power command value; D is the damping coefficient. In formula (2), T q is the reactive loop integral coefficient; ΔE is the virtual electromotive force correction value output by the reactive loop, which is added to the initial value of the virtual electromotive force E 0 After that, the virtual electromotive force reference value E required by the d-axis positive sequence voltage loop can be obtained; Q e is the reactive power flowing into the converter station; Q ref is the reactive power reference value; D q is the reactive power-voltage droop coefficient; E ref is the voltage reference value.

[0075] The above steps can be adopted Figure 1 The control block diagram without the dashed box on the right is shown. Figure 1 The virtual boxes are control links added by the present invention, and the other links are existing links of the existing virtual synchronous control or photovoltaic low voltage ride-through control.

[0076] a) Active power following control

[0077] The embodiment of the present invention considers that the output of new energy stations has volatility and uncertainty, and proposes Figure 1The active power following control shown in the red box on the left. In equation (1), the active reference command calculation is determined by equations (3) and (4):

[0078]

[0079] P dc =U dc I dc (4)

[0080] Where P ref is the reference power of the input active loop; G is the gain coefficient of the first-order inertia link; T is the time constant of the first-order inertia link; P dc is the DC side power of the converter station, and the DC side voltage U of the converter station is obtained by measurement. dc and current I dc By tracking the power changes on the DC side of the converter station and modifying the active reference command value, the converter station can respond to the output fluctuations of the new energy station in a timely manner.

[0081] b) Smooth start control

[0082] The flexible DC smooth starting control strategy proposed in this embodiment includes: Figure 1 The active control loop shown in the green box switches and Figure 2 The reactive power control loop shown in the green box switches two parts.

[0083] Figure 1 and Figure 2 The green square S 0 To control the switching signal, its action logic follows formula (5):

[0084]

[0085] join Figure 4 , the control flow of the entire switching process is as follows:

[0086] 1) Set the switch signal S before starting 0 =0, at this time, the input of the active loop inertia integral link and the reactive loop integral link in the flexible DC control is set to zero, which is equivalent to starting the sending-end converter station with constant V / f control to establish the sending-end system voltage and frequency

[0087] 2) The power supply in the sending-end system is put into operation in sequence, so that the synchronous units and new energy stations are put into operation to transmit power to the sending-end converter station.

[0088] 3) After all power supplies in the system are connected to the grid and running smoothly, set the switch signal S 0 =1 Switch the sending-end converter station to virtual synchronous control, and the instantaneous reactive power Q output by the converter station at the moment of switching e0It is set as the power reference value of the virtual synchronous control reactive power loop, and the reference value of the active power loop is given by formula (3).

[0089] (2) Transient enhancement control method to improve the transient synchronization stability of the transmission system

[0090] The stabilization control method for the transient synchronization stability of the transmission system proposed in this embodiment includes: 1) Improvement of the flexible DC active power control, see Figure 1 The second blue box on the left; 2) Improvements to the fault ride-through strategy for PV converters, see Figure 3 The blue frame on the left side of the screen.

[0091] a) Improvement of flexible DC active power control

[0092] Figure 1 Medium S 1 is the switching signal of transient enhancement control, and its action logic follows formula (6):

[0093]

[0094] The specific control method of transient enhancement control is:

[0095] Detect the bus voltage of the sending-end converter station. When the bus voltage of the sending-end converter station drops below 0.9pu, it is determined that the sending-end converter station enters the low voltage ride-through state. At this time, the active follow-up control of the virtual synchronous control of the sending-end converter station is stopped, and the switch signal S 1 Switching from 0 to 1, the active loop reference power command is changed to be given and adjusted according to the following rules:

[0096] P r ' ef =C·P ref0 (7)

[0097]

[0098] Where P ref0 is the power reference command value of the VSG active loop in the steady state before the fault; U HVDC is the AC bus voltage of the flexible DC converter station of the sending-end power grid; C is the active power command adjustment coefficient. When the voltage drops deeply, the active power reference value is reversed, so that the VSG of the sending-end converter station also enters the acceleration state during the fault period, which can further reduce the first swing power angle difference between the VSG and the hydropower unit and enhance the transient synchronization stability of the system.

[0099] b) Improvement of PV inverter fault ride-through strategy

[0100] Improvement of active power control of photovoltaic converters during fault ride-through Figure 3When the voltage at the station PCC point is detected to drop below 0.9pu, the new energy station enters the fault ride-through state. During the fault period, the d and q axis current command values ​​are determined by equations (9) and (10):

[0101]

[0102] In the formula, i dref_lvrt and i qref_lvrt are the d-axis and q-axis reference current command values ​​during the low voltage ride-through period of the new energy station; i dref0 is the steady-state d-axis current reference value of the new energy station before the fault occurs; V pcc_f is the PCC point voltage of the new energy station during the fault period.

[0103] (3) Application test examples

[0104] In order to test the effectiveness and robustness of the control method of this embodiment, the following Figure 5 The system model shown is simulated and verified to compare the transient synchronous stability of the system before and after applying the improved control strategy:

[0105] Figure 5 In the model, the source side includes hydropower units and photovoltaic stations. The photovoltaic system is a single-stage photovoltaic converter, which adopts grid-following control based on the phase-locked synchronization principle and is boosted to 525kV via the AC collection line. The hydropower unit is connected to the photovoltaic power collection bus through a single-circuit long-distance transmission line. The hydropower unit is equipped with a prime mover, a speed regulator, an exciter, and a PSS. The hydropower power and the photovoltaic power are transmitted to the sending-end flexible DC converter station through multiple long-distance transmission lines.

[0106] The simulation condition is as follows: when the simulation time is t=0.5s, a three-phase ground short circuit fault occurs in one of the multiple AC lines of EO near the bus O, and the fault resistance is 0.001Ω. After the fault lasts for 0.1s, the circuit breakers at both ends of the line are actuated to cut off the faulty line.

[0107] The comparison control is:

[0108] 1) Before applying the improved control strategy: the related control loops of the sending-end flexible DC converter station and the photovoltaic station are: Figures 1 to 3 The control block diagram after removing the dashed frame.

[0109] 2) After applying the improved control strategy: the related control loops of the sending-end flexible DC converter station and the photovoltaic station adopt Figure 1 to Figure 2 Control block diagram.

[0110] The comparison simulation curve is as follows Figure 6 , Figure 7 and Figure 8 As shown, from Figure 6 to Figure 8 It can be seen that after the fault occurs, the system voltage drops rapidly, the active power of the synchronous generator, photovoltaic station and sending-end converter station drops to 0, and the power angle difference between the hydropower unit and the MMC virtual synchronous machine gradually increases. However, the improved control strategy can slow down this increasing trend and reduce the maximum power angle difference between the VSG and the synchronous generator.

[0111] After the faulty line was removed, the system voltage recovered rapidly, and the hydropower units and photovoltaic stations began to restore active output. In comparison, after applying the improved control strategy, the overshoot of the system active power recovery was well suppressed, and the voltage recovery speed was also increased. In the subsequent recovery process, the oscillation time and adjustment time of the system power and voltage were also greatly reduced.

[0112] In general, the simulation results show that the control strategy proposed in this patent can actively accelerate the VSG and effectively reduce the maximum power angle difference between the synchronous generator and the VSG. At the same time, under the action of the improved control strategy, the transient process of the system is significantly shortened and the damping of the system is significantly improved.

[0113] Then, based on the system transient synchronous stability evaluation index set described in parts (1)-(2), the maximum power angle difference of the system under the condition of a three-phase permanent N-1 fault lasting 0.1s and the critical fault removal time of the system under this fault are calculated before and after applying the improved control strategy. The results are shown in Tables 1 and 2:

[0114] Table 1: Maximum power angle difference of the system when a three-phase permanent N-1 fault lasts for 0.1s

[0115]

[0116] Table 2: System CCT under three-phase permanent N-1 fault

[0117]

[0118] It can be seen from Tables 1 and 2 that after applying the improved control strategy, the maximum power angle difference of the system is reduced and the system CCT is significantly extended.

[0119] In summary, combined with the simulation results and the quantitative analysis of the transient synchronization stability evaluation index set, the control strategy proposed in the present invention can significantly enhance the transient synchronization stability of the system.

[0120] Example 2

[0121] An embodiment of the present invention further provides an electronic device, the electronic device comprising a processor and a memory, the memory storing at least one instruction, at least one program, a code set or an instruction set, the at least one instruction, the at least one program, the code set or the instruction set being loaded and executed by the processor to implement the following Fig. 9An improved method for grid-type flexible DC stabilization control is shown.

[0122] It is understood that the memory may include a random access memory (RAM) or a read-only memory (ROM). Optionally, the memory includes a non-transitory computer-readable storage medium. The memory may be used to store instructions, programs, codes, code sets, or instruction sets. The memory may include a program storage area and a data storage area, wherein the program storage area may store instructions for implementing an operating system, instructions for at least one function, instructions for implementing the above-mentioned various method embodiments, etc.; the data storage area may store data created according to the use of the server, etc.

[0123] The processor may include one or more processing cores. The processor uses various interfaces and lines to connect the various parts of the entire server, and executes various functions of the server and processes data by running or executing instructions, programs, code sets or instruction sets stored in the memory, and calling data stored in the memory. Optionally, the processor can be implemented in at least one hardware form of digital signal processing (DSP), field programmable gate array (FPGA), and programmable logic array (PLA). The processor can integrate one or a combination of a central processing unit (CPU) and a modem. Among them, the CPU mainly processes the operating system and application programs; the modem is used to process wireless communications. It can be understood that the above-mentioned modem may not be integrated into the processor, but implemented separately through a chip.

[0124] Since the electronic device is an electronic device corresponding to an improved method for network-type flexible direct current stabilization control in an embodiment of the present invention, and the principle of solving the problem by the electronic device is similar to that of the method, the implementation of the electronic device can refer to the implementation process of the above-mentioned method embodiment, and the repeated parts will not be repeated.

[0125] Example 3

[0126] The embodiment of the present invention further provides a computer-readable storage medium, wherein the storage medium stores at least one instruction, at least one program, code set or instruction set, and the at least one instruction, the at least one program, the code set or instruction set is loaded and executed by a processor to implement the following Fig. 9 An improved method for grid-type flexible DC stabilization control is shown.

[0127] Those skilled in the art can understand that all or part of the steps in the various methods of the above embodiments can be completed by instructing related hardware through a program, and the program can be stored in a computer-readable storage medium, and the storage medium includes a read-only memory (ROM), a random access memory (RAM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), a one-time programmable read-only memory (OTPROM), an electronically erasable rewritable read-only memory (EEPROM), a compact disc (CD-ROM) or other optical disc storage, magnetic disk storage, magnetic tape storage, or any other computer-readable medium that can be used to carry or store data.

[0128] Since the storage medium is a storage medium corresponding to an improved method for grid-type flexible direct current stabilization control in an embodiment of the present invention, and the principle of solving the problem by the storage medium is similar to that of the method, the implementation of the storage medium can refer to the implementation process of the above-mentioned method embodiment, and the repeated parts will not be repeated.

[0129] Example 4

[0130] In some possible implementations, various aspects of the method of the embodiment of the present invention may also be implemented in the form of a program product, which includes a program code. When the program product is run on a computer device, the program code is used to enable the computer device to execute the steps of the improved method for grid-type flexible direct current stabilization control according to various exemplary embodiments of the present application described above in this specification. Among them, the executable computer program code or "code" for executing each embodiment may be written in a high-level programming language such as C, C++, C#, Smalltalk, Java, JavaScript, Visual Basic, structured query language (e.g., Transact-SQL), Perl, or in various other programming languages.

[0131] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0132] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0133] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable ordinary technicians in the field to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made based on the essence of the content of the present invention should be included in the protection scope of the present invention.

Claims

1. An improved method for grid-type flexible DC stabilization control, characterized in that: The following steps are involved: Design the following control method of active reference power in virtual synchronous control, so that the flexible DC converter station can track the changes of system power generation to maintain the stable operation of the sending-end power grid; A smooth switching method of the grid-forming control mode during the flexible DC startup phase is designed to achieve smooth switching of the grid-forming converter from constant V / f control to virtual synchronous control. A stabilizing control method is designed to improve the transient synchronization stability of the transmission system, so that the flexible direct current network can actively accelerate and keep synchronization with the synchronous generator during faults.

2. The improved method for grid-type flexible direct current stabilization control according to claim 1 is characterized in that: The active power equation and reactive power equation in flexible DC virtual synchronous control are: Where, J is the moment of inertia; Δω=ω-1 is the difference between the angular velocity of the synchronous machine and the rated angular velocity; P e is the active power actually output by the converter station, P ref is the active reference power command value; D is the damping coefficient; T q is the reactive loop integral coefficient; ΔE is the virtual electromotive force correction value output by the reactive loop. After adding it to the initial value of the virtual electromotive force E0, the virtual electromotive force reference value E required by the d-axis positive sequence voltage loop can be obtained; Q e is the reactive power flowing into the converter station; Q ref is the reactive power reference value; D q is the reactive power-voltage droop coefficient; E ref is the voltage reference value.

3. The improved method for grid-type flexible direct current stabilization control according to claim 2 is characterized in that: The design of the following control method of active reference power in virtual synchronous control includes: By tracking the power changes on the DC side of the converter station, the active reference power command value is modified, so that the converter station can respond to the output fluctuations of the new energy station in a timely manner; the expression of the modified active reference power command value is: Where G is the gain coefficient of the first-order inertia link; T is the time constant of the first-order inertia link; P dc is the DC side power of the converter station.

4. The improved method for grid-type flexible direct current stabilization control according to claim 1 is characterized in that: The network control mode smooth switching method includes an active control loop switching mode and a reactive control loop switching mode; both the active control loop switching mode and the reactive control loop switching mode use a switch signal S0 to control the switching, and the action logic is:

5. The improved method for grid-type flexible direct current stabilization control according to claim 4 is characterized in that: The specific working mode of the method for smooth switching of the networking control mode is as follows: Before the system is started, the switch signal S0 is set to 0. At this time, the input of the rotation inertia integral link of the active loop and the reactive loop integral link in the flexible DC control is set to zero, which is equivalent to starting the sending-end converter station with constant V / f control to establish the sending-end system voltage and frequency. The power supply in the sending-end system is put into operation in sequence, so that the synchronous units and the new energy station are put into operation and the power is transmitted to the sending-end converter station; After all power sources in the system are connected to the grid and running smoothly, set the switch signal S0 = 1 to switch the sending-end converter station to virtual synchronous control; Among them, the instantaneous reactive power Q output by the converter station at the switching moment e0 The power reference value of the reactive power loop is set as the virtual synchronous control, and the reference value of the active power loop is obtained by the following control method of the active reference power.

6. The improved method for grid-type flexible direct current stabilization control according to claim 1 is characterized in that: The stabilizing control method designed to improve the transient synchronization stability of the transmission system includes: Improvements are made to flexible DC active power control; Improvements are made to the fault ride-through strategy of photovoltaic converters.

7. The improved method for grid-type flexible DC stabilization control according to claim 6 is characterized in that: The improvement on flexible DC active power control includes: The transient enhancement is controlled by switching signal S1, and its action logic is: The specific control method of transient enhancement is as follows: The bus voltage of the sending-end converter station is detected. When the bus voltage of the sending-end converter station drops below 0.9pu, it is determined that the sending-end converter station enters the low voltage ride-through state. At this time, the active follow-up control of the virtual synchronous control of the sending-end converter station is stopped, and the switch signal S1 is switched from 0 to 1. The active reference power command value of the active power loop is changed to be given and adjusted according to the following rules: P r ' ef =C·P ref0 Where P ref0 is the active reference power command value of the VSG active power loop in the steady state before the fault; U HVDC is the AC bus voltage of the flexible DC converter station in the sending-end power grid; C is the active power command adjustment coefficient.

8. The improved method for grid-type flexible DC stabilization control according to claim 6 is characterized in that: The improvement of the photovoltaic converter fault ride-through strategy includes: When it is detected that the voltage at the station PCC point drops below 0.9pu, the new energy station enters the fault ride-through state. During the fault period, the d and q axis current command values ​​are determined by the following formula: In the formula, i dref_lvrt and i qref_lvrt are the d-axis and q-axis reference current command values ​​during the low voltage ride-through period of the new energy station; i dref0 is the steady-state d-axis current reference value of the new energy station before the fault occurs; V pcc_f is the PCC point voltage of the new energy station during the fault period; V pcc is the voltage at the PCC point of the station.

9. An electronic device, characterized in that: The electronic device includes a processor and a memory, wherein the memory stores at least one instruction, at least one program, a code set or an instruction set, and the at least one instruction, the at least one program, the code set or the instruction set is loaded and executed by the processor to implement the method described in any one of claims 1 to 8.

10. A computer-readable storage medium, characterized in that: The storage medium stores at least one instruction, at least one program, a code set or an instruction set, and the at least one instruction, the at least one program, the code set or the instruction set is loaded and executed by the processor to implement the method according to any one of claims 1 to 8.

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