HVDC hybrid system overvoltage coordinated control method for pole control and valve control of converter valve

Abstract

The application relates to a pole control-valve control coordinated control method for overvoltage of a flexible direct current system converter valve, which comprises the following steps: designing a switching frequency dynamic adjustment voltage equalization strategy in a valve control layer, and dynamically adjusting the switching frequency according to the average arm module capacitor voltage; designing a valve control imbalance protection direct triggering energy dissipation device input strategy, and directly triggering the input of the controllable self-recovery energy dissipation device when the valve control imbalance protection of any VSC converter valve in the hybrid cascade direct current system is actuated; and designing a converter valve overvoltage current limiting control strategy in the pole control layer, and increasing the power fed into the alternating current system by each converter when the capacitor voltage of any arm module of the any VSC converter valve is higher than a set value. The application can reduce the overvoltage level of the flexible direct current converter valve under alternating current system fault and valve side fault of the converter transformer, avoids fault ride-through failure or equipment damage, and can be widely applied to pole control-valve control coordinated control for overvoltage of a flexible direct current system converter valve.

Description

TECHNICAL FIELD

[0001] The application relates to a pole control-valve control coordinated control method for overvoltage of a flexible direct current system converter valve, and relates to the field of direct current transmission. BACKGROUND

[0002] In China, energy resources and load centers are inversely distributed, and the construction of a UHV backbone power grid needs to be steadily promoted to exert the transmission capacity of the UHV power grid. In some load centers such as the East China region, the demand for direct current feeding is increasing, but the dense feeding of external direct current will cause the electrical distance between converter stations to decrease, the multi-feeding short-circuit ratio to decrease, and the risk of simultaneous commutation failure of multiple direct current circuits to gradually increase, which makes the power grid face serious security and stability problems. In order to realize long-distance and large-capacity power transmission and multi-drop power supply and solve the problem of the decreasing multi-feeding short-circuit ratio at the receiving end, a hybrid cascaded UHV direct current transmission technology can be used, that is, a technical scheme in which a conventional direct current converter and multiple flexible direct current converters are connected in cascade. The technology combines the advantages of conventional direct current and flexible direct current, can effectively improve the stability of the receiving end alternating current power grid, has high reliability, flexible operation mode, and wide application prospect, and is a key technology for building a future energy internet.

[0003] The receiving end converter of the hybrid cascaded UHV direct current is generally connected to different alternating current buses of the same power grid, but the electrical distance between the alternating current buses is relatively short. When an alternating current system fault occurs, the voltage of the alternating current bus of each receiving end converter will drop, and then the output power of each flexible direct current converter is limited and the conventional direct current converter commutation failure will occur. Since the sending end cannot timely reduce the power, and the high-voltage end commutation failure will also cause the overcharge of the direct current, the power flowing into the flexible direct current unit on the direct current side will be greater than the power flowing out on the alternating current side, and the surplus power will continuously charge the sub-module capacitor of the flexible direct current valve, causing the module voltage to rise. If the module voltage rises too fast, the valve will be locked due to overvoltage, and finally the fault ride-through fails, and the flexible direct current of the hybrid cascaded system stops operating. In addition, when a single-phase grounding fault or the like occurs in the flexible direct current valve, a serious follow-up overvoltage is faced, which brings great harm to the safety of the equipment.

[0004] In order to suppress the overvoltage of the converter valve, a controllable self-restoration energy dissipation device is connected in parallel between the terminals of the flexible direct current valve. A part of the arrester valve is short-circuited quickly, and the fixed part of the arrester provides a discharge circuit, so as to limit the overvoltage of the VSC terminal. However, since the energy dissipation device adopts hundreds of columns of arrester in parallel, the manufacturing difficulty of the equipment is extremely great, and it is necessary to study a new control method to suppress the overvoltage of the flexible direct current valve, reduce the transient stress of the flexible direct current valve and the energy dissipation device, and improve the safety level of the equipment and the fault ride-through capability of the system. SUMMARY

[0005] To solve the above problems, the application aims to provide a pole control-valve control coordinated control method for overvoltage of a flexible DC converter valve in a hybrid cascade EHV DC system, which can reduce the overvoltage level of the flexible DC converter valve under AC system fault and valve side fault of a converter transformer, and avoid failure of fault ride-through or damage of equipment.

[0006] In the first aspect, the application provides a pole control-valve control coordinated control method for overvoltage of a flexible DC converter valve in a hybrid DC system, which comprises the following steps of:

[0007] A switch frequency dynamic adjustment voltage sharing strategy is designed in the valve control layer, and the switch frequency is dynamically adjusted according to the average module capacitor voltage of the bridge arm;

[0008] A valve control imbalance protection direct triggering energy dissipation device input strategy is designed, and when the valve control imbalance protection of any VSC converter valve in the hybrid cascade DC is actuated, a controllable self-recovery energy dissipation device is directly triggered and input;

[0009] A converter valve overvoltage current limiting control strategy is designed in the pole control layer, and when the capacitor voltage of any bridge arm module of the any VSC converter valve is higher than a set value, the power fed into the AC system by each converter is increased.

[0010] Further, the switch frequency is dynamically adjusted according to the average module capacitor voltage of the bridge arm, which comprises the following steps of:

[0011] When the average module capacitor voltage of the bridge arm is lower than a set value u cset1 , a lower switch frequency f1 is adopted; when the average module capacitor voltage of the bridge arm is higher than a set value u cset1 , a higher switch frequency f2 is adopted, and the high frequency operation is maintained for a certain time or the module voltage is restored to the set normal value, and then the switch frequency is adjusted back to the lower switch frequency f1, wherein f1 is below 150 Hz, and f2 is greater than 150 Hz.

[0012] Further, the switch frequency is adjusted by using a voltage sharing algorithm.

[0013] Further, the switch frequency is dynamically adjusted according to the average module capacitor voltage of the bridge arm, and the specific process is as follows:

[0014] a. Collect the capacitor voltages of each module of the bridge arm, and calculate the average module capacitor voltage u cave .

[0015] b. Determine whether u cave is greater than a set value u cset1 , if yes, go to step c, and if no, go to step d;

[0016] c. Make the switch frequency of the bridge arm be a higher switch frequency f2 by using a voltage sharing algorithm, and determine whether the frequency increasing time exceeds a preset time t setOr the bridge arm average module capacitor voltage drops to a safe value, then adjust the switching frequency back to a lower switching frequency f1;

[0017] d, the bridge arm switching frequency is the lower switching frequency f1 by the voltage equalization algorithm.

[0018] Further, the valve control unbalance protection direct trigger energy dissipation device input strategy is designed, including:

[0019] The converter bridge arm current is collected, and the unbalanced current i unbalance is calculated based on the converter bridge arm current.

[0020] Whether i unbalance is greater than the set value i setting ; If yes, the controllable self-recovery efficiency device trigger signal is sent out, and the pole operation is executed, otherwise continue to run.

[0021] Further, the unbalanced current i unbalance is calculated based on the converter bridge arm current.

[0022] i unbalance = |i pa +i pb +i pc -i na -i nb -i nc |;

[0023] In the formula, i pa , i pb , i pc are the real-time currents of the upper bridge arms of a, b and c phases respectively, i na , i nb , i nc are the real-time currents of the lower bridge arms of a, b and c phases respectively.

[0024] Further, the overvoltage current limiting control strategy of the converter valve is designed in the pole control layer, including:

[0025] The valve control of each flexible direct current converter judges whether the module capacitor voltage of the bridge arm reaches the set value u cset2 , and reports the signal of whether the bridge arm is overvoltage to the pole control. The pole control takes or as the enable signal of the overvoltage current limiting when the enable signal is 1, and sets the active power current reference value i dref to the maximum current I max , and the direction is to output the active power to the alternating current system. When the bridge arm module voltage recovers, the active power current reference value is restored to the original output of the outer ring.

[0026] In a second aspect, the application further provides a pole control-valve control coordinated control system for overvoltage of a flexible DC converter valve of a hybrid DC system, comprising:

[0027] The voltage equalization adjustment unit is configured to design a switching frequency dynamic adjustment voltage equalization strategy at the valve control layer, and dynamically adjust the switching frequency according to the average capacitor voltage of the bridge arm module;

[0028] The energy dissipation device input unit is configured to design a valve control imbalance protection direct triggering energy dissipation device input strategy, and directly trigger the input of the controllable self-recovery energy dissipation device when the valve control imbalance protection of any VSC converter valve in the hybrid cascade DC system is actuated.

[0029] The overvoltage current limiting control unit is configured to design an overvoltage current limiting control strategy of the converter valve at the pole control layer, and increase the power fed into the AC system by each converter when the capacitor voltage of any bridge arm module of the any VSC converter valve is higher than a set value.

[0030] In a third aspect, the application further provides an electronic device comprising computer program instructions, wherein the program instructions are executed by a processor to implement the pole control-valve control coordinated control method for overvoltage of a flexible DC converter valve of a hybrid DC system.

[0031] In a fourth aspect, the application further provides a computer readable storage medium having computer program instructions stored thereon, wherein the program instructions are executed by a processor to implement the pole control-valve control coordinated control method for overvoltage of a flexible DC converter valve of a hybrid DC system.

[0032] The application has the following characteristics: 1. The application can reduce the overvoltage level of the flexible DC converter valve through control at the system level and the device level, effectively reduce the overvoltage stress of the flexible valve by about 10% without adding additional equipment, and effectively reduce the risk of failure of fault ride-through or damage to the equipment, because the switching frequency dynamic adjustment voltage equalization strategy is designed at the valve control layer, the valve control imbalance protection direct triggering energy dissipation device input strategy is designed, and the overvoltage current limiting control strategy of the converter valve is designed at the pole control layer; 2. The application has engineering implementability, parameters are easy to set, and through dynamic input, both the overvoltage in the transient state is low and the system does not oscillate in the steady state. In summary, the application can be widely applied to pole control-valve control coordinated control for overvoltage of a flexible DC converter valve of a hybrid DC system. BRIEF DESCRIPTION OF DRAWINGS

[0033] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a description of preferred embodiments, and are not meant to limit the application. Throughout the drawings, the same reference numerals are used for the same elements. In the drawings:

[0034] Figure 1 Flow chart of valve control switch frequency dynamic adjustment strategy for the embodiment of the present application.

[0035] Figure 2 Flow chart of valve control unbalance protection trigger energy dissipation device putting strategy for the embodiment of the present application.

[0036] Figure 3 Converter valve overvoltage current limiting controller for the embodiment of the present application.

[0037] Figure 4 Mixed cascade UHVDC system topology structure diagram for the embodiment of the present application.

[0038] Figure 5 Electronic device structure schematic diagram for the embodiment of the present application. DETAILED DESCRIPTION

[0039] It should be understood that the terms used herein are for the purpose of describing particular example embodiments and are not intended to be limiting. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises," "comprising," "includes," "including," and the like are to be construed to be inclusive (i.e., to include both instances of open- and closed-ended conditions) unless otherwise indicated. The methods described herein are not to be construed as requiring their steps to be performed in the particular order described or illustrated unless otherwise explicitly indicated. Additional or alternative steps can also be utilized.

[0040] For ease of description, spatial relative terms can be used herein to describe the relationship of one element or feature to another element or feature as shown in the figures, such as "inner," "outer," "inward," "outward," "lower," "upper," etc. Such spatial relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures.

[0041] To suppress overvoltage in flexible DC converter valves, reduce transient stress on the flexible DC converter valves and energy dissipation devices, and improve equipment safety and system fault ride-through capability, this invention provides a pole control-valve control coordinated control method, system, equipment, and medium for overvoltage control of flexible DC converter valves in hybrid DC systems. The method includes: designing a dynamic switching frequency adjustment and voltage equalization strategy at the valve control layer, dynamically adjusting the switching frequency based on the average module capacitor voltage of the bridge arm; designing a valve control imbalance protection direct triggering energy dissipation device activation strategy, directly triggering the activation of a controllable self-recovering energy dissipation device when the valve control imbalance protection of any VSC converter valve in the hybrid cascaded DC system is activated; and designing a converter valve overvoltage current limiting control strategy at the pole control layer, increasing the power fed into the AC system by each converter when the capacitor voltage of any bridge arm module of any VSC converter valve exceeds a set value.

[0042] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0043] Example 1: The pole control-valve control coordinated control method for overvoltage of flexible DC converter valve in a hybrid cascaded ultra-high voltage DC system provided in this example includes:

[0044] S1. Design a switching frequency dynamic adjustment module voltage equalization strategy in the valve control layer. The switching frequency is dynamically adjusted according to the average module capacitor voltage of the bridge arm, thereby reducing the voltage of a single module under the overall overvoltage of the converter valve.

[0045] In this embodiment, when the average module capacitor voltage of the bridge arm is lower than a certain value u cset1 When a lower switching frequency f1 is used, typically below 150Hz; when the average module capacitor voltage of the bridge arm is higher than a set value u cset1 When the overall bridge arm is overvoltage, a higher switching frequency f2 is used, generally greater than 150Hz. By increasing the switching frequency when the bridge arm is overvoltaged, the unevenness between modules is reduced, thereby reducing the overvoltage of individual modules. The high frequency operation is maintained for a certain period of time or until the module voltage returns to the normal value. Then the switching frequency is adjusted back to the original lower switching frequency f1.

[0046] Furthermore, the switching frequency can be adjusted according to the voltage equalization algorithm used, such as increasing the holding factor or reducing the allowable voltage deviation between modules, etc., without limitation here.

[0047] Furthermore, such as Figure 1 As shown, the specific process of dynamically adjusting the switching frequency of a bridge arm based on the average module capacitor voltage of the bridge arm includes:

[0048] S11, collect the capacitor voltage of each module of the bridge arm, and calculate the average value of the capacitor voltage of the module u ci is the real-time capacitor voltage of the i-th module, and n is the number of modules;

[0049] S12, judge whether u cave is greater than a set value u cset1 If yes, go to step S13, and if no, go to step S14;

[0050] S13, by adjusting the voltage equalization retention factor, the allowed voltage deviation between modules and other voltage equalization algorithms, the switching frequency of the bridge arm is the higher switching frequency f2, and it is determined that the frequency increasing time exceeds the preset time t set , or the average module capacitor voltage of the bridge arm drops to a safety value, then the switching frequency is adjusted back to the lower switching frequency f1.

[0051] S14, by adjusting the voltage equalization retention factor, the allowed voltage deviation between modules and other voltage equalization algorithms, the switching frequency of the bridge arm is the lower switching frequency f1.

[0052] S2, design a valve control unbalance protection direct trigger energy dissipation device input strategy, when the valve control unbalance protection of any VSC valve in the hybrid cascade DC acts, directly trigger the input of the controllable self-recovery energy dissipation device without waiting for the overvoltage of the bridge arm, so as to realize the rapid input of the energy dissipation device and more quickly suppress the overvoltage of the valve;

[0053] In this embodiment, the method of triggering the energy dissipation device input by the valve control unbalance protection is: the sum of the currents of the three upper bridge arms minus the sum of the currents of the three lower bridge arms to form an unbalance current, when the unbalance current is greater than a constant I set , the valve control unbalance protection acts after a microsecond delay; after the valve control unbalance protection acts, the energy dissipation device is directly triggered to input through the communication channel controlled by the valve control and the energy dissipation device body, and at the same time, the input signal of the energy dissipation device is sent through the standby channel of the valve control→pole control→energy dissipation device, when the energy dissipation device receives the closing instruction, the overvoltage is suppressed by short-circuiting the controllable part through the fast switch. At the same time, after the unbalance protection acts, the pole control executes the pole stop operation.

[0054] Further, as Figure 2 shown, the valve control unbalance protection direct trigger energy dissipation device input strategy includes:

[0055] S21, collect the currents of the six bridge arms of the converter, and calculate the unbalance current i unbalance based on the bridge arm current of the converter:

[0056] i unbalance = |i pa +i pb +i pc-i na -i nb -i nc |;

[0057] wherein i pa , i pb , i pc are real-time currents of upper bridge arms of phases a, b and c respectively, i na , i nb , i nc are real-time currents of lower bridge arms of phases a, b and c respectively.

[0058] S22, judging whether i unbalance is greater than a set value i setting ; if yes, a controllable self-recovery performance device trigger signal is sent out, and a pole control operation is executed, otherwise, the operation continues.

[0059] S3, a converter valve overvoltage current limiting control strategy is designed in the pole control layer, when the capacitor voltage of any bridge arm module of any VSC converter valve is higher than a certain value u cset2 , the power fed into the AC system by each converter is rapidly increased to suppress the module overvoltage caused by power surplus by rapidly increasing the power absorbed on the AC side.

[0060] As shown in Figure 3 , the converter valve overvoltage current limiting control strategy: the valve control of each flexible DC converter judges whether the capacitor voltage of any bridge arm module (for example, VSC1 overvoltage, VSC2 overvoltage, VSC3 overvoltage) reaches a certain value u cset2 , then the signal of whether any bridge arm is overvoltage is reported to the pole control, the bridge arm overvoltage signal returned by each converter is taken or as an enable signal of overvoltage current limiting sent to the inner loop input of the controller, when the enable signal is 1, the active power current reference value i dref is set to the maximum current I max , and the direction is to output active power to the AC system. When the bridge arm module voltage is restored, the active power current reference value is restored to the original output of the outer loop.

[0061] In this embodiment, the method of rapidly increasing the power fed into the AC system by each converter is: the active current reference instruction in the dq decoupling control of each flexible DC converter is directly adjusted to the maximum current limit, and the direction is to output active power to the system, and when the module voltage drops to within the safe range, the active current reference instruction is restored to the output value of the outer loop controller.

[0062] The application of the pole control-valve control coordinated control method of the overvoltage of the flexible DC converter valve of the hybrid cascade UHV DC system of the application will be described in detail through specific embodiments.

[0063] As shown in Figure 4As shown, the sending end of the hybrid cascaded UHVDC transmission system adopts a conventional UHVDC topology, and each pole is composed of two twelve-pulse conventional DC converters in cascade. The receiving end adopts a hybrid cascaded UHVDC topology, and each pole is composed of a high-voltage (i.e. 800 kV-400 kV) twelve-pulse conventional DC converter and a plurality of (three in the figure) parallel flexible DC converters in the low-voltage (400 kV-neutral line) end. The flexible DC converter adopts a half-bridge modular multilevel converter. The conventional DC converter and each flexible DC converter in the receiving end are fed into different AC buses.

[0064] The specific implementation process of the pole control-valve control coordinated control method for overvoltage of the flexible DC converter valve of the hybrid cascaded UHVDC system is as follows:

[0065] 1. Valve control layer designs a switch frequency dynamic adjustment module voltage balancing strategy

[0066] Specifically, the valve control layer monitors the average voltage of each module of the bridge arm in real time. When the average module capacitor voltage of the bridge arm is lower than a predetermined value u cset1 , a larger sorting retention factor is set in the sorting voltage balancing or a larger voltage deviation between modules in the same bridge arm is allowed, so as to maintain a lower switch frequency f1 of the bridge arm to reduce the loss of the converter valve. When the average module capacitor voltage of the bridge arm is higher than a predetermined value u cset1 , the sorting retention factor or the voltage deviation between modules in the same bridge arm is immediately adjusted, so as to temporarily increase the switch frequency to a higher switch frequency f2. When the frequency increasing time exceeds a preset time t set or the average module capacitor voltage of the bridge arm decreases to a safety value, the switch frequency is adjusted back to the lower switch frequency f1.

[0067] 2. Valve control imbalance protection directly triggers the energy dissipation device strategy

[0068] Specifically, the valve control layer collects the current values of the six bridge arms in real time, and calculates the unbalanced current of the converter valve according to the sum of the upper bridge arm currents minus the sum of the lower bridge arm currents. When the unbalanced current reaches a predetermined value, the valve control layer outputs after a microsecond delay. After the valve control imbalance protection acts, a command for requesting the energy dissipation device to be put into operation is directly sent to the body control of the energy dissipation device. One channel is directly sent from the valve control of the flexible DC to the body control of the energy dissipation device, and the other channel is first uploaded from the valve control of the flexible DC to the pole control and then sent from the pole control to the body control of the energy dissipation device. The two channels are mutually redundant, so that the energy dissipation device can still be triggered when any channel is abnormal. When the energy dissipation device receives the closing command, the overvoltage is suppressed by short-circuiting the controllable part through a fast switch. At the same time, the pole control layer executes the pole stopping operation after the imbalance protection acts.

[0069] 3. Overvoltage current limiting control action of the converter valve

[0070] Specifically, the valve control determines whether the module capacitor voltage of the bridge arm of each flexible direct current (HVDC) converter reaches a constant value u cset2 Then, the signal of whether the bridge arm is overvoltage is reported to the pole control, and the pole control takes or of the overvoltage signals of the bridge arms returned by each converter as an enable signal of overvoltage current limiting. When the enable signal is 1, the active power current reference value i dref is set to the maximum current I max , and the direction is to output active power to the alternating current system. When the bridge arm module voltage is restored, the active power current reference value is restored to the output of the original outer ring.

[0071] Embodiment two: the pole control-valve control coordinated control method provided in the above embodiment one for suppressing overvoltage of the flexible HVDC converter valve of the hybrid cascade HVDC system. Correspondingly, the present embodiment provides a pole control-valve control coordinated control system for suppressing overvoltage of the flexible HVDC converter valve of the hybrid cascade HVDC system. The system provided in the present embodiment can implement the pole control-valve control coordinated control method for suppressing overvoltage of the flexible HVDC converter valve of the hybrid cascade HVDC system provided in the embodiment one. The system can be implemented by software, hardware or a combination of software and hardware. For the convenience of description, the system in the present embodiment is described as various units. Of course, the functions of the units can be implemented in the same or multiple software and / or hardware. For example, the system can include integrated or separate functional modules or functional units to perform the corresponding steps in the method of the embodiment one. Since the system in the present embodiment is basically similar to the method embodiment, the description process of the present embodiment is relatively simple, and the related parts can be referred to the part of the description of the embodiment one. The embodiment of the pole control-valve control coordinated control system for suppressing overvoltage of the flexible HVDC converter valve of the hybrid cascade HVDC system provided in the present application is only illustrative.

[0072] Specifically, the pole control-valve control coordinated control system for overvoltage of the flexible HVDC converter valve of the hybrid HVDC system provided in the present embodiment includes:

[0073] The voltage adjustment unit is configured to design a switch frequency dynamic adjustment voltage strategy at the valve control layer, and dynamically adjust the switch frequency according to the average module capacitor voltage of the bridge arm;

[0074] The energy dissipation device input unit is configured to design a valve control imbalance protection direct trigger energy dissipation device input strategy. When the valve control imbalance protection of any VSC converter valve in the hybrid cascade HVDC system is actuated, the controllable self-restoration energy dissipation device is directly triggered.

[0075] The overvoltage current limiting control unit is configured to design an overvoltage current limiting control strategy of the converter valve at the pole control layer. When the module capacitor voltage of any bridge arm of the any VSC converter valve is higher than a set value, the power fed into the alternating current system by each converter is increased.

[0076] Embodiment three: the electronic device corresponding to the pole control-valve control coordination control method for inhibiting overvoltage of the flexible DC converter valve of the hybrid cascade UHVDC system provided in embodiment one, the electronic device can be an electronic device for a client, such as a mobile phone, a notebook computer, a tablet computer, a desktop computer, etc., to execute the method of embodiment one.

[0077] As shown in Figure 5 The electronic device includes a processor, a memory, a communication interface and a bus, the processor, the memory and the communication interface are connected through the bus to complete the communication among each other. The bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Component (EISA) bus, etc. The memory stores a computer program executable on the processor, and the processor executes the computer program to execute the pole control-valve control coordination control method for inhibiting overvoltage of the flexible DC converter valve of the hybrid cascade UHVDC system provided in embodiment one. Those skilled in the art can understand that Figure 5 The structure shown in

[0078] In some implementations, the logical instructions in the memory described above can be implemented in the form of a software function unit and sold or used as an independent product, which can be stored in a computer readable storage medium. Based on such understanding, the technical solutions of the present application essentially or the part that contributes to the prior art or part of the technical solutions can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a plurality of instructions to make a computer device (which can be a personal computer, a server, or a network device, etc.) execute all or part of the steps of the method described in various embodiments of the present application. The foregoing storage medium includes a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), an optical disc and various program code storage media.

[0079] In other implementations, the processor can be a central processing unit (CPU), a digital signal processor (DSP) and various types of general-purpose processors, which are not limited here.

[0080] In an embodiment, the method of inhibiting overvoltage of the flexible DC converter valve of the hybrid cascaded UHVDC system can be embodied in a computer program product, which can include a computer-readable storage medium having stored thereon instructions that, when executed by a computer, cause the computer to carry out the method of inhibiting overvoltage of the flexible DC converter valve of the hybrid cascaded UHVDC system.

[0081] The computer-readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer-readable storage medium can be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination thereof.

[0082] The various embodiments described in the specification can be described in progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the difference from other embodiments. In particular, the system embodiments are described in a relatively simple manner because they are basically similar to the method embodiments. In the description of the specification, the description of the terms "one embodiment", "some implementations", and the like 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 embodiments described in the specification. The illustrative description of the above terms in the specification does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0083] The present application is described with reference to flowcharts and / or block diagrams according to the method, device (system), and computer program product of the embodiments. It should be understood that each flow and / or block in the flowchart and / or block diagram can be implemented by computer program instructions. These computer program instructions can be provided to a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the computer or other programmable data processing device produce a device that implements the functions specified in the flowchart and / or block diagram block. Figure 1 The function of the device specified in one flow or multiple flows and / or blocks Figure 1 The function of the device specified in one flow or multiple flows and / or blocks

[0084] These computer program instructions can also be stored in a computer readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instructions which implement the flow Figure 1 of the flow or flows and / or blocks Figure 1 of the block or blocks specified in the flow.

[0085] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the flow Figure 1 of the flow or flows and / or blocks Figure 1 of the block or blocks specified in the flow.

[0086] Finally, it should be noted that the above-mentioned embodiments are merely used to illustrate the technical solutions of the present application, rather than limit the present application; even though the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some of the technical features can be replaced by equivalent features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A pole control-valve control coordinated control method for overvoltage of a flexible direct current system flexible direct current converter valve, characterized in that, Comprise: Designing a switching frequency dynamic adjustment voltage sharing strategy at the valve control layer, dynamically adjusting the switching frequency according to the average module capacitor voltage of the bridge arm; Dynamically adjusting the switching frequency according to the average module capacitor voltage of the bridge arm, comprising: When the bridge arm average module capacitor voltage is lower than the set value u cset1 Lower switching frequency is adopted f 1; When the bridge arm average module capacitor voltage is higher than the set value u cset1 Higher switching frequency is adopted f 2, maintain high frequency operation for a certain time or wait for the module voltage to recover to the set normal value, then adjust the switching frequency back to the lower switching frequency f 1, wherein f 1 is 150 Hz or less, f 2 is greater than 150 Hz; the switching frequency is adjusted using a voltage equalization algorithm; The specific process of dynamically adjusting the switching frequency according to the average module capacitor voltage of the bridge arm is: a、collecting the capacitor voltage of each module of the bridge arm, calculating the average value of the capacitor voltage of the module ; b. judging whether greater than a set value u cset1 if yes, go to step c, if no, go to step d c. The bridge arm switch frequency is made to be a higher switch frequency through the voltage equalization algorithm f 2. Determine if the frequency increase time exceeds a preset time t set Or the bridge arm average module capacitor voltage drops to a safe value, then adjust the switch frequency back to a lower switch frequency f 1; d. The bridge arm switching frequency is made lower by the equalization algorithm f 1. Designing a valve control imbalance protection direct trigger energy dissipation device input strategy, when the valve control imbalance protection of any VSC converter valve in the hybrid cascaded DC acts, directly triggering the input of the controllable self-restoration energy dissipation device; wherein: The converter bridge arm current is acquired, and the unbalanced current i is calculated based on the converter bridge arm current unbalance : Judge i unbalance Whether greater than the set value i setting If yes, send controllable self-restoration energy dissipation device trigger signal, and execute stop pole operation, otherwise continue running; Designing a converter valve overvoltage current limiting control strategy at the pole control layer, when the capacitor voltage of any bridge arm module of the VSC converter valve is higher than the set value, increasing the power fed into the AC system by each converter.

2. The pole control-valve control coordinated control method for HVDC system HVDC valve overvoltage according to claim 1, characterized in that, Based on the inverter bridge arm current to calculate the unbalanced current i unbalance This is achieved by the following equation: ； In the formula, i pa , i pb , i pc These are the real-time currents of the upper bridge arms for phases a, b, and c, respectively. i na , i nb , i nc These are the real-time currents of the lower bridge arms for phases a, b, and c, respectively.

3. The pole control-valve control coordinated control method for HVDC system HVDC valve overvoltage according to claim 1, characterized in that, Designing a converter valve overvoltage current limiting control strategy at the pole control layer, comprising: The valve control of each line-commutated converter determines whether the module capacitor voltage of the bridge arm reaches a certain value u cset2 The signal of whether the bridge arm is overvoltage is reported to the pole control, and the pole control takes or of the bridge arm overvoltage signals returned by each converter as an enable signal of overvoltage current limiting. When the enable signal is 1, the active power current reference value i dref is set to the maximum current I max , and the direction is to output active power to the alternating current system. When the bridge arm module voltage is restored, the active power current reference value is restored to the original output of the outer ring.

4. A system for implementing the pole-control-valve-control coordinated control method of overvoltage of a flexible direct current system converter valve according to any one of claims 1-3, characterized in that, Comprise: The voltage sharing adjustment unit is configured to design a switching frequency dynamic adjustment voltage sharing strategy at the valve control layer, and dynamically adjust the switching frequency according to the average module capacitor voltage of the bridge arm; The energy dissipation device input unit is configured to design a valve control imbalance protection direct trigger energy dissipation device input strategy, when the valve control imbalance protection of any VSC converter valve in the hybrid cascaded DC acts, directly triggering the input of the controllable self-restoration energy dissipation device; The overvoltage current limiting control unit is configured to design a converter valve overvoltage current limiting control strategy at the pole control layer, when the capacitor voltage of any bridge arm module of the VSC converter valve is higher than the set value, increasing the power fed into the AC system by each converter.

5. An electronic device, comprising: The computer readable storage medium stores computer program instructions, wherein the program instructions are executed by the processor to implement the pole control-valve control coordinated control method for overvoltage of the flexible DC converter valve of the hybrid DC system according to any one of claims 1-3.

6. A computer readable storage medium characterized by The computer readable storage medium stores computer program instructions, wherein the program instructions are executed by the processor to implement the pole control-valve control coordinated control method for overvoltage of the flexible DC converter valve of the hybrid DC system according to any one of claims 1-3.

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