Optimization control method, device and equipment for switching operation modes of DC island system

Abstract

The present application relates to an optimization control method, device and equipment for switching the operation mode of a DC island system. The method includes obtaining the operation mode type and system frequency difference of the DC island system; if the operation mode type is an isolated grid mode in the island mode, a shielding strategy is used to prevent the DC island system from entering the isolated grid mode, so that the DC island system always maintains the operation in the island mode; the shielding strategy includes adjusting the upper limit value of the frequency dead zone in the isolated grid mode or setting the enable signal of the isolated grid mode to zero. The optimization control method for switching the operation mode of a DC island system adopts a shielding strategy to prevent the DC island system from entering the isolated grid mode based on the operation mode type of the DC island system being the isolated grid mode operation in the island mode, so as to avoid the mutual influence of the dual control of the island mode control and the isolated grid mode control, which leads to the problem of the DC island system being unstable.

Description

Technical Field

[0001] The present application relates to the technical field of island control of a DC island system, and in particular to an optimization control method, device and equipment for switching operation modes of a DC island system. Background Art

[0002] In general, the frequency regulation strategy in the DC island mode of the DC transmission system generally adopts the method of coordinating the DC frequency control FLC and the primary frequency regulation of the unit. Because the regulation capability of the DC FLC is much faster than the primary frequency regulation capability of the unit, when the FLC frequency control dead zone is smaller than the primary frequency regulation of the unit, it can ensure that the system frequency can be quickly stabilized within the DC frequency limit control dead zone during the switching process between the interconnected mode and the island mode of the DC transmission system.

[0003] The existing DC transmission system has the situation that a small nearby grid is connected to DC in the island mode. In this case, the frequency fluctuation of the frequency regulation strategy during the conversion process of the interconnected island may exceed ±0.5Hz, and the isolated grid mode is entered first, limiting the dead zone of the primary frequency regulation to 0. When the DC transmission system enters the isolated grid mode in the island mode, the DC transmission system will initially stabilize at 49.9Hz / 50.1Hz due to the rapid action of the DC FLC, and the dead zone of the primary frequency regulation is limited to 0 by the isolated grid mode; the power regulation amount generated by the FLC regulation will slowly retreat, and the unit will slowly increase the power through the primary frequency regulation, and the increase speed depends on the PID parameters of the primary frequency regulation of the unit. After a considerable period of time, the frequency of the DC transmission system in the DC island mode will eventually stabilize at 50Hz, meeting the requirement that the frequency dead zone is 0, but in this case the frequency regulation strategy does not meet the requirement of fast control of frequency stability when switching between the DC island mode, interconnected mode, and arc grid mode. This frequency regulation strategy may cause additional oscillation problems in the DC transmission system during the slow power regulation process of the unit in the isolated grid mode, posing a threat to the stability of the DC transmission system. Summary of the invention

[0004] The embodiments of the present application provide an optimized control method, device and equipment for switching the operating modes of a DC island system, which is used to solve the technical problem that the existing frequency modulation strategy does not meet the requirements of fast control frequency stability in conversion between island mode, networking mode and arc network mode, and there are additional oscillations, which pose a threat to the stability of the DC transmission system.

[0005] In order to achieve the above objectives, the embodiments of the present application provide the following technical solutions:

[0006] On the one hand, an optimization control method for switching operation modes of a DC island system is provided, comprising the following steps:

[0007] Obtain the operating mode type and system frequency difference of the DC island system;

[0008] If the operation mode type is an isolated grid mode in an island mode, a shielding strategy is adopted to prevent the DC island system from entering the isolated grid mode, so that the DC island system always maintains the operation in the island mode;

[0009] The shielding strategy includes adjusting the upper limit value of the frequency dead zone in the isolated network mode or setting the enable signal of the isolated network mode to zero.

[0010] Preferably, if the shielding strategy is to adjust the upper limit value of the frequency dead zone in the isolated network mode, the content of preventing the DC island system from entering the isolated network mode includes:

[0011] Obtaining a frequency dead zone adjustment value after adjusting the upper limit value of the frequency dead zone in the isolated network mode;

[0012] If the system frequency difference is not greater than the frequency dead zone adjustment value and the system frequency difference is not less than the negative frequency dead zone adjustment value, adjusting the enable signal of the isolated network mode to 0;

[0013] If the system frequency difference is greater than the frequency dead zone adjustment value or the system frequency difference is less than the negative frequency dead zone adjustment value, the enable signal of the isolated network mode is adjusted to 1, and the frequency dead zone adjustment value is increased until the system frequency difference is not greater than the frequency dead zone adjustment value and the system frequency difference is not less than the negative frequency dead zone adjustment value.

[0014] Preferably, the frequency dead zone adjustment value is 50 Hz.

[0015] Preferably, the content of obtaining the operation mode type of the DC island system includes:

[0016] Obtaining the actual frequency of the DC island system and the disconnection state of the AC line;

[0017] Determining, according to the disconnection state, whether the DC island system is operating in a networking mode or in the island mode;

[0018] When the DC island system is in the networking mode or the island mode, the actual frequency is compared with the frequency threshold to determine whether the operation mode type of the DC island system is the isolated network mode in the networking mode or the operation mode type of the DC island system is the isolated network mode in the island mode.

[0019] Preferably, comparing the actual frequency with the frequency threshold to determine whether the operating mode type of the DC island system is the isolated network mode in the networking mode or the operating mode type of the DC island system is the isolated network mode in the island mode includes: if the actual frequency is not within the frequency threshold range, then the operating mode type of the DC island system is the isolated network mode in the networking mode or the operating mode type of the DC island system is the isolated network mode in the island mode.

[0020] Preferably, the optimization control method for switching the operating mode of the DC island system includes: if the operating mode type of the DC island system is the isolated network mode under the networking mode, the frequency dead zone value in the isolated network mode is not adjusted; if the operating mode type of the DC island system is the isolated network mode under the island mode, a shielding strategy is adopted to prevent the DC island system from entering the isolated network mode.

[0021] In yet another aspect, an optimization control device for switching operation modes of a DC island system is provided, comprising a data acquisition module and an optimization control module;

[0022] The data acquisition module is used to obtain the operation mode type and system frequency difference of the DC island system;

[0023] The optimization control module is used for, if the operation mode type is an isolated grid mode in an island mode, adopting a shielding strategy to prevent the DC island system from entering the isolated grid mode, so that the DC island system always maintains the island mode operation;

[0024] The shielding strategy includes adjusting the upper limit value of the frequency dead zone in the isolated network mode or setting the enable signal of the isolated network mode to zero.

[0025] Preferably, the optimization control module includes an adjustment parameter acquisition submodule, an optimization control submodule and an adjustment submodule;

[0026] The adjustment parameter acquisition submodule is used to obtain the frequency dead zone adjustment value after adjusting the upper limit value of the frequency dead zone in the isolated network mode;

[0027] The optimization control submodule is used to adjust the enable signal of the isolated network mode to 0 according to the system frequency difference being not greater than the frequency dead zone adjustment value and the system frequency difference being not less than the negative frequency dead zone adjustment value;

[0028] The adjustment submodule is used to adjust the enable signal of the isolated network mode to 1, and increase the frequency dead zone adjustment value according to the system frequency difference being greater than the frequency dead zone adjustment value or the system frequency difference being less than the negative frequency dead zone adjustment value, until the system frequency difference is not greater than the frequency dead zone adjustment value and the system frequency difference is not less than the negative frequency dead zone adjustment value.

[0029] Preferably, the data acquisition module includes a data acquisition submodule, a first mode determination submodule and a second mode determination submodule;

[0030] The data acquisition submodule is used to obtain the actual frequency of the DC island system and the disconnection status of the AC line;

[0031] The first mode determination submodule is used to determine whether the DC island system is operating in the networking mode or the island mode according to the disconnection state;

[0032] The second mode determination submodule is used to compare the actual frequency with the frequency threshold when the DC island system is in the networking mode or the island mode, and determine that the operating mode type of the DC island system is the isolated network mode in the networking mode or the operating mode type of the DC island system is the isolated network mode in the island mode.

[0033] Preferably, the optimization control submodule is also used for not adjusting the frequency dead zone value in the isolated network mode according to the operating mode type of the DC island system being the isolated network mode under the networking mode; and for adopting a shielding strategy to prevent the DC island system from entering the isolated network mode according to the operating mode type of the DC island system being the isolated network mode under the island mode.

[0034] In another aspect, a terminal device is provided, comprising a processor and a memory;

[0035] The memory is used to store program codes and transmit the program codes to the processor;

[0036] The processor is used to execute the above-mentioned optimization control method for switching the operation mode of the DC island system according to the instructions in the program code.

[0037] The optimization control method, device and equipment for switching the operation mode of the DC island system, the method includes obtaining the operation mode type and system frequency difference of the DC island system; if the operation mode type is the isolated network mode in the island mode, a shielding strategy is adopted to prevent the DC island system from entering the isolated network mode, so that the DC island system always maintains the operation in the island mode; wherein the shielding strategy includes adjusting the upper limit value of the frequency dead zone in the isolated network mode or setting the enable signal of the isolated network mode to zero. It can be seen from the above technical scheme that the embodiment of the present application has the following advantages: the optimization control method for switching the operation mode of the DC island system adopts a shielding strategy to prevent the DC island system from entering the isolated network mode based on the operation mode type of the DC island system being the isolated network mode in the island mode, so as to avoid the mutual influence of the dual control of the isolated mode control and the isolated network mode control, resulting in the problem of the DC island system being destroyed in stability; it solves the technical problem that the existing frequency modulation strategy does not meet the requirements of fast control frequency stability in the conversion between the island mode, the networking mode and the arc network mode, and there are additional oscillations, which threatens the stability of the DC transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0039] Figure 1 The topological structure diagram of the interconnected mode and the island mode of the existing DC transmission system;

[0040] Figure 2 The topological structure diagram of the existing DC transmission system including the island mode of the internal isolated power grid and the external large power grid;

[0041] Figure 3 A topological structure diagram of an existing DC transmission system including an island mode with an internal isolated power grid;

[0042] Figure 4 The topological structure diagram of the isolated grid mode in which the existing DC transmission system is disconnected and the nearby large power grid is disconnected;

[0043] Figure 5 A control logic diagram for switching the operation mode of an existing DC transmission system through a speed regulator;

[0044] Figure 6 A flowchart of the steps of the optimization control method for switching the operation mode of the DC island system according to the embodiment of the present application;

[0045] Figure 7It is an optimization control logic diagram of the optimization control method for switching the operation mode of the DC island system described in the embodiment of the present application;

[0046] Figure 8 An optimized control logic diagram of an optimized control method for switching operation modes of a DC island system according to another embodiment of the present application;

[0047] Fig. 9 A schematic diagram of a framework of an optimization control device for switching operation modes of a DC island system according to an embodiment of the present application;

[0048] Fig.10 A schematic diagram of a terminal device described in an embodiment of the present application. DETAILED DESCRIPTION

[0049] In order to make the purpose, features, and advantages of the invention of this application more obvious and easy to understand, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the embodiments described below are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0050] In the description of the embodiments of the present application, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0051] In the embodiments of the present application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0052] Patent terms for this application:

[0053] DC island system: A relatively independent "island" system is formed at the sending end of the DC transmission system and several power plants, also known as a DC transmission and sending-end power station system. The DC island system is not connected to the AC system of the large power grid, and the power is directly sent to the receiving end through the DC transmission system. The use of the DC island system operation mode can effectively reduce the impact of DC system failures on the main grid and improve the safety and stability of the power grid.

[0054] The DC changes from grid-connected to island mode when the connection line between the DC and the main grid is disconnected and the DC enters the island operation mode.

[0055] Frequency limit control (FLC) is a kind of additional control for DC transmission system. It uses the fast controllability of DC transmission system power to adjust the power transmitted by DC system according to the change of AC system frequency at the DC sending end (or receiving end), and keeps the AC system frequency at the sending end (or receiving end) at the rated value or within the set dead zone. In particular, when DC is in an island operation state or the sending end (or receiving end) regional power grid is disconnected from the system, the frequency control dead zone can be reduced by manually inputting control signals, so that the DC system can perform frequency control. As an additional control, the FLC control function controls the DC transmission system together with the main control system of the DC transmission system.

[0056] In the embodiment of the present application, there are two operating modes of the DC transmission system, one is the common interconnected operation mode, and the other is the island operation mode. The interconnected operation mode (also called the interconnected mode) refers to the operation mode in which the converter stations on both sides maintain interconnected operation with the main grid, such as Figure 1 The external power grid shown is connected to the main grid through a tie line. The island operation mode (also called island mode) refers to the operation mode in which the converter station and the adjacent power stations and lines form an independent small system and are disconnected from the main grid. Figure 1 The operation mode shown is to disconnect the external power grid from the main grid by disconnecting the tie line, such as Figure 2 The DC transmission system with disconnected tie lines shown in the figure contains an island mode of an internal isolated power grid and an external large power grid, such as Figure 3 The DC transmission system shown includes an island mode with an internal isolated grid.

[0057] DC transmission has been widely used in the implementation of strategies such as economical and efficient large-capacity and long-distance power transmission technology. In particular, with the construction of a new batch of giant energy bases, UHV DC transmission systems with higher voltage levels and larger capacities have gradually emerged. These newly built energy bases are generally located in remote areas. Several sending-end power stations are connected to the UHV DC converter station through the supporting AC transmission system to form a DC sending-end network, which often forms a weak connection with the main grid. In the planning of DC transmission projects, the power transmission mode of the UHV DC sending end using an island operation mode is generally considered. In the operation of the power grid, when there is a fault in the DC sending-end system and the AC connecting line N-1 / N-2 of the main grid, the DC sending-end network is forced to lose connection with the main grid, forming an island operation mode.

[0058] Most existing DC transmission systems are connected to both external large power networks and isolated power grids in nearby areas through tie lines at the sending end. Often, when the tie lines of the external large power network are disconnected, the internal isolated power grid is operated, forming an isolated grid operation mode, also known as island mode.

[0059] like Figure 4 As shown in the figure, the operation mode with isolated load (also known as isolated grid mode) is also called the "large machine and small grid" operation condition. At this time, the proportion of hydropower units in the power grid system is relatively large. Any slight change in the unit load will cause fluctuations in the power grid frequency. Therefore, the control requirements for the unit speed regulation system of the power grid are relatively high. In this isolated grid mode, the speed regulator of the frequency regulation strategy also needs to set separate adjustment parameters, and the identification and parameter processing of the large machine and small grid operation mode are required.

[0060] The content of the FM strategy is:

[0061] At present, the commonly used unit mode identification method is mainly based on frequency deviation, and active power is generally added as an auxiliary judgment. The identification logic of the unit's grid-connected mode and no-load mode is as follows: when the unit is in grid-connected mode, but the frequency detection of the DC transmission system exceeds 50±0.5Hz, and the active power of the unit is greater than 10% of the rated power, it will delay for 1 second and switch the grid-connected mode to the isolated mode through the speed governor; when the frequency of the DC transmission system exceeds 50±0.5Hz, the active power of the unit is less than 10% of the rated power, it will delay for 1 second and switch the grid-connected mode to the no-load mode through the speed governor.

[0062] In the DC transmission system, the switch between the island mode and the interconnection mode is usually determined by the opening of the tie line switch. In the interconnection mode, the unit adjusts the frequency through the primary frequency regulation of the speed regulator, and the dead zone of the speed regulator control is generally 0.05Hz. In the island mode, the unit also adjusts the frequency through the primary frequency regulation of the unit, and the dead zone of the speed regulator control is generally 0.15Hz.

[0063] The judgment logic for entering the isolated grid mode is that when the frequency fluctuation of the DC transmission system exceeds ±0.5Hz, it automatically enters the isolated grid mode and remains unchanged. The isolated grid mode is a special frequency mode, and its frequency dead zone is generally set to 0.

[0064] At present, the operation modes of the DC transmission system include no-load mode, networking mode, isolated mode and island mode. No-load mode refers to the state where the generator establishes voltage, the circuit breaker between the generator and the machine end is not closed, the generator is not connected to the grid, and it is not transmitting power to the outside. Load mode refers to the state where the generator establishes voltage, the circuit breaker between the generator and the machine end is closed, and power can be transmitted to the outside. Networking mode refers to the state where the generator establishes voltage, the circuit breaker between the generator and the machine end is closed, and the generator is connected to the main grid and can generate power to the outside. Isolated mode refers to the state where the generator establishes voltage, the circuit breaker between the generator and the machine end is closed, the generator is only connected to a nearby small grid, and only transmits power to the nearby small grid. Island mode refers to the state where the generator establishes voltage, the circuit breaker between the generator and the machine end is closed, but the generator only transmits power through the DC transmission channel connected to the machine end.

[0065] Figure 5 This is the control logic diagram of the existing DC transmission system switching the operating mode through the speed regulator. Figure 5 ① is the no-load and load logic selection module; ② is the no-load and load switch judgment module; ③ is the networking and island mode judgment module; ④ is the networking and island logic selection module; ⑤ is the isolated network judgment logic module; ⑥ is the logic judgment for entering the isolated network in the networking mode; ⑦ is the logic judgment for entering the isolated network in the island mode; ⑧ is the PID output logic for selecting the isolated network, island and no-load signals; ⑨ is the execution structure, relay and turbine part of the speed regulator.

[0066] In this embodiment, if Figure 5 As shown in FIG. 1 , the control logic of the existing DC transmission system switching the operation mode through the speed regulator includes:

[0067] First, the system frequency difference Δf is defined by the difference between the control target frequency cf and the actual frequency f of the DC transmission system, and the system frequency difference Δf is used as the input of all subsequent PID calculations. When the DC transmission system is in no-load mode or load mode, the logic module ② is used to determine whether the machine-side circuit breaker signal is in the closed state. If it is in the closed state (y=1), the DC transmission system is judged to be in the load state. If it is in the open state (y=0), the DC transmission system is judged to be in the no-load state.

[0068] If the DC power transmission system is in no-load mode, the system frequency difference Δf is directly transmitted to the no-load PID calculation module for calculation. If the DC power transmission system is in load mode, it is also necessary to determine whether it is a network mode (connected to the large power grid) or an island mode (connected to DC). The judgment logic uses logic module ③ to determine whether the AC line switch (y=1) is in a network state and the AC line switch (y=0) is in an island state;

[0069] If the DC transmission system is judged to be in the networking mode, it will be further judged whether the actual frequency f of the DC transmission system is greater than 50.5Hz or less than 49.5Hz; if the actual frequency f is greater than 50.5Hz or less than 49.5Hz, the DC transmission system will be forced to enter the isolated mode; in the isolated mode, the system frequency difference Δf will pass through the isolated dead zone and enter the isolated PID calculation logic. If the actual frequency f is less than 50.5Hz and greater than 49.5Hz, the DC transmission system will maintain the networking mode, and the system frequency difference Δf will pass through the networking dead zone and enter the networking PID calculation logic;

[0070] If the DC transmission system is judged to be in island mode, it will further judge whether the actual frequency f of the DC transmission system is greater than 50.5Hz or less than 49.5Hz. If the actual frequency f is greater than 50.5Hz or less than 49.5Hz, the DC transmission system will be forced to enter the isolated grid mode; the system frequency difference Δf will pass through the isolated grid dead zone and enter the isolated grid PID calculation logic. If the actual frequency f is less than 50.5Hz and greater than 49.5Hz, the DC transmission system will maintain the island mode operation, and the system frequency difference Δf will pass through the isolated grid dead zone and enter the isolated grid PID calculation logic;

[0071] Among them, in the logic module⑧, the calculation results of the no-load, networking, isolated network, and island PID calculation logic, the quantity that satisfies the state signal selection logic through the selection of the island signal, the isolated network signal, and the no-load signal are directly output as the output of the PID module, and the output of the PID module is used as the primary frequency modulation control quantity YPID of the opening control. The primary frequency modulation control quantity of the opening is added to the no-load opening Ynoload to form the opening control Yset, which is sent to the closed-loop feedback logic of the actuator, and the water gate control quantity of the production turbine is controlled by the actuator and the relay to be sent to the guide vane system of the turbine generator unit, and the generated output is the mechanical power of the unit. In other embodiments, the turbine can also be other power drive sources, and the guide vane system of the turbine generator unit can also be other load types.

[0072] From the above, it can be seen that the existing DC transmission system switches the operating mode through the control logic of the speed regulator due to the control logic of entering the isolated network logic judgment ⑦ in the island mode. In the island mode, it will enter the isolated network mode, which will cause the DC transmission system to appear in the DC transmission system networking mode. During the switching process of the island mode, the isolated network mode of the unit is controlled by the slow retreat FLC to increase or decrease the power, resulting in the DC transmission system being unstable for a long time, causing certain risks to the DC transmission system.

[0073] The embodiments of the present application provide an optimized control method, device and equipment for switching the operating modes of a DC island system, which solves the technical problem that the existing frequency modulation strategy does not meet the requirements of fast control frequency stability in conversion between island mode, networking mode and arc network mode, and there are additional oscillations, posing a threat to the stability of the DC transmission system.

[0074] Embodiment 1:

[0075] Figure 6 This is a flowchart of the steps of the optimization control method for switching the operation mode of the DC island system described in the embodiment of the present application. Figure 7 This is an optimization control logic diagram of the optimization control method for switching the operation mode of the DC island system described in the embodiment of the present application, Figure 8 This is an optimized control logic diagram of an optimized control method for switching operation modes of a DC island system described in another embodiment of the present application.

[0076] like Figures 6 to 8 As shown, the embodiment of the present application provides an optimization control method for switching the operation mode of a DC island system, comprising the following steps:

[0077] S1. Obtain the operation mode type and system frequency difference of the DC island system.

[0078] It should be noted that in step S1, the operation mode type and the system frequency difference of the DC island system are determined, and the system frequency difference is calculated by the difference between the actual frequency and the target frequency of the DC island system.

[0079] S2. If the operation mode type is the isolated grid mode in the isolated grid mode, a shielding strategy is adopted to prevent the DC island system from entering the isolated grid mode, so that the DC island system always maintains the operation in the isolated grid mode. The shielding strategy includes adjusting the upper limit value of the frequency dead zone in the isolated grid mode or setting the enable signal of the isolated grid mode to zero.

[0080] It should be noted that in step S2, the operation mode type is first determined according to step S1 to be an isolated network mode in an isolated island mode. Figure 7As shown, the first is to adjust the upper limit of the frequency dead zone in the isolated grid mode, automatically adjust the upper limit of the frequency dead zone in the isolated grid mode, so that the actual frequency of the DC island system cannot reach the upper limit of the frequency dead zone, and achieve the goal of enlarging the frequency dead zone so that the DC island system cannot enter the isolated grid mode, ensuring that the DC island system always maintains the island mode after the networking mode of the DC island system switches to the island mode. Figure 8 As shown, the second is to set the enable signal of the isolated network mode to zero, which can be understood as directly forcing the enable signal of the isolated network mode to 0, so that the isolated network mode cannot be entered in the isolated network mode, and ensure that the DC island system always maintains the island mode after the networking mode is switched to the island mode; at the same time, the control method of the isolated network mode in the networking mode is retained to ensure the flexibility of switching various control methods in the networking mode. In the island mode, the optimized control method for switching the operation mode of the DC island system gives priority to ensuring the frequency stability of the DC island system and the safety of the entire DC island system in the island mode, so as to achieve faster system frequency stability and the stability of the entire island system in the switching process between the networking mode and the island mode.

[0081] In an embodiment of the present application, the optimization control method for switching the operating mode of the DC island system adopts a shielding strategy to prevent the DC island system from entering the isolated grid mode when the operating mode type of the DC island system is the isolated grid mode under the island mode, so as to avoid the mutual influence of the dual control of the island mode control and the isolated grid mode control, which leads to the problem of the stability of the DC island system being destroyed.

[0082] The present application provides an optimization control method for switching the operation mode of a DC island system, the method comprising obtaining the operation mode type and the system frequency difference of the DC island system; if the operation mode type is an isolated grid mode under the island mode, a shielding strategy is adopted to prevent the DC island system from entering the isolated grid mode, so that the DC island system always maintains the operation in the island mode; wherein the shielding strategy includes adjusting the upper limit value of the frequency dead zone in the isolated grid mode or setting the enable signal of the isolated grid mode to zero. The optimization control method for switching the operation mode of a DC island system adopts a shielding strategy to prevent the DC island system from entering the isolated grid mode based on the operation mode type of the DC island system being an isolated grid mode under the island mode, so as to avoid the mutual influence of the dual control of the island mode control and the isolated grid mode control, resulting in the destruction of the stability of the DC island system; it solves the technical problem that the existing frequency modulation strategy does not meet the requirements of fast control frequency stability in the conversion between the island mode, the networking mode, and the arc grid mode, and there are additional oscillations, which threatens the stability of the DC transmission system.

[0083] It should be noted that the optimized control method for switching the operation mode of the DC island system can realize the function of shielding the isolated network mode in the island mode. The optimized control method for switching the operation mode of the DC island system ensures that the isolated network mode can be flexibly switched with other operation modes in the networking mode. However, through simple operations, the judgment of the isolated network mode in the switching of the networking mode and the island mode in the DC island system can be shielded, which causes the primary frequency modulation control of the isolated network mode to interfere with the normal function of the DC frequency regulation mode to stabilize the system frequency. Compared with the existing frequency modulation strategy, the optimized control method for switching the operation mode of the DC island system avoids the maximum range of changes to the frequency modulation strategy controlled by the speed regulator, realizes the stable control of the speed regulator networking mode, and the DC island system of the networking mode and the island mode is smoothly switched. After entering the island mode, the DC frequency control function plays a leading role, and quickly smoothes the power shortage and frequency fluctuation of the DC island system; it can more effectively ensure the stability of the DC island system in the island mode.

[0084] In one embodiment of the present application, Figure 7 As shown in the figure, if the shielding strategy is to adjust the upper limit of the frequency dead zone in the isolated grid mode, the contents that prevent the DC island system from entering the isolated grid mode include:

[0085] Obtain the frequency dead zone adjustment value after adjusting the upper limit value of the frequency dead zone in the isolated network mode;

[0086] If the system frequency difference is not greater than the frequency dead zone adjustment value and the system frequency difference is not less than the negative frequency dead zone adjustment value, the enable signal of the isolated network mode is adjusted to 0, that is, the system frequency difference cannot enter the frequency dead zone of the isolated network mode;

[0087] If the system frequency difference is greater than the frequency dead zone adjustment value or the system frequency difference is less than the negative frequency dead zone adjustment value, the enable signal of the isolated network mode is adjusted to 1, and the frequency dead zone adjustment value is increased until the system frequency difference is not greater than the frequency dead zone adjustment value and the system frequency difference is not less than the negative frequency dead zone adjustment value.

[0088] It should be noted that the frequency dead zone adjustment value can be selected as 50Hz. When the system frequency difference is greater than the frequency dead zone adjustment value or the system frequency difference is less than the negative frequency dead zone adjustment value, the enable signal of the isolated network mode is adjusted to 1, and the system frequency difference of the DC island system can pass through the isolated network dead zone and enter the isolated network PID calculation logic; that is, the DC island system is in the isolated network mode and operates in the isolated network mode. During the process of switching the DC island system to this operating mode type, there are additional oscillations, which threaten the stability of the DC island system. Therefore, the optimization control method for switching the operating mode of the DC island system needs to increase the upper limit value of the frequency dead zone in the isolated network mode, that is, increase the value of the frequency dead zone adjustment value, amplify the frequency dead zone of the isolated network mode, and make it impossible to enter the isolated network mode.

[0089] In one embodiment of the present application, in step S1, the operation mode type of the DC island system includes:

[0090] Obtain the actual frequency of the DC island system and the disconnection status of the AC line;

[0091] Determine whether the DC island system is operating in a networking mode or an island mode according to the disconnection status;

[0092] When the DC island system is in the networking mode or the island mode, the actual frequency is compared with the frequency threshold to determine whether the operation mode type of the DC island system is the isolated network mode in the networking mode or the operation mode type of the DC island system is the isolated network mode in the island mode;

[0093] Among them, according to the comparison between the actual frequency and the frequency threshold, determining that the operation mode type of the DC island system is the isolated network mode in the networking mode or the operation mode type of the DC island system is the isolated network mode in the island mode includes: if the actual frequency is not within the frequency threshold range, then the operation mode type of the DC island system is the isolated network mode in the networking mode or the operation mode type of the DC island system is the isolated network mode in the island mode.

[0094] It should be noted that the disconnection state of the AC line includes the closing state and the opening state of the switch on the AC line. When the disconnection state of the AC line is the closing state, the DC island system is in the networking mode; when the disconnection state of the AC line is the opening state, the DC island system is in the island mode. The frequency threshold includes an upper frequency threshold and a lower frequency threshold. When the actual frequency is greater than the lower frequency threshold and less than the upper frequency threshold, that is, the actual frequency is within the frequency threshold range, the operation mode type of the DC island system is the networking mode in the networking mode or the operation mode type of the DC island system is the island mode in the island mode; when the actual frequency is less than the lower frequency threshold or greater than the upper frequency threshold, that is, the actual frequency is not within the frequency threshold range, the operation mode type of the DC island system is the isolated network mode in the networking mode or the operation mode type of the DC island system is the isolated network mode in the island mode. Among them, the upper frequency threshold and the lower frequency threshold can be set according to demand. Preferably, the lower frequency threshold can be selected as 49.5Hz, and the upper frequency threshold can be selected as 50.5Hz.

[0095] In one embodiment of the present application, the optimization control method for switching the operating mode of the DC island system includes: if the operating mode type of the DC island system is the isolated network mode in the networking mode, the frequency dead zone value in the isolated network mode is not adjusted; if the operating mode type of the DC island system is the isolated network mode in the island mode, a shielding strategy is adopted to prevent the DC island system from entering the isolated network mode.

[0096] It should be noted that the optimization control method for switching the operating mode of the DC island system is based on the operating mode type of the DC island system being the isolated grid mode under the networking mode, and the control logic of the existing frequency modulation strategy is used to continue switching the operating mode of the DC island system.

[0097] In the embodiments of the present application, Figure 7 and Figure 8 As shown, the working principle of the optimization control method for switching the operation mode of the DC island system is:

[0098] The circuit breaker at the machine end is closed to enter the load mode, and the circuit breaker of the AC line is closed to enter the networking mode. If the actual frequency f of the DC island system meets the frequency threshold range of 49.5Hz to 50.5Hz, it will enter the networking PID calculation after passing through the networking dead zone, and output the opening control amount of Ypid; if it is judged that the actual frequency f of the DC island system meets the frequency lower limit threshold of 49.5Hz or the frequency upper limit threshold is greater than 50.5Hz, it will enter the isolated network mode under the networking mode, and enter the isolated network PID calculation through the isolated network dead zone, output the opening control amount of Ypid, and then the unit will adjust the power output through the execution structure, relay, and unit guide vane.

[0099] The circuit breaker at the machine end is closed to enter the load mode, and the circuit breaker of the AC line is opened to enter the island mode. If the actual frequency f of the DC island system meets the frequency threshold range of 49.5Hz to 50.5Hz, it will enter the island PID calculation after passing through the island dead zone and output the opening control value of Ypid. Figure 8 The logic shown is to change the original judgment that the actual frequency f satisfies the frequency lower limit threshold of 49.5Hz or greater than the frequency upper limit threshold of 50.5Hz, then enter the isolated network mode in the networking mode, and change the upper limit value of the frequency dead zone of 0.5Hz to the frequency dead zone adjustment value of 50Hz, which exceeds the normal fluctuation frequency range of the DC island system. This control logic will always be invalid, that is, it will not be possible to enter the isolated network dead zone in the island mode. Another processing method is to force the enable signal of the control logic in the isolated network mode to 0, so that in the island mode and the isolated network mode selection logic ⑦, the isolated network mode selection is always invalid. Both of these processing methods will make it impossible to enter the isolated network mode in the island mode, effectively avoiding the power fluctuation of the DC island system caused by entering the isolated network mode during the island regulation process.

[0100] Embodiment 2:

[0101] Fig. 9 A schematic diagram of the framework of an optimization control device for switching operating modes of a DC island system according to an embodiment of the present application.

[0102] like Fig. 9As shown, the embodiment of the present application provides an optimization control device for switching operation modes of a DC island system, including a data acquisition module 10 and an optimization control module 20;

[0103] A data acquisition module 10 is used to obtain the operation mode type and system frequency difference of the DC island system;

[0104] The optimization control module 20 is used for, if the operation mode type is the isolated grid mode in the isolated grid mode, adopting a shielding strategy to prevent the DC isolated grid system from entering the isolated grid mode, so that the DC isolated grid system always maintains the isolated grid mode operation;

[0105] The shielding strategy includes adjusting the upper limit value of the frequency dead zone in the isolated network mode or setting the enable signal of the isolated network mode to zero.

[0106] In the embodiment of the present application, the optimization control module 20 includes an adjustment parameter acquisition submodule, an optimization control submodule and an adjustment submodule;

[0107] The adjustment parameter acquisition submodule is used to obtain the frequency dead zone adjustment value after adjusting the upper limit value of the frequency dead zone in the isolated network mode;

[0108] The optimization control submodule is used to adjust the enable signal of the isolated network mode to 0 according to the system frequency difference being not greater than the frequency dead zone adjustment value and the system frequency difference being not less than the negative frequency dead zone adjustment value;

[0109] The adjustment submodule is used to adjust the enable signal of the isolated network mode to 1 according to the system frequency difference being greater than the frequency dead zone adjustment value or the system frequency difference being less than the negative frequency dead zone adjustment value, and increase the frequency dead zone adjustment value until the system frequency difference is not greater than the frequency dead zone adjustment value and the system frequency difference is not less than the negative frequency dead zone adjustment value.

[0110] In the embodiment of the present application, the data acquisition module 10 includes a data acquisition submodule, a first mode determination submodule, and a second mode determination submodule;

[0111] A data acquisition submodule is used to obtain the actual frequency of the DC island system and the disconnection status of the AC line;

[0112] The first mode determination submodule is used to determine whether the DC island system is operating in a networking mode or an island mode according to the disconnection state;

[0113] The second mode determination submodule is used to compare the actual frequency with the frequency threshold when the DC island system is in the networking mode or the island mode, and determine that the operating mode type of the DC island system is the isolated network mode in the networking mode or the isolated network mode in the island mode.

[0114] In the embodiment of the present application, the optimization control submodule 20 is also used to not adjust the frequency dead zone value in the isolated network mode according to the operating mode type of the DC island system being the isolated network mode under the networking mode; and to adopt a shielding strategy to prevent the DC island system from entering the isolated network mode according to the operating mode type of the DC island system being the isolated network mode under the island mode.

[0115] It should be noted that the content of the module in the device of Example 2 corresponds to the step content of the method in Example 1. The content of the optimization control method for switching the operation mode of the DC island system has been described in Example 1, and the module content of the optimization control device for switching the operation mode of the DC island system will not be described in detail in this embodiment.

[0116] Embodiment three:

[0117] Fig.10 A schematic diagram of a terminal device described in an embodiment of the present application.

[0118] like Fig.10 As shown, an embodiment of the present application provides a terminal device, including a processor and a memory;

[0119] A memory, used for storing program codes and transmitting the program codes to a processor;

[0120] The processor is used to execute the above-mentioned optimization control method for switching the operation mode of the DC island system according to the instructions in the program code.

[0121] It should be noted that the processor is used to execute the steps in the above-mentioned optimization control method embodiment for switching the operation mode of a DC island system according to the instructions in the program code. Alternatively, the processor implements the functions of each module / unit in the above-mentioned system / device embodiments when executing the computer program.

[0122] Exemplarily, the computer program may be divided into one or more modules / units, one or more modules / units are stored in a memory and executed by a processor to complete the present application. One or more modules / units may be a series of computer program instruction segments capable of completing a specific function, and the instruction segments are used to describe the execution process of the computer program in a terminal device.

[0123] The terminal device may be a computing device such as a desktop computer, a notebook, a PDA, or a cloud server. The terminal device may include, but is not limited to, a processor and a memory. Those skilled in the art will appreciate that this does not constitute a limitation on the terminal device, and may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the terminal device may also include input and output devices, network access devices, buses, etc.

[0124] The processor may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (dSIC), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc.

[0125] The memory may be an internal storage unit of the terminal device, such as a hard disk or memory of the terminal device. The memory may also be an external storage device of the terminal device, such as a plug-in hard disk equipped on the terminal device, a smart memory card (SmdrtMedid Cdrd, SMC), a secure digital (Secure Digitdl, SD) card, a flash memory card (Fldsh Cdrd), etc. Further, the memory may also include both an internal storage unit of the terminal device and an external storage device. The memory is used to store computer programs and other programs and data required by the terminal device. The memory may also be used to temporarily store data that has been output or is to be output.

[0126] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0127] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0128] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0129] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0130] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Redd-Only Memory), random access memory (RdM, Random Access Memory), disk or optical disk and other media that can store program codes.

[0131] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An optimization control method for switching operation modes of a DC island system, characterized in that: The following steps are involved: Obtain the operating mode type and system frequency difference of the DC island system; If the operation mode type is an isolated grid mode in an island mode, a shielding strategy is adopted to prevent the DC island system from entering the isolated grid mode, so that the DC island system always maintains the operation in the island mode; The shielding strategy includes adjusting the upper limit value of the frequency dead zone in the isolated network mode or setting the enable signal of the isolated network mode to zero; If the shielding strategy is to adjust the upper limit of the frequency dead zone in the isolated grid mode, the contents of preventing the DC island system from entering the isolated grid mode include: Obtaining a frequency dead zone adjustment value after adjusting the upper limit value of the frequency dead zone in the isolated network mode; If the system frequency difference is not greater than the frequency dead zone adjustment value and the system frequency difference is not less than the negative frequency dead zone adjustment value, adjusting the enable signal of the isolated network mode to 0; If the system frequency difference is greater than the frequency dead zone adjustment value or the system frequency difference is less than the negative frequency dead zone adjustment value, the enable signal of the isolated network mode is adjusted to 1, and the frequency dead zone adjustment value is increased until the system frequency difference is not greater than the frequency dead zone adjustment value and the system frequency difference is not less than the negative frequency dead zone adjustment value.

2. The optimization control method for switching operation modes of a DC island system according to claim 1, characterized in that: The frequency dead zone adjustment value is 50 Hz.

3. The optimization control method for switching operation modes of a DC island system according to claim 1, characterized in that: The contents for obtaining the operating mode type of the DC island system include: Obtaining the actual frequency of the DC island system and the disconnection state of the AC line; Determining, according to the disconnection state, whether the DC island system is operating in a networking mode or in the island mode; When the DC island system is in the networking mode or the island mode, the actual frequency is compared with the frequency threshold to determine whether the operation mode type of the DC island system is the isolated network mode in the networking mode or the operation mode type of the DC island system is the isolated network mode in the island mode.

4. The optimization control method for switching operation modes of a DC island system according to claim 3, characterized in that: Comparing the actual frequency with the frequency threshold to determine that the operating mode type of the DC island system is the isolated network mode in the networking mode or the operating mode type of the DC island system is the isolated network mode in the island mode includes: if the actual frequency is not within the frequency threshold range, then the operating mode type of the DC island system is the isolated network mode in the networking mode or the operating mode type of the DC island system is the isolated network mode in the island mode.

5. The optimization control method for switching operation modes of a DC island system according to claim 3, characterized in that: include: If the operation mode type of the DC island system is the isolated network mode under the networking mode, the frequency dead zone value in the isolated network mode will not be adjusted; if the operation mode type of the DC island system is the isolated network mode under the island mode, a shielding strategy is adopted to prevent the DC island system from entering the isolated network mode.

6. An optimization control device for switching operation modes of a DC island system, characterized in that: It includes a data acquisition module and an optimization control module; The data acquisition module is used to obtain the operation mode type and system frequency difference of the DC island system; The optimization control module is used for, if the operation mode type is an isolated grid mode in an island mode, adopting a shielding strategy to prevent the DC island system from entering the isolated grid mode, so that the DC island system always maintains the island mode operation; The shielding strategy includes adjusting the upper limit value of the frequency dead zone in the isolated network mode or setting the enable signal of the isolated network mode to zero; The optimization control module includes an adjustment parameter acquisition submodule, an optimization control submodule and an adjustment submodule; The adjustment parameter acquisition submodule is used to obtain the frequency dead zone adjustment value after adjusting the upper limit value of the frequency dead zone in the isolated network mode; The optimization control submodule is used to adjust the enable signal of the isolated network mode to 0 according to the system frequency difference being not greater than the frequency dead zone adjustment value and the system frequency difference being not less than the negative frequency dead zone adjustment value; The adjustment submodule is used to adjust the enable signal of the isolated network mode to 1, and increase the frequency dead zone adjustment value according to the system frequency difference being greater than the frequency dead zone adjustment value or the system frequency difference being less than the negative frequency dead zone adjustment value, until the system frequency difference is not greater than the frequency dead zone adjustment value and the system frequency difference is not less than the negative frequency dead zone adjustment value.

7. The optimization control device for switching operation modes of a DC island system according to claim 6, characterized in that: The data acquisition module includes a data acquisition submodule, a first mode determination submodule and a second mode determination submodule; The data acquisition submodule is used to obtain the actual frequency of the DC island system and the disconnection status of the AC line; The first mode determination submodule is used to determine whether the DC island system is operating in the networking mode or the island mode according to the disconnection state; The second mode determination submodule is used to compare the actual frequency with the frequency threshold when the DC island system is in the networking mode or the island mode, and determine that the operating mode type of the DC island system is the isolated network mode in the networking mode or the operating mode type of the DC island system is the isolated network mode in the island mode.

8. The optimization control device for switching operation modes of a DC island system according to claim 7, characterized in that: The optimization control submodule is also used for not adjusting the frequency dead zone value in the isolated network mode according to the operating mode type of the DC island system being the isolated network mode in the networking mode; and for adopting a shielding strategy to prevent the DC island system from entering the isolated network mode according to the operating mode type of the DC island system being the isolated network mode in the island mode.

9. A terminal device, characterized in that: including a processor and a memory; The memory is used to store program codes and transmit the program codes to the processor; The processor is used to execute the optimization control method for switching the operation mode of the DC island system according to any one of claims 1 to 5 according to the instructions in the program code.

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