A method and system for switching converter control modes based on current saturation algorithm

Abstract

The present invention discloses a converter control mode switching method and system based on a current saturation algorithm. The method establishes an outer loop voltage control equation for a grid-type converter under fault-free conditions and defines the converter as operating in a constant voltage mode. Considering the current limit of devices under fault conditions, a dq axis current reference value under fault conditions is generated based on the current saturation algorithm and the converter is defined as operating in a current-limited mode. After a fault occurs in the constant voltage mode, the method determines whether the converter's current amplitude at the moment of the fault exceeds the saturated current amplitude that the device can withstand, and the converter switches from the constant voltage mode to the current-limited mode. In the current-limited mode, when the difference between the actual value of the converter's output active power and the reference value is less than a given value, the converter exits the current-limited mode and enters the constant voltage mode. Finally, based on the converter's switching rules between CVC and CLC modes, a switching model for the grid-type converter after a fault occurs is derived. The present invention can achieve automatic switching to avoid device overcurrent problems, with simple and effective logic.

Description

Technical Field

[0001] The present invention belongs to the field of electric power technology, and particularly relates to a converter control mode switching method and system based on a current saturation algorithm. Background Art

[0002] In modern power systems, with the rapid growth of renewable energy access and the continuous development of power electronics technology, converters play a key role in energy conversion and power transmission. In particular, converters are widely used in DC transmission, microgrids, and grid-connected scenarios of various renewable energy sources (such as wind power and photovoltaics). However, with the increasing complexity of the power grid, converter control technology faces higher requirements, including dynamic response speed, anti-disturbance capability, and current saturation problems. Studies have shown that in the event of a severe AC fault, grid-connected converters may lose synchronization, and even some large disturbances may trigger the current limit of the controller, transforming the system into a switchable dynamic system.

[0003] Current saturation is a common problem in converters under extreme conditions such as high loads or sudden short circuits. When the current exceeds the converter's design capacity, the converter enters a saturated state, causing distortion in the output voltage or current waveform, seriously impacting system stability and power supply quality. Traditional converter control strategies suffer from slow response and low control accuracy when addressing current saturation. This is especially true in complex power grid structures, where stable converter operation is crucial. Therefore, developing a strategy that can effectively address current saturation and achieve fast and stable control is crucial. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the deficiencies in the above-mentioned prior art and provide a converter control mode switching method and system based on a current saturation algorithm, which is used to solve the technical problem of how to avoid device overcurrent after a grid-type converter suffers a fault.

[0005] The present invention adopts the following technical solutions:

[0006] A method for switching a converter control mode based on a current saturation algorithm comprises the following steps:

[0007] Establish the outer loop voltage control equation of the grid-type converter under fault-free conditions. The converter operates in constant voltage mode and generates the inner loop current reference value and active power under constant voltage mode.

[0008] Considering the current limitation of the device under fault conditions, the converter operates in current limiting mode, and generates the d-axis and q-axis current reference values ​​of the converter under fault conditions based on the current saturation algorithm.

[0009] In constant voltage mode, when a fault occurs, the current amplitude of the converter at the moment of fault exceeds the saturation current amplitude that the device can withstand, and the converter switches from constant voltage mode to current limiting mode.

[0010] In the current limiting mode, when the difference between the actual value of the converter output active power and the reference value is less than the given value, the converter exits the current limiting mode and enters the constant voltage mode.

[0011] Preferably, the converter operates in a constant voltage mode, and the inner loop d-axis and q-axis current reference values ​​output by the outer loop voltage control are and They are:

[0012]

[0013] Among them, U s and U p are the voltages at the infinite busbar and the grid connection point, X l is the line reactance, and θ is the converter synchronization angle.

[0014] Preferably, the d-axis and q-axis current reference values ​​of the converter under fault conditions are and They are:

[0015]

[0016] in, and are the inner ring d-axis and q-axis current reference values ​​obtained by the current saturation algorithm in CLC mode, I cmax and φ are the saturation current amplitude and phase angle that the device can withstand, respectively.

[0017] Preferably, when calculating the inner loop current reference value, the inner loop current control dynamics are ignored, and the actual current value is equal to the reference value limited to the saturation current of the device, at which point the converter is defined to operate in current limiting mode.

[0018] Preferably, in constant voltage mode, when a fault occurs, the condition for the converter to enter current limiting mode from constant voltage mode is that the current amplitude exceeds the maximum saturation current amplitude. In current limiting mode, the actual current value is limited to the saturation current of the device.

[0019] Preferably, the current amplitude I c for:

[0020]

[0021] Among them, U s and U p are the voltages at the infinite busbar and the grid connection point, X lis the line reactance, θ is the converter synchronization angle, and j is the imaginary unit.

[0022] Preferably, the switching control of the converter after a fault occurs is:

[0023]

[0024] P c =I cmax U s cos(θ+φ),if I c ≥I cmax →CLC mode

[0025] Among them, U s and U p are the voltages at the infinite busbar and the grid connection point, X l is the line reactance, θ is the converter synchronization angle, P c is the actual value of the converter output active power, is the reference value of the converter output active power, I cmax and φ are the saturation current amplitude and phase angle that the device can withstand, respectively, and j is an imaginary unit.

[0026] In a second aspect, an embodiment of the present invention provides a converter control mode switching system based on a current saturation algorithm, comprising:

[0027] The first generation module establishes the outer loop voltage control equation of the grid-type converter under fault-free conditions, defines the converter to operate in a constant voltage mode, and generates the inner loop current reference value and active power under the constant voltage mode;

[0028] The second generation module considers the current limit of the device under fault conditions, defines the converter to operate in current limiting mode, and generates the d-axis and q-axis current reference values ​​and active power of the converter under fault conditions based on the current saturation algorithm;

[0029] The first judgment module, in constant voltage mode, when a fault occurs and the current amplitude of the converter exceeds the saturation current amplitude that the device can withstand at the moment of the fault, the converter switches from constant voltage mode to current limiting mode;

[0030] The second judgment module is to exit the current limiting mode and enter the constant voltage mode when the difference between the actual value of the converter output active power and the reference value is less than a given value in the current limiting mode.

[0031] In a third aspect, a computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the converter control mode switching method based on the current saturation algorithm when executing the computer program.

[0032] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium, comprising a computer program, which, when executed by a processor, implements the steps of the above-mentioned converter control mode switching method based on the current saturation algorithm.

[0033] In a fifth aspect, a chip comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the steps of the converter control mode switching method based on the current saturation algorithm are implemented.

[0034] In a sixth aspect, an embodiment of the present invention provides an electronic device, comprising a computer program, which, when executed by the electronic device, implements the steps of the above-mentioned converter control mode switching method based on the current saturation algorithm.

[0035] Compared with the prior art, the present invention has at least the following beneficial effects:

[0036] A converter control mode switching method based on a current saturation algorithm overcomes the limitations of existing control technology by introducing a current saturation algorithm. This method provides new insights for further research and innovation in converter control, and promotes advancements in power electronics technology. When a fault occurs in constant voltage mode, the current may exceed the rated current capacity of the converter. By incorporating a current saturation algorithm, the method can quickly detect and determine whether the current amplitude exceeds the device's tolerance range and automatically switch to current limiting mode to prevent device damage. This mechanism effectively improves system safety, ensuring that the converter will not fail due to overcurrent under extreme conditions. In current limiting mode, the method monitors the difference between the converter's output active power and a reference value in real time. When the difference falls below a given value, the method exits current limiting mode and returns to constant voltage mode. This mechanism not only protects the device but also effectively balances power output, avoiding energy waste caused by excessive current limiting and optimizing overall system energy management. The converter can automatically switch between CVC and CLC modes. When the system is in a fault state, current limiting mode prioritizes ensuring that the current does not exceed the device's safety threshold. Once the fault is resolved or alleviated, the system automatically switches back to constant voltage mode and resumes normal operation. This flexible control switching improves the system's adaptability under different working conditions, avoids manual intervention, and enhances the system's intelligence.

[0037] Furthermore, when the system current rises due to a sudden load change or fault, the saturation current of the device becomes a limiting condition. Based on the current saturation algorithm, a current reference value is obtained, and the control system limits the reference value to below the saturation current. Ignoring the dynamics of the current inner loop control, it is assumed that the actual current can be instantaneously controlled to the reference value. At this time, the actual current is limited by the saturation current and is defined as operating in current limiting mode. Current limiting mode relies on a feedback control mechanism. By monitoring the difference between the actual current and the reference value in real time, if the actual current approaches the saturation current, the control system automatically adjusts the reference value to maintain it within a safe range, achieving effective protection and stability.

[0038] Furthermore, when the converter operates in constant voltage mode, it normally maintains the set output voltage. However, in the event of a short circuit or other fault, the current may increase rapidly, exceeding the device's maximum saturation current. At this point, to protect the device and maintain system stability, the converter automatically switches to current limiting mode. The primary purpose of current limiting mode is to limit the converter's output current to the maximum saturation current, preventing overcurrent damage to the device. Excessive current can cause device overheating or even damage. By limiting the current to the saturation current, the device is effectively protected and its service life is extended.

[0039] Furthermore, based on a current saturation algorithm and pre-set mode switching rules, the logic is simpler and more effective than complex multi-control algorithms. This simplified control design not only reduces the computational burden but also improves system response speed and control efficiency, helping to achieve efficient control with limited hardware resources.

[0040] It can be understood that the beneficial effects of the second aspect mentioned above can be found in the relevant description of the first aspect mentioned above, and will not be repeated here.

[0041] In summary, the present invention analyzes the current saturation characteristics and designs corresponding control strategies to achieve efficient and stable operation of the system. It can be promoted and applied to the control of various power electronic equipment, such as wind power generation, photovoltaic power generation, energy storage systems, flexible direct current transmission and other fields. It has broad engineering application value and can provide reference for the development of power electronics technology in other fields.

[0042] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Schematic diagram of the process of the present invention;

[0044] Figure 2 This is a schematic diagram of a system in which a single voltage source converter of the present invention is connected to an infinite power grid;

[0045] Figure 3Schematic diagram of the switching process between CVC mode and CLC mode after a system failure of the present invention;

[0046] Figure 4 The schematic diagram of the control mode switching system of the grid-type converter based on the current saturation algorithm is shown in FIG.

[0047] Figure 5 A schematic diagram of a computer device provided in accordance with an embodiment of the present invention;

[0048] Figure 6 The block diagram of a chip provided according to one embodiment of the present invention is shown. DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0050] In the description of the present invention, it is to be understood that the terms “include” and “comprise” indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0051] It should also be understood that the terms used in the present specification are only for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0052] It should be further understood that the term "and / or" as used in the present specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in the present invention generally indicates that the associated objects are in an "or" relationship.

[0053] It should be understood that although the terms "first," "second," and "third" may be used to describe preset ranges in embodiments of the present invention, these preset ranges should not be limited to these terms. These terms are merely used to distinguish one preset range from another. For example, without departing from the scope of embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0054] The word "if," as used herein, may be interpreted as "at the time of" or "when" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrases "if it is determined" or "if (stated condition or event) is detected" may be interpreted as "when it is determined" or "in response to the determination" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)," depending on the context.

[0055] The accompanying drawings illustrate various schematic diagrams of structures according to embodiments disclosed herein. These figures are not drawn to scale; for clarity, some details are exaggerated and some details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.

[0056] The present invention provides a method for switching the control mode of a converter based on a current saturation algorithm. First, the outer loop voltage control equation of the grid-type converter under no fault is established, and the converter is defined to operate in a constant voltage control (CVC) mode. Second, considering the current limitation of the device under fault, the dq axis current reference value under fault is generated based on the current saturation algorithm (CSA), and the converter is defined to operate in a current limiting (CCL) mode. Abstract: In order to solve the problem of overcurrent in the network converter, a switching model of the network converter after a fault is obtained based on the switching rules between CVC and CLC modes. The switching model can realize automatic switching to avoid device overcurrent problems based on the current saturation algorithm and the preset mode switching rules. Compared with the complex multiple control algorithms, the switching model is simpler and more effective.

[0057] See also Figure 1 The present invention provides a method for switching a converter control mode based on a current saturation algorithm, comprising the following steps:

[0058] S1. Establish the outer loop voltage control equation of the grid-type converter under no fault conditions and define the converter to operate in CVC mode;

[0059] The inner loop current reference value of the converter is output by the outer loop voltage control:

[0060]

[0061] in, and They are the inner loop d-axis and q-axis current reference values ​​output by the outer loop voltage control in CVC mode, U s and U p are the voltages at the infinite busbar and the grid connection point, X l is the line reactance, and θ is the converter synchronization angle.

[0062] For a single-machine infinite power system, since the dynamic process of internal current control is much faster than power control, the actual value of the converter current is considered to be equal to the reference value when calculating the active power. Without considering the loss, the active power P transmitted by the converter in CVC mode is c as follows:

[0063]

[0064] Among them, U s and U p are the voltages at the infinite busbar and the grid connection point, L l is the line inductance, ω s is the angular frequency of the infinite system, and θ is the converter synchronization angle.

[0065] S2. Considering the current limit of the device under fault, generate the dq axis current reference value under fault based on the current saturation algorithm (CSA);

[0066] The reference value of the dq axis current under fault is:

[0067]

[0068] in, and are the inner ring d-axis and q-axis current reference values ​​obtained by the current saturation algorithm in CLC mode, I cmax and φ are the saturation current amplitude and phase angle that the device can withstand, respectively. In the per-unit system, I cmax Usually 1.2 is taken.

[0069] When the inner loop current reference is calculated based on the above equation, ignoring the inner loop current control dynamics, the actual current is equal to the reference value limited to the saturation current of the device, and the active power transmitted is:

[0070] P c =I cmax U scos(θ+φ)

[0071] At this time, the converter is defined to operate in current limiting control (CLC) mode.

[0072] S3: After a fault occurs in the constant voltage mode, the converter determines whether the current amplitude of the converter exceeds the saturation current amplitude that the device can withstand at the moment of the fault. The converter switches from the constant voltage mode to the current limiting mode.

[0073] When the converter operates in CVC mode, ignoring the current inner loop dynamics, the actual current value is the same as the reference value. At this time, the converter current is obtained as Substitute the reference value obtained in step S1 and find the current amplitude:

[0074]

[0075] In order to prevent the device from overcurrent, the converter current I c Limit the maximum saturation current I cmax Therefore, the condition for the converter to switch from CVC mode to CLC mode is that the current amplitude exceeds the maximum saturation current amplitude:

[0076]

[0077] At this time, the converter operates in CLC mode, and the actual current value is limited to the saturation current of the device.

[0078] S4. When the actual value of the active power transmitted by the converter and the reference value are close to a given degree, the converter exits the CLC mode and enters the CVC mode;

[0079] The device cannot operate at saturation current for a long time and needs to exit CLC mode and enter CVC mode to stabilize operation at a reasonable steady-state point. In order to avoid sudden changes in power at the converter operating point, which may cause system oscillations due to repeated switching between CLC mode and CVC mode, enter CVC mode when the actual value of the active power transmitted by the converter is close to the reference value. For active power transmission in CLC mode:

[0080] P c =I cmax U s cos(θ+φ)

[0081] For any given ΔP, when When , the converter enters CVC mode.

[0082] S5. A control mode switching method for a grid-type converter based on a current saturation algorithm is used to obtain a switching model for a grid-type converter after a fault occurs.

[0083] The switching control of the converter after a fault occurs is:

[0084]

[0085] P c =I cmax U s cos(θ+φ),if I c ≥I cmax →CLC mode

[0086] Those skilled in the art will appreciate that various aspects of the present invention may be implemented as systems, methods, or program products. Accordingly, various aspects of the present invention may be implemented in the following forms: entirely in hardware, entirely in software (including firmware, microcode, etc.), or in a combination of hardware and software, collectively referred to herein as "circuits," "modules," or "platforms."

[0087] See also Figure 4 In another embodiment of the present invention, a converter control mode switching system based on a current saturation algorithm is provided. The system can be used to implement the above-mentioned converter control mode switching method based on a current saturation algorithm. Specifically, the converter control mode switching system based on a current saturation algorithm includes a first generation module, a second generation module, a first judgment module and a second judgment module.

[0088] The first generation module establishes the outer loop voltage control equation of the grid-type converter under fault-free conditions, defines the converter to operate in a constant voltage mode, and generates the inner loop current reference value and active power under the constant voltage mode;

[0089] The second generation module considers the current limit of the device under fault conditions, defines the converter to operate in current limiting mode, and generates the d-axis and q-axis current reference values ​​and active power of the converter under fault conditions based on the current saturation algorithm;

[0090] The first judgment module, in constant voltage mode, when a fault occurs and the current amplitude of the converter exceeds the saturation current amplitude that the device can withstand at the moment of the fault, the converter switches from constant voltage mode to current limiting mode;

[0091] The second judgment module is to exit the current limiting mode and enter the constant voltage mode when the difference between the actual value of the converter output active power and the reference value is less than a given value in the current limiting mode.

[0092] In another embodiment of the present invention, a terminal device is provided, which includes a processor and a memory, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions to implement the corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of the converter control mode switching method based on the current saturation algorithm, including:

[0093] The outer loop voltage control equation of the grid-type converter under fault-free conditions is established, the converter operates in constant voltage mode, and the inner loop current reference value and active power under constant voltage mode are generated; considering the current limitation of the device under fault, the converter operates in current limiting mode, and the d-axis and q-axis current reference values ​​of the converter under fault are generated based on the current saturation algorithm; in constant voltage mode, when a fault occurs, the current amplitude of the converter at the moment of the fault exceeds the saturation current amplitude that the device can withstand, and the converter enters current limiting mode from constant voltage mode; in current limiting mode, when the difference between the actual value and the reference value of the converter output active power is less than a given value, the converter exits current limiting mode and enters constant voltage mode.

[0094] See also Figure 5 The terminal device is a computer device. The computer device 60 of this embodiment includes: a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable by the processor 61. When executed by the processor 61, the computer program 63 implements the converter control mode switching method based on the current saturation algorithm of the embodiment. To avoid repetition, the details are not described here. Alternatively, when executed by the processor 61, the computer program 63 implements the functions of each model / unit in the converter control mode switching system based on the current saturation algorithm of the embodiment. To avoid repetition, the details are not described here.

[0095] The computer device 60 may be a desktop computer, a notebook computer, a PDA, a cloud server, or other computing devices. The computer device 60 may include, but is not limited to, a processor 61 and a memory 62. It will be understood by those skilled in the art that Figure 5 This is merely an example of the computer device 60 and does not constitute a limitation of the computer device 60 . The computer device 60 may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the computer device may also include input and output devices, network access devices, buses, etc.

[0096] The processor 61 may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor.

[0097] The memory 62 may be an internal storage unit of the computer device 60, such as a hard disk or memory of the computer device 60. The memory 62 may also be an external storage device of the computer device 60, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc. equipped on the computer device 60.

[0098] Furthermore, the memory 62 may include both an internal storage unit of the computer device 60 and an external storage device. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 may also be used to temporarily store data that has been output or is about to be output.

[0099] See also Figure 6 The terminal device is a chip. The chip 600 of this embodiment includes one or more processors 622 and a memory 632 for storing a computer program executable by the processor 622. The computer program stored in the memory 632 may include one or more modules, each corresponding to a set of instructions. Furthermore, the processor 622 may be configured to execute the computer program to implement the aforementioned converter control mode switching method based on the current saturation algorithm.

[0100] In addition, the chip 600 may further include a power supply component 626 and a communication component 650. The power supply component 626 may be configured to perform power management of the chip 600, and the communication component 650 may be configured to implement communication, such as wired or wireless communication, of the chip 600. In addition, the chip 600 may further include an input / output interface 658. The chip 600 may operate based on an operating system stored in the memory 632.

[0101] In another embodiment of the present invention, the present invention further provides a storage medium, specifically a computer-readable storage medium, which is a memory device in a terminal device for storing programs and data. It can be understood that the computer-readable storage medium here can include both the built-in storage medium in the terminal device and, of course, the extended storage medium supported by the terminal device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space. These instructions can be one or more computer programs. It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory (Non-Volatile Memory), such as at least one disk memory.

[0102] One or more instructions stored in a computer-readable storage medium may be loaded and executed by a processor to implement the corresponding steps of the converter control mode switching method based on the current saturation algorithm in the above embodiment; one or more instructions in the computer-readable storage medium may be loaded and executed by the processor to perform the following steps:

[0103] The outer loop voltage control equation of the grid-type converter under fault-free conditions is established, the converter operates in constant voltage mode, and the inner loop current reference value and active power under constant voltage mode are generated; considering the current limitation of the device under fault, the converter operates in current limiting mode, and the d-axis and q-axis current reference values ​​of the converter under fault are generated based on the current saturation algorithm; in constant voltage mode, when a fault occurs, the current amplitude of the converter at the moment of the fault exceeds the saturation current amplitude that the device can withstand, and the converter enters current limiting mode from constant voltage mode; in current limiting mode, when the difference between the actual value and the reference value of the converter output active power is less than a given value, the converter exits current limiting mode and enters constant voltage mode.

[0104] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0105] Using MATLAB, Figure 2 The simulation system shown is used to simulate and verify the control mode switching method of the grid-type converter proposed in the present invention.

[0106] by Figure 1 The method shown is used to analyze a system in which a GFM converter under synchronous power control is connected to an infinite power bus, where the system parameter design is shown in Table 1.

[0107] Table 1. Design of relevant parameters of the example system

[0108]

[0109] In this embodiment, a disturbance is set to make the infinite bus voltage U s At t = 0.2 seconds, it drops to 0.1 pu, at t c =Recover to U after 0.13s s , based on the current saturation algorithm, the system dynamic response of the grid-type converter control mode switching is considered as follows Figure 3 shown.

[0110] Figure 3 The figure describes the changes in the converter active power and the angle provided by the active power synchronization control when the fault duration is 130ms. When the infinite bus voltage drops to 0.1pu, the converter active power suddenly drops from point A to point B. Therefore, the converter active power moves along curve BC during the disturbance and then jumps to point D after the fault is eliminated.

[0111] It is worth noting that point D is located on the CLC mode; this is because the converter current is greater than the maximum saturation current that the device can withstand, that is, it satisfies I c ≥I cmax .

[0112] Since point G is an unstable equilibrium point in the CLC mode, the active power of the converter will continue to move along the DE curve. Once the difference between the actual active power value provided by PSL and the reference value is less than 0.02, the The system under study will switch to CVC mode operation.

[0113] Therefore, the converter will jump to point F and finally return to point A along curve FA, operating stably in CVC mode.

[0114] In summary, the converter control mode switching method and system based on the current saturation algorithm of the present invention can achieve effective switching and transient stability between the CVC mode and the CLC mode after the grid-type converter suffers a fault.

[0115] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In actual applications, the above-mentioned functions can be distributed and completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0116] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant description of other embodiments.

[0117] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed in the present invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present invention.

[0118] In the embodiments provided by the present invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For example, the division of the modules or units is merely a logical functional division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be through some interface, indirect coupling or communication connection of devices or units, and can be electrical, mechanical, or other forms.

[0119] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0120] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0121] If the integrated module / 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 present invention implements all or part of the process in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, it can implement the steps of the above-mentioned various method embodiments. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal and software distribution medium, etc. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

[0122] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices, and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of the processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of 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 processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0123] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0124] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0125] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for switching converter control modes based on a current saturation algorithm, characterized in that: The following steps are involved: Establish the outer loop voltage control equation of the grid-type converter under fault-free conditions. The converter operates in constant voltage mode and generates the inner loop current reference value and active power under constant voltage mode. Considering the current limitation of the device under fault, the converter operates in the current limiting mode, and the converter current under fault is generated based on the current saturation algorithm. d Axis and q Shaft current reference value; In constant voltage mode, when a fault occurs, the current amplitude of the converter at the moment of fault exceeds the saturation current amplitude that the device can withstand, and the converter switches from constant voltage mode to current limiting mode. In the current limiting mode, when the difference between the actual value of the converter output active power and the reference value is less than the given value, the converter exits the current limiting mode and enters the constant voltage mode.

2. The method for switching converter control modes based on current saturation algorithm according to claim 1, characterized in that: The converter operates in constant voltage mode, and the converter outputs the inner loop voltage controlled by the outer loop voltage. d Axis and q Shaft current reference value and They are: in, and are the voltages at the infinite busbar and the grid connection point, is the line reactance, is the converter synchronization angle.

3. The method for switching converter control modes based on current saturation algorithm according to claim 1, characterized in that: Fault converter d Axis and q Shaft current reference value and They are: in, and They are the inner loop obtained by the current saturation algorithm in current limiting mode. d Axis and q Shaft current reference value, and are the saturation current amplitude and phase angle that the device can withstand, respectively.

4. The method for switching converter control modes based on current saturation algorithm according to claim 3, characterized in that: When calculating the inner loop current reference value, the inner loop current control dynamics are ignored and the actual current value is equal to the reference value limited to the saturation current of the device. At this time, the converter is defined to operate in current limiting mode.

5. The method for switching converter control modes based on current saturation algorithm according to claim 1, characterized in that: In constant voltage mode, when a fault occurs, the condition for the converter to enter current limiting mode from constant voltage mode is that the current amplitude exceeds the maximum saturation current amplitude. In current limiting mode, the actual current value is limited to the saturation current of the device.

6. The method for switching converter control modes based on current saturation algorithm according to claim 5, characterized in that: Current amplitude for: in, and are the voltages at the infinite busbar and the grid connection point, is the line reactance, is the converter synchronization angle, Is an imaginary unit.

7. The method for switching converter control modes based on current saturation algorithm according to claim 1, characterized in that: The switching control of the converter after a fault occurs is: in, and are the voltages at the infinite busbar and the grid connection point, is the line reactance, is the converter synchronization angle, is the actual value of the converter output active power, is the reference value of the converter output active power, and are the saturation current amplitude and phase angle that the device can withstand, Is an imaginary unit.

8. A converter control mode switching system based on current saturation algorithm, characterized in that: include: The first generation module establishes the outer loop voltage control equation of the grid-type converter under fault-free conditions, defines the converter to operate in a constant voltage mode, and generates the inner loop current reference value and active power under the constant voltage mode; The second generation module considers the current limit of the device under fault, defines the converter to operate in current limiting mode, and generates the converter current under fault based on the current saturation algorithm. d Axis and q Shaft current reference and active power; The first judgment module, in constant voltage mode, when a fault occurs and the current amplitude of the converter exceeds the saturation current amplitude that the device can withstand at the moment of the fault, the converter switches from constant voltage mode to current limiting mode; The second judgment module is to exit the current limiting mode and enter the constant voltage mode when the difference between the actual value of the converter output active power and the reference value is less than a given value in the current limiting mode.

9. A computer-readable storage medium storing one or more programs, characterized in that: The one or more programs include instructions, which, when executed by a computing device, cause the computing device to perform the method of any one of claims 1 to 7.

10. A computing device, characterized in that include: One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include steps for executing the method according to any one of claims 1 to 7.

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