Converter control mode switching method and system based on current saturation algorithm

Abstract

The invention discloses a current saturation algorithm-based converter control mode switching method and system, and the method comprises the steps: building an outer loop voltage control equation of a fault-free network-building converter, and defining that the converter operates in a constant voltage mode; current limitation of a device under the fault is considered, a dq-axis current reference value under the fault is generated based on a current saturation algorithm, and a current converter is defined to operate in a current limiting mode; after a fault occurs in the constant voltage mode, whether the current amplitude of the converter exceeds the saturation current amplitude which can be borne by the device at the fault moment is judged, and the converter enters the current limiting mode from the constant voltage mode to operate; in the current limiting mode, when a difference value between an actual value and a reference value of active power output by the converter is smaller than a given value, exiting the current limiting mode, and entering a constant voltage mode for operation; and finally, on the basis of a switching rule of the converter between the CVC mode and the CLC mode, obtaining a switching model after the network-forming converter suffers from a fault. According to the invention, automatic switching can be realized to avoid the device overcurrent problem, and the logic is simple and effective.

Description

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, the control technology of the converter 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, the grid-connected converter may lose synchronization, and even some large disturbances may trigger the current limit of the controller, turning the system into a switchable dynamic system.

[0003] Current saturation is a common problem for converters under extreme conditions such as high load or sudden short circuit. When the current exceeds the design capacity of the converter, the converter enters a saturated state, causing distortion of the output voltage or current waveform, which seriously affects the stability and power supply quality of the system. Traditional converter control strategies have problems of slow response and low control accuracy when dealing with current saturation problems, especially in complex power grid structures, where stable operation of the converter is crucial. Therefore, it is particularly important to develop a strategy that can effectively deal with current saturation problems and achieve fast and stable control. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a converter control mode switching method and system based on a current saturation algorithm in view of the deficiencies in the above-mentioned prior art, so as 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] The outer loop voltage control equation of the grid-type converter under fault-free condition 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;

[0008] Considering the current limitation of the device under fault, the converter operates in the 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;

[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, respectively, 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 loop 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.

[0017] Preferably, when calculating the inner loop current reference value, the current inner loop control dynamics are ignored, and the current actual value is equal to the reference value limited to the saturation current of the device, at which time 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, respectively, l is 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, respectively, l is the line reactance, θ is the converter synchronization angle, P c is the actual value of the active power output by the converter, 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, 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 no fault condition, 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 limitation of the device under fault, defines the converter to operate in the current limiting mode, and generates the d-axis and q-axis current reference values ​​and active power of the converter under fault based on the current saturation algorithm;

[0029] The first judgment module, in the 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 the current limiting mode from the constant voltage mode;

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

[0031] In a third aspect, a computer device comprises 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 above-mentioned 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 the processor implements the steps of the above-mentioned converter control mode switching method based on the current saturation algorithm when executing the computer program.

[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 method for switching the control mode of a converter based on a current saturation algorithm is proposed. By introducing a current saturation algorithm, the limitation of existing control technology is broken through, and a new idea is provided for further research and innovation in the field of converter control, which promotes the progress of power electronics technology. When a fault occurs in the constant voltage mode, the current may exceed the rated current carrying capacity of the converter. By introducing the current saturation algorithm, it is possible to quickly detect and judge whether the current amplitude exceeds the allowable range of the device, and automatically switch to the current limiting mode to prevent equipment damage. This mechanism effectively improves the safety of the system and ensures that the converter will not fail due to overcurrent under extreme conditions. In the current limiting mode, the difference between the active power output of the converter and the reference value is monitored in real time. When the difference is less than a given value, the current limiting mode is exited and restored to the constant voltage mode. This mechanism can not only protect the equipment, but also effectively balance the power output, avoid energy waste caused by excessive current limiting, and optimize the energy management of the entire system. The converter can automatically switch between CVC and CLC modes. When the system is in a fault state, the current limiting mode gives priority to ensuring that the current does not exceed the safety threshold of the equipment. After the fault is removed or alleviated, the system can automatically switch back to the constant voltage mode and resume normal operation. This flexible control switching improves the system's adaptability under different working conditions, avoids manual intervention, and improves the intelligence of the system.

[0037] Furthermore, when the system current rises due to a sudden load change or a fault, the saturation current of the device will become a limiting condition. Based on the current saturation algorithm, the current reference value is obtained, and the control system will limit the reference value 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 to operate in current limiting mode. The current limiting mode relies on a feedback control mechanism. By real-time monitoring of the difference between the actual current and the reference value, if the actual current is close to the saturation current, the control system will automatically adjust the reference value to keep it within a safe range to achieve effective protection and stability.

[0038] Furthermore, when the converter is operating in constant voltage mode, it will normally maintain the set output voltage. However, when a short circuit or other fault occurs, the current may increase rapidly and exceed the maximum saturation current amplitude of the device. At this time, in order to protect the device and maintain system stability, the converter will automatically switch to current limiting mode. The main purpose of current limiting mode is to limit the output current of the converter to the maximum saturation current to prevent overcurrent from damaging the device. Excessive current can cause the device to overheat or even damage. By limiting the current to the saturation current, the device can be effectively protected and its service life can be extended.

[0039] Furthermore, based on the current saturation algorithm and the preset mode switching rules, the logic is simpler and more effective than the complex multiple control algorithms. This simplified control design not only reduces the computational burden, but also improves the system's 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 It is a schematic diagram of the process of the present invention;

[0044] Figure 2 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 3 It is a schematic diagram of the switching process between the CVC mode and the CLC mode after a system failure of the present invention;

[0046] Figure 4 It is a schematic diagram of the structure of the control mode switching system of the grid-type converter based on the current saturation algorithm;

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

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

[0049] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] In the description of the present invention, it should be understood that the terms “include” and “comprises” indicate the presence of 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 specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0052] It should be further understood that the term "and / or" used in the present specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes these combinations. For example, A and / or B can represent: A exists alone, A and B exist at the same time, 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, third, etc. may be used to describe preset ranges, etc. in the embodiments of the present invention, these preset ranges should not be limited to these terms. These terms are only used to distinguish preset ranges from each other. For example, without departing from the scope of the 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 determining" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)", depending on the context.

[0055] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[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 a grid-type converter under no fault is established, and the converter is defined to operate in a constant voltage control (CVC) mode. Secondly, considering the current limitation of the device under fault, a dq axis current reference value under fault is generated based on a current saturation algorithm (CSA), and the converter is defined to operate in a current limiting current control (CVC) mode. control, CLC) mode; after a fault occurs in the constant voltage mode, it is determined whether 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 the current limiting mode from the constant voltage 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 a given value, the converter exits the current limiting mode and enters the constant voltage mode; finally, based on the switching rules of the converter between the CVC and CLC modes, a switching model for the grid-type converter after a fault occurs is obtained. The switching model can realize automatic switching based on the current saturation algorithm and the preset mode switching rules to avoid device overcurrent problems. Compared with complex multiple control algorithms, the logic 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 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, respectively,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 operating in CVC mode is c as follows:

[0063]

[0064] Among them, U s and U p are the voltage 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, generating 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 loop 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. In the normalized system, I cmax Usually 1.2 is taken.

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

[0070] P c =I cmax U s cos(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, it is determined whether 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 the current limiting mode from the constant voltage mode;

[0073] When the converter operates in CVC mode, the inner current loop dynamics are ignored, and 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 as:

[0074]

[0075] In order to prevent the device from overcurrent, the converter current I c Limit the maximum saturation current I cmax Within, it is necessary to switch to CLC mode, that is, limit the converter current to the saturation current. 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 from the CLC mode and enters the CVC mode;

[0079] The device cannot operate at saturation current for a long time and needs to exit from CLC mode and enter CVC mode to operate stably at a reasonable steady-state point. In order to avoid power mutation at the converter operation point, repeated switching between CLC mode and CVC mode will cause system oscillation. It is recommended to enter CVC mode when the actual value of 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 inverter 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 ≥Icmax →CLC mode

[0086] It will be appreciated by those skilled in the art that various aspects of the present invention may be implemented as systems, methods or program products. Therefore, various aspects of the present invention may be specifically implemented in the following forms, namely: complete hardware implementation, complete software implementation (including firmware, microcode, etc.), or a combination of hardware and software implementations, which may be 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] Among them, 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 limitation of the device under fault, defines the converter to operate in the current limiting mode, and generates the d-axis and q-axis current reference values ​​and active power of the converter under fault based on the current saturation algorithm;

[0090] The first judgment module, in the 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 the current limiting mode from the constant voltage mode;

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

[0092] In another embodiment of the present invention, a terminal device is provided, the terminal device includes a processor and a memory, 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, and is 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 condition 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; under 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 enters current limiting mode from constant voltage mode; under current limiting mode, when the difference between the actual value and the reference value of the active power output by the converter is less than the 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, and 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 on the processor 61. When the computer program 63 is executed by the processor 61, the converter control mode switching method based on the current saturation algorithm in the embodiment is implemented. To avoid repetition, it is not described one by one here. Alternatively, when the computer program 63 is executed by the processor 61, the functions of each model / unit in the converter control mode switching system based on the current saturation algorithm in the embodiment are implemented. To avoid repetition, it is not described one by one here.

[0095] The computer device 60 may be a computing device such as a desktop computer, a notebook, a PDA, or a cloud server. The computer device 60 may include, but is not limited to, a processor 61 and a memory 62. Those skilled in the art will appreciate that Figure 5 This is only an example of the computer device 60 and does not constitute a limitation of the computer device 60. It 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. A general-purpose processor may be a microprocessor or any conventional processor, etc.

[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 to be output.

[0099] See also Figure 6 , the terminal device is a chip, and the chip 600 of this embodiment includes a processor 622, which may be one or more, 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. In addition, the processor 622 may be configured to execute the computer program to execute the above-mentioned 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, wherein 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, for example, 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 also 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 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, and 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-VolatileMemory), 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 are loaded and executed by the processor as follows:

[0103] The outer loop voltage control equation of the grid-type converter under fault-free condition 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; under 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 enters current limiting mode from constant voltage mode; under current limiting mode, when the difference between the actual value and the reference value of the active power output by the converter is less than the 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, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually 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 in 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 as an example, wherein the system parameter design is shown in Table 1.

[0107] Table 1 Relevant parameter design of the example system

[0108]

[0109] In this embodiment, a disturbance is set so that the infinite bus voltage U s At t = 0.2 seconds, it drops to 0.1 pu, at t c = 0.13s later, it returns to U 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 variation of the converter active power and the angle provided by the active power synchronization control when the fault duration is 130ms is described; 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 current of the converter 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 condition is satisfied. 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 and operate stably in CVC mode.

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

[0115] The technicians in the relevant field can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In practical applications, the above-mentioned function allocation can be 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 in a processing unit, or each unit can exist physically separately, or two or more units can be integrated in 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, which will not be repeated here.

[0116] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions 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. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be 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 only schematic. For example, the division of the modules or 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 through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0119] 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.

[0120] In addition, each functional unit in each embodiment of the present invention 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.

[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 processes 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, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. 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, U disk, mobile hard disk, 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 generate 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 capable of directing a computer or other programmable data processing device to operate 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 A 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 operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0125] The above contents are 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: The outer loop voltage control equation of the grid-type converter under fault-free condition 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 the 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 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 inner loop d-axis and q-axis current reference values ​​output by the outer loop voltage control are and They are: Among them, U s and U p are the voltages at the infinite busbar and the grid connection point, respectively, l is the line reactance, and θ 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: Reference values ​​of d-axis and q-axis currents of converter under fault conditions and They are: in, and are the inner loop 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.

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 current inner loop 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 I c for: Among them, U s and U p are the voltages at the infinite busbar and the grid connection point, respectively, l is the line reactance, θ is the converter synchronization angle, and j is the 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: P c = I cmax U s cos(θ + φ), if I c ≥ I cmax → CLC mode Among them, U s and U p are the voltages at the infinite busbar and the grid connection point, respectively, l is the line reactance, θ is the converter synchronization angle, P c is the actual value of the active power output of the converter, 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, and j 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 no fault condition, 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 limitation of the device under fault, defines the converter to operate in the current limiting mode, and generates the d-axis and q-axis current reference values ​​and active power of the converter under fault based on the current saturation algorithm; The first judgment module, in the 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 the current limiting mode from the constant voltage mode; The second judgment module, in the current limiting mode, when the difference between the actual value of the active power output by the converter and the reference value is less than a given value, exits the current limiting mode and enters the constant voltage 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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