A method, system, device and medium for adaptive current limiting of a grid-forming converter

Abstract

The present application belongs to the technical field of transient synchronization control of hybrid system, and discloses a grid-forming converter adaptive current limiting method, system, device and medium, to solve the problem that the power angle deviation of grid-following converter and grid-forming converter is difficult to be cooperatively suppressed when the power grid fails. The method comprises the following steps: first, a first transient mathematical model is established when the grid voltage is normal, and the steady-state power angle of the two types of converters is calculated; when the output current of the grid-forming converter reaches the amplitude limit value, the current limiting mode is switched to and the voltage drop degree is detected; then, a second transient mathematical model after current limiting is established, and the steady-state power angle in the current limiting state is calculated; based on the principle of minimizing the difference between the steady-state power angles of the grid-forming converter before and after the failure, the initial value of the saturated current phase angle is determined; finally, in the control structure of the grid-forming converter, an additional active power control link is introduced to suppress the power angle deviation of the grid-following converter, and an additional saturated current phase angle control link is introduced to suppress the power angle deviation of the grid-forming converter itself.

Description

Technical Field

[0001] This invention belongs to the field of transient synchronization control technology for hybrid systems, and specifically relates to an adaptive current limiting method, system, device and medium for grid-type converters. Background Technology

[0002] Grid-connected converters, capable of simulating the operating characteristics of synchronous generators and actively providing voltage and frequency support to the grid, are considered an effective means to improve the stability of renewable energy grid-connected systems. In practical engineering, grid-connected and grid-connected converters are often connected to the grid together, forming a hybrid system. However, due to the different control mechanisms of the two types of converters—grid-connected converters rely on phase-locked loops to follow the grid phase, while grid-connected converters autonomously construct voltage and frequency—the dynamic coupling relationship between them is complex. Especially when grid faults occur, the mutual influence between converters may further deteriorate the transient synchronization stability of the system.

[0003] When a grid voltage dip occurs, the output current of a grid-connected converter increases rapidly. To protect power electronic devices from damage, grid-connected converters typically require current-limiting protection to restrict their output current within a safe threshold. Unlike grid-connected converters, which can function as current sources both before and after current limiting, the control characteristics of a grid-connected converter change fundamentally after current limiting is triggered, significantly impacting its output voltage and power output capabilities. Existing research indicates that under typical saturated current limiting strategies such as d-axis priority and q-axis priority, the selection of the saturated current phase angle has a significant impact on the transient parameters of the grid-connected converter, including its power angle characteristics and attraction domain. Appropriate selection of the saturated current phase angle helps improve the transient stability of the grid-connected converter.

[0004] However, the aforementioned studies primarily focus on the independent or grid-connected operation of a single grid-connected converter, without fully considering the coupling effect between grid-connected and grid-connected converters. In hybrid systems, the dynamics of the phase-locked loop (PLL) of the grid-connected converter and the dynamics of the active power loop (APL) of the grid-connected converter interact, leading to more complex transient behavior. After a grid fault triggers current limiting in the grid-connected converter, its power output capability changes, affecting the power angle response of the grid-connected converter through electrical coupling paths, and vice versa. Current current limiting strategies mostly focus only on the overcurrent protection and transient stability of the grid-connected converter itself, lacking coordinated suppression measures for the power angle deviation of the two types of converters in hybrid systems, making it difficult to simultaneously ensure the transient stability of both types of converters during fault processes. Summary of the Invention

[0005] Based on the aforementioned shortcomings and deficiencies in the prior art, one of the objectives of this invention is to at least solve one or more of the aforementioned problems in the prior art. In other words, one of the objectives of this invention is to provide an adaptive current limiting method, system, device, and medium for grid-connected converters that meets one or more of the aforementioned requirements, so as to simultaneously suppress the power angle offset of grid-connected converters and grid-connected converters during grid faults and improve the overall transient stability of the hybrid system.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an adaptive current limiting method for a grid-connected converter, applicable to a hybrid system consisting of a grid-connected converter and a grid-connected converter, comprising the following steps: S1. Obtain the active power and reactive power given by the grid dispatch, establish the first transient mathematical model of the hybrid system when the grid voltage is normal, and calculate the steady-state power angle of the grid-connected converter and the grid-connected converter when the grid voltage is normal based on the first transient mathematical model. S2. When the output current of the grid converter reaches the limit value, the degree of voltage drop in the grid is detected, and the control mode of the grid converter is switched to the current limiting mode. S3. Establish a second transient mathematical model of the hybrid system after current limiting of the grid-type converter, and calculate the steady-state power angle of the grid-type converter and the grid-connected converter under the current limiting state based on the second transient mathematical model; S4. Based on the principle of minimizing the difference between the steady-state power angle of the grid-type converter calculated by the first transient mathematical model before the fault and the steady-state power angle of the grid-type converter calculated by the second transient mathematical model after the fault, the initial value of the saturation current phase angle is determined. S5. In the control structure of the grid-type converter, an additional active power control loop is introduced to suppress the power angle deviation of the grid-type converter, and an additional saturated current phase angle control loop is introduced to suppress the power angle deviation of the grid-type converter itself.

[0007] As a preferred approach, step S1 establishes the first transient mathematical model of the hybrid system when the grid voltage is normal, specifically as follows: The line impedance of the hybrid system is expressed in terms of the magnitude and angle of the admittance. Based on the active power control equation, voltage regulation equation and phase-locked loop control equation of the grid-type converter, the first transient mathematical model is constructed.

[0008] As a preferred option: The current limiting mode described in step S2 adopts a saturated current limiting strategy; The saturation current limiting strategy decomposes the output current of the grid converter into d-axis and q-axis components. The d-axis component is determined by the magnitude of the saturated current and the cosine of the phase angle of the saturated current. The q-axis component is determined by the sine value of the saturation current amplitude and the sine value of the saturation current phase angle; After entering the current limiting mode, the active power reference value of the grid converter is reduced according to the ratio of the grid voltage amplitude after the fault to the grid voltage amplitude before the fault.

[0009] As a preferred embodiment, in step S3, a second transient mathematical model of the hybrid system after current limiting by the grid-type converter is established, specifically as follows: Based on the actual active power output expression of the grid-type converter and the q-axis component expression of the terminal voltage of the grid-connected converter under the current limiting mode, combined with the active power control equation of the grid-type converter and the phase-locked loop control equation of the grid-connected converter, the second transient mathematical model is constructed.

[0010] As a preferred embodiment, the difference mentioned in step S4 refers to: The absolute value of the difference between the steady-state power angle of the grid-type converter before the fault, calculated by the first transient mathematical model, and the steady-state power angle of the grid-type converter after the fault, calculated by the second transient mathematical model.

[0011] As a preferred option, the additional active power control step introduced in step S5 is as follows: The deviation between the steady-state power angle of the grid converter before the fault and the actual power angle of the grid converter after the fault is used as input. An additional active power adjustment is generated by the proportional-integral regulator and the additional active power adjustment is superimposed on the active power reference value of the grid converter. The proportional-integral regulator has preset proportional coefficients and integral coefficients.

[0012] As a preferred approach, the additional saturation current phase angle control element introduced in step S5 is specifically as follows: The deviation between the steady-state power angle of the grid-type converter before the fault and the actual power angle of the grid-type converter after the fault is used as input. An additional saturated current phase angle adjustment is generated by the proportional-integral regulator and the additional saturated current phase angle adjustment is superimposed on the initial value of the saturated current phase angle determined in step S4. The proportional-integral regulator has preset proportional coefficients and integral coefficients.

[0013] Secondly, the present invention provides an adaptive current limiting system for a grid-type converter, used to implement the adaptive current limiting method for a grid-type converter as described in the first aspect.

[0014] Thirdly, the present invention provides an electronic device, the electronic device including a memory, a processor and a computer program, wherein when the computer program is executed by the processor, it implements the adaptive current limiting method for grid-type converters as described in the first aspect.

[0015] Fourthly, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the adaptive current limiting method for grid-type converters as described in the first aspect.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. By establishing a first transient mathematical model and a second transient mathematical model of the hybrid system under normal grid voltage and after current limiting, this invention can accurately calculate the steady-state power angle of the grid-connected converter and the grid-connected converter before and after the fault, providing a precise quantitative basis for subsequent adaptive current limiting control.

[0017] 2. This invention determines the initial value of the saturated current phase angle based on the principle of minimizing the steady-state power angle difference of the grid-type converter before and after a fault. Compared with the traditional fixed phase angle current limiting strategies such as d-axis priority or q-axis priority, it can effectively reduce the power angle offset of the grid-type converter before and after a fault from the initial moment.

[0018] 3. This invention introduces an additional active power control loop and an additional saturated current phase angle control loop into the control structure of the grid-type converter. The former adjusts the active power reference value of the grid-type converter according to the power angle deviation of the grid-type converter, and the latter adjusts the saturated current phase angle according to the power angle deviation of the grid-type converter itself, thereby achieving coordinated suppression of power angle deviation of the two types of converters.

[0019] 4. Through the above-mentioned adaptive adjustment mechanism, the present invention can dynamically adjust the active power reference value and saturation current phase angle of the grid-connected converter during grid voltage drop faults, so that the power angle of the converter hardly shifts before and after the fault, which significantly improves the overall transient stability of the grid-connected hybrid system.

[0020] Further or more detailed beneficial effects will be described in conjunction with specific embodiments in the detailed implementation. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram illustrating an application scenario of the adaptive current limiting method for grid-type converters described in Embodiment 1 of the present invention.

[0023] Figure 2 This is a flowchart illustrating the adaptive current limiting method for a grid-type converter as described in an embodiment of the present invention.

[0024] Figure 3 This is a control block diagram of the adaptive current limiting method for grid-type converters described in an embodiment of the present invention.

[0025] Figure 4 This is a structural diagram of the adaptive current limiting system for the grid-type converter described in Embodiment 2 of the present invention.

[0026] Figure 5 This is a structural diagram of the electronic device described in Embodiment 3 of the present invention.

[0027] Figure 6 This is a comparison chart of the active power reference value, saturated current phase angle, GFMC power angle response and GFLC power angle response results under the traditional current limiting strategy and the adaptive current limiting strategy described in Embodiment 5 of the present invention.

[0028] Icon labels: 500. Electronic equipment; 501. Processor; 502. Communication bus; 503. User interface; 504. Network interface; 505. Memory. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0030] In the following description, several embodiments of the present invention are provided. Different embodiments can be substituted or combined. Therefore, the present invention can also be considered to include all possible combinations of the same and / or different embodiments described. Thus, if one embodiment includes features A, B, and C, and another embodiment includes features B and D, then the present invention should also be considered to include embodiments containing one or more other possible combinations of A, B, C, and D, even if such embodiments are not explicitly described in the following text.

[0031] The following description provides examples and does not limit the scope, applicability, or examples set forth in the claims. Changes may be made to the function and arrangement of the described elements without departing from the scope of the invention. Various processes or components may be appropriately omitted, substituted, or added to the various examples. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Furthermore, features described with respect to some examples may be combined into other examples.

[0032] To facilitate a better understanding of the embodiments of the present invention, its application scenarios will be explained before providing a detailed explanation of the specific implementation methods.

[0033] Please see Figure 1 , Figure 1 A schematic diagram of the application scenario of the adaptive current limiting method for the grid-type converter is shown. Figure 1 (a) shows the topology of the hybrid system, which includes renewable energy power generation devices, DC / AC three-phase inverter I with grid-connected control, DC / AC three-phase inverter II with grid-connected control, and AC power grid III. The renewable energy power generation devices and DC / AC three-phase inverters are connected to photovoltaic or energy storage on the DC side to achieve DC-AC conversion of renewable energy; the power grid can be considered as a three-phase ideal voltage source. Figure 1 Figure (b) shows the control block diagram of the grid-type converter, illustrating the implementation of its active power control and reactive power control. Figure 1 (c) is the control block diagram of the grid-type converter, which shows its synchronous control method based on phase-locked loop.

[0034] The adaptive current limiting method for grid-connected converters described in this specification is applied to hybrid systems formed by grid-connected and grid-connected converters being connected to the power grid. In these scenarios, the application of the adaptive current limiting method for grid-connected converters aims to improve the overall transient stability of the hybrid system by adaptively adjusting the active power reference value and saturation current phase angle of the grid-connected converter when a voltage drop fault occurs in the power grid, while suppressing the power angle deviation of the grid-connected and grid-connected converters.

[0035] The following is a brief explanation of the hybrid system, grid-connected converter, grid-connected converter, steady-state power angle, current limiting mode, saturation current phase angle, active power control loop, saturation current phase angle control loop, and proportional-integral regulator involved in the various embodiments of this specification: A hybrid system refers to a power system formed by grid-connected converters and grid-connected converters connected to the power grid, with the two types of converters being coupled to each other through electrical lines.

[0036] A grid-following converter (GFLC) is a converter that relies on a phase-locked loop to follow the phase of the power grid and output current. Its control characteristics can be equivalent to a current source before and after current limiting. It is mainly used to feed the power generated by new energy power generation equipment into the power grid.

[0037] A grid-forming converter (GFMC) is a converter that simulates the operating characteristics of a synchronous generator and actively constructs voltage and frequency. It can provide voltage and frequency support for the power grid, and its control characteristics will change fundamentally after current limiting is triggered.

[0038] Steady-state power angle refers to the phase difference between the converter terminal voltage and the grid voltage. It is used to characterize the synchronization state between the converter and the grid and is one of the key indicators for judging the transient stability of a hybrid system.

[0039] Current limiting mode refers to the control mode switched to when the output current of the grid-connected converter reaches the limit value. In this mode, the output current of the grid-connected converter is limited to within a safe threshold to prevent damage to power electronic devices due to overcurrent.

[0040] The saturation current phase angle refers to the phase angle between the saturation current and the d-axis determined by the active power loop in a grid-type converter under current-limiting mode. This phase angle determines the distribution ratio of the saturation current in the d-axis and q-axis components, and is an important parameter affecting the transient stability of the grid-type converter.

[0041] The active power control loop refers to the control loop used to adjust the active power reference value of the grid-connected converter. This loop takes the power angle deviation of the grid-connected converter as input, generates an additional adjustment amount through a proportional-integral regulator, and adds it to the active power reference value to suppress the power angle deviation of the grid-connected converter.

[0042] The saturation current phase angle control loop refers to the control loop used to adjust the saturation current phase angle. This loop takes the power angle deviation of the grid-type converter itself as input, generates an additional adjustment amount through a proportional-integral regulator, and adds it to the initial value of the saturation current phase angle to suppress the power angle deviation of the grid-type converter itself.

[0043] A proportional-integral (PI) controller is a type of controller that uses proportional and integral operations, and has preset proportional and integral coefficients. This controller generates a corresponding output adjustment based on the input deviation signal, causing the controlled variable to gradually approach the target value.

[0044] Example 1: like Figure 2 As shown, this embodiment provides an adaptive current limiting method for a grid-type converter, which is applied to a hybrid system consisting of a grid-connected converter and a grid-type converter, and includes the following steps S1 to S5.

[0045] Step S1: Obtain the active power setpoint and reactive power setpoint given by the power grid dispatch, establish the first transient mathematical model of the hybrid system when the power grid voltage is normal, and calculate the steady-state power angle of the grid-connected converter and the grid-connected converter when the power grid voltage is normal based on the first transient mathematical model.

[0046] Specifically, in this embodiment, the active power reference value and reactive power reference value provided by the power grid dispatch center are first obtained. To simplify the calculation, the line impedance of the grid-connected converter hybrid system is expressed in terms of angle as follows: The argument form of the line impedance is expressed as: (1), In formula (1): It is the admittance of the power grid side branch. It is the admittance of the branch where the grid-type converter is located; , , and These are the custom-defined hybrid system admittance, grid output admittance, grid output admittance, and mutual admittance; , , and These are the magnitudes of the hybrid system admittance, the grid output admittance, the grid output admittance, and the mutual admittance, respectively. , , and These are the arguments of the hybrid system admittance, the grid output admittance, the grid output admittance, and the mutual admittance.

[0047] Grid-type converters generate phase information by simulating the oscillation equations of a synchronous machine through their active power control loop, thereby achieving synchronization with the power grid. (2), In formula (2): and These represent the virtual inertia and damping coefficient, respectively. and These are the GFMC active power reference value and the actual active power output of the grid-type converter, respectively. and These are the rated angular frequency and the angular frequency of the power loop output, respectively. It is the phase angle of the terminal voltage of the GFMC grid-type converter.

[0048] GFMC Actual Active Output P 1 and reactive power output Q The expression is: (3), (4), In equations (3) and (4): It is the voltage amplitude of the power grid; and These are the terminal voltage amplitudes of GFMC and GFLC, respectively; The phase angle is output by the phase-locked loop; , , These are the grid current, the output current of the grid-connected converter GFMC, and the output current of the grid-connected converter GFLC. RE and IM represent the phase angle between the output current of the grid-connected converter and the d-axis determined by the phase-locked loop; RE and IM represent the real and imaginary parts of the complex number, respectively.

[0049] Considering the voltage regulation characteristics of GFMC, it can be expressed as: (5), In equation (5): This is the reactive power-voltage droop factor; and These are the GFMC reactive power reference value and the actual reactive power output, respectively.

[0050] Based on its actual output reactive power expression, the expression for the GFMC terminal voltage can be obtained as follows:

[0051] (6), In equation (6), A , B and The expressions are as follows: (7), The proportional-integral (PLL) stage is crucial for achieving synchronization in a GFLC. It synchronizes the q-axis component of the GFLC terminal voltage with the grid-connected converter through a proportional-integral (PI) stage. V 2q To achieve synchronization with the power grid, the phase information generated by the phase-locked loop (PLL) is represented as follows: (8), In equation (8): and These are the proportional and integral coefficients of the PLL, respectively.

[0052] According to the superposition theorem and the principle of coordinate transformation, the q-axis component of the terminal voltage of the GFLC grid converter in the rotating coordinate system is: (9), Combining the above expressions, the transient stability mathematical model of the hybrid system under normal grid voltage can be obtained as follows: (10) After receiving the active and reactive power commands from the power grid dispatching system, the transient stability mathematical model of the hybrid system can be solved to calculate the steady-state power angle of the grid-connected converter when the grid voltage is normal. and the steady-state power angle of the grid converter .

[0053] Step S2: When the output current of the grid converter reaches the limit value, detect the degree of voltage drop in the grid and switch the control mode of the grid converter to the current limiting mode.

[0054] Specifically, in this embodiment, when the output current of the grid-connected converter reaches the limit value, the degree of voltage drop in the grid is detected. If the grid voltage drops below a preset threshold, the control mode of the grid-connected converter is switched from normal mode to current-limiting mode. A typical current-limiting strategy is shown in the following formula: (11), In equation (11): The saturation current of the grid-connected converter GFMC when the voltage drops and it enters the current-limiting state. The phase angle between the active power loop and the d-axis, i.e., the saturation current phase angle.

[0055] Specifically, after the limiting is triggered, the active power reference value of the grid-connected converter GFMC changes according to the following formula: (12), In equation (12): and These are the grid voltages before and after the fault, respectively. This is the active power reference value before the GFMC fault in the grid-type converter.

[0056] By dynamically adjusting the active power reference value based on the above formula, overcurrent can be limited while ensuring that the hybrid system reaches a new stable equilibrium point more quickly. Furthermore, even if the grid voltage drops significantly, transient instability due to the lack of a stable operating point can be avoided.

[0057] Step S3: Establish a second transient mathematical model of the hybrid system after current limiting of the grid-type converter, and calculate the steady-state power angle of the grid-type converter and the grid-connected converter under the current limiting state based on the second transient mathematical model.

[0058] Specifically, in this embodiment, after current limiting is activated, the key parameters affecting the transient stability of the hybrid system, namely the actual active power output P1 of the GFMC and the q-axis expression of the GFLC terminal voltage, are as follows: (13) (14) The synchronous stability of the hybrid system is still determined by the active power loop of the grid-connected converter GFMC and the phase-locked loop of the grid-connected converter GFLC, and its expression is: (15) The initial values ​​for this system of differential equations are given by the following equation: (16) In equations (13) to (16): The current amplitude after current limiting by GFMC; , , These are the impedances of the corresponding branches.

[0059] Based on this, the steady-state power angles of the grid-connected converter GFMC and the grid-connected converter GFLC in the hybrid system after the grid voltage fault causes the grid-connected converter GFMC to activate current limiting are respectively... and .

[0060] Step S4: Based on the principle of minimizing the difference between the steady-state power angle of the grid-type converter calculated by the first transient mathematical model before the fault and the steady-state power angle of the grid-type converter calculated by the second transient mathematical model after the fault, determine the initial value of the saturation current phase angle.

[0061] Specifically, in this embodiment, based on equations (10) and (15), the steady-state power angle difference before and after the fault is analyzed for different control parameters. and The effect of the grid-type converter GFMC active power reference value decreases, and the steady-state power angle difference of all converters in the hybrid system decreases; as the absolute value of the saturation current phase angle increases, the steady-state power angle difference of the grid-type converter GFMC decreases, while the steady-state power angle difference of the grid-type converter GFLC is not affected.

[0062] Based on the above analysis, the initial value of the saturation current phase angle should be selected to minimize the difference in power angle between the converters before and after the fault, so as to improve the overall transient stability of the system. The method for determining the initial value of the saturation current phase angle is as follows: (17) That is, the saturated current phase angle that minimizes the steady-state power angle difference of the grid-type converter before and after the fault is selected as the initial value.

[0063] Step S5: In the control structure of the grid-type converter, an additional active power control loop is introduced to suppress the power angle deviation of the grid-type converter, and an additional saturated current phase angle control loop is introduced to suppress the power angle deviation of the grid-type converter itself.

[0064] Specifically, in this embodiment, the expression for the additional active power control loop is as follows: (18) In equation (18): and These are the GFLC power angles of the grid-connected converter before and after the fault, respectively. and These are the proportional and integral coefficients of the active power PI regulator attached to the converter, respectively.

[0065] The expression for the additional saturation current phase angle control element is as follows: (19) In equation (19): and The GFMC power angles of the grid-type converter before and after the fault are respectively. and These are the proportional and integral coefficients of the PI regulator for the added saturation current phase angle of the converter.

[0066] This step takes the deviation between the steady-state power angle of the grid-type converter before the fault and the actual power angle of the grid-type converter after the fault as input, generates an additional saturation current phase angle adjustment amount through a proportional-integral regulator, and adds this adjustment amount to the initial value of the saturation current phase angle determined in step S4.

[0067] Through the above steps S1 to S5, this embodiment realizes adaptive current limiting of the grid-connected converter during grid faults, while suppressing the power angle deviation of the grid-connected converter and the grid-connected converter, thereby improving the overall transient stability of the hybrid system.

[0068] like Figure 3 As shown in the diagram, the control block diagram of the adaptive current limiting method for grid-type converters in this embodiment illustrates the connection relationships between the various control components. Figure 3 In this circuit, the active power control loop outputs the angular frequency, which is integrated to obtain the phase angle; the voltage control loop outputs the terminal voltage amplitude; simultaneously, the saturation current limiting strategy generates d-axis and q-axis current commands based on the saturation current phase angle, which are then controlled by the inner current loop and output as PWM signals to drive the converter. An additional active power control loop corrects the active power reference value based on the power angle deviation from the grid-connected converter, and an additional saturation current phase angle control loop corrects the saturation current phase angle based on the power angle deviation of the grid-connected converter itself.

[0069] Example 2: like Figure 4 As shown, this embodiment provides an adaptive current limiting system for a grid-type converter, used to implement the adaptive current limiting method for a grid-type converter as described in Embodiment 1, including: The data acquisition module is used to acquire the active power and reactive power setpoints and the real-time grid voltage given by the power grid dispatching system. The first modeling module is used to establish a first transient mathematical model of the hybrid system when the grid voltage is normal, and to calculate the steady-state power angle of the grid-connected converter and the grid-following converter when the grid voltage is normal based on the first transient mathematical model. The current limiting switching module is used to detect the degree of voltage drop in the grid voltage when the output current of the grid converter reaches the limit value, and switch the control mode of the grid converter to the current limiting mode. The second modeling module is used to establish a second transient mathematical model of the hybrid system after the grid-type converter is current-limited, and to calculate the steady-state power angle of the grid-type converter and the grid-connected converter under the current-limited state based on the second transient mathematical model; The initial value determination module is used to determine the initial value of the saturation current phase angle based on the principle of minimizing the difference between the steady-state power angle of the grid-type converter calculated by the first transient mathematical model before the fault and the steady-state power angle of the grid-type converter calculated by the second transient mathematical model after the fault. An adaptive control module is used to introduce an additional active power control loop into the control structure of the grid-connected converter to suppress the power angle deviation of the grid-connected converter, and to introduce an additional saturated current phase angle control loop to suppress the power angle deviation of the grid-connected converter itself.

[0070] Example 3: like Figure 5 As shown, this embodiment provides an electronic device, which may include: at least one processor, at least one network interface, a user interface, a memory, and at least one communication bus.

[0071] The communication bus can be used to enable communication between the various components mentioned above.

[0072] The user interface may include buttons, and optional user interfaces may also include standard wired interfaces and wireless interfaces.

[0073] The network interface may include, but is not limited to, Bluetooth modules, NFC modules, Wi-Fi modules, etc.

[0074] The processor may include one or more processing cores. It connects various parts of the electronic device via various interfaces and lines, executing instructions, programs, code sets, or instruction sets stored in memory, and accessing data stored in memory to perform various functions and process data. Optionally, the processor can be implemented using at least one hardware form of DSP, FPGA, or PLA. The processor may integrate one or more of the following: CPU, GPU, and modem. The CPU primarily handles the operating system, user interface, and applications; the GPU is responsible for rendering and drawing the content required for display; and the modem handles wireless communication. It is understood that the modem may also be implemented as a separate chip without being integrated into the processor.

[0075] The memory may include RAM or ROM. Optionally, the memory may include a non-transitory computer-readable medium. The memory can be used to store instructions, programs, code, code sets, or instruction sets. The memory may include a program storage area and a data storage area, wherein the program storage area may store instructions for implementing an operating system, instructions for at least one function (such as touch function, sound playback function, image playback function, etc.), instructions for implementing the above-described method embodiments, etc.; the data storage area may store data involved in the above-described method embodiments, etc. Optionally, the memory may also be at least one storage device located remotely from the aforementioned processor. The memory, as a computer storage medium, may include an operating system, a network communication module, a user interface module, and a rate-limiting application. The processor can be used to call the rate-limiting application stored in the memory and execute the steps of the adaptive rate-limiting method for grid-type converters mentioned in the foregoing embodiments.

[0076] Example 4: This embodiment provides a computer-readable storage medium storing instructions that, when executed on a computer or processor, cause the computer or processor to perform the above-described instructions. Figure 1 One or more steps in the illustrated embodiment. If the constituent modules of the above-described electronic device are implemented as software functional units and sold or used as independent products, they can be stored in the computer-readable storage medium.

[0077] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this specification are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in or transmitted through a computer-readable storage medium. The computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, Digital Subscriber Line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium accessible to a computer or a data storage device such as a server or data center that integrates one or more available media. The available media may be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., Digital Versatile Discs (DVDs)), or semiconductor media (e.g., Solid State Disks (SSDs)).

[0078] Those skilled in the art will understand that all or part of the processes in the method of Embodiment 1 described above can be implemented by a computer program instructing related hardware. This program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the methods described above. The aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks. Unless otherwise specified, the technical features of this embodiment and the implementation scheme can be combined arbitrarily.

[0079] Example 5: To verify the effectiveness of the adaptive current limiting method for a grid-type converter described in this specification, this embodiment uses the SIMULINK simulation platform to build a simulation system as follows. Figure 1 (a) shows a hybrid system model of grid-connected converter and grid-connected converter.

[0080] In this embodiment, the relevant parameters of the hybrid system are listed in Table 1.

[0081] Table 1:

[0082] During the simulation, a voltage dip fault was simulated in the power grid at 15 seconds. The voltage amplitude after the voltage dip was 0.45 times the voltage amplitude before the fault. Due to the significant disturbance to the power grid voltage, the saturation current limiting function of the grid-connected converter was triggered immediately upon the voltage dip. Before the fault, the grid-connected converter and the integrated grid converter output active power at 85% and 60% of their rated power, respectively.

[0083] To verify the effectiveness of the method proposed in this specification, this embodiment sets up three comparison schemes: Scheme 1 is the traditional d-axis priority current limiting strategy, Scheme 2 is the traditional q-axis priority current limiting strategy, and Scheme 3 is the adaptive current limiting strategy described in this specification. The three schemes are compared and simulated under the same fault conditions.

[0084] Simulation results are as follows Figure 6 As shown. Figure 6 (a) in the figure illustrates the change process of the active power reference value under voltage fault. When a voltage fault occurs, the adaptive current limiting method described in this specification can adaptively adjust the active power reference value of the grid-type converter to about 0.18pu. The traditional d-axis priority and q-axis priority current limiting strategies can only achieve the preliminary adjustment shown in equation (12). Figure 6 (b) shows the process of saturation current phase angle change under voltage fault. The adaptive current limiting method described in this specification can adaptively adjust the saturation current phase angle to about -1.8 rad, while the saturation current phase angle of the traditional d-axis priority and q-axis priority current limiting strategies remains unchanged. Figure 6 Figures (c) and (d) illustrate the power angle changes of grid-connected and grid-connected converters under voltage fault conditions. When using the d-axis priority current limiting strategy, the grid-connected converter exhibits the largest power angle shift after a fault, while the grid-connected converter experiences significant power angle oscillations. When using the q-axis priority current limiting strategy, the power angle shift of the grid-connected converter and the power angle oscillations after a fault are reduced, but the shift of the converter's power angle equilibrium point from its initial operating point is still unavoidable. In contrast, the adaptive current limiting strategy described in this specification can dynamically adjust the active power reference value and the saturation current phase angle during a fault, ensuring that the power angles of all converters in the hybrid system remain almost unchanged before and after the fault.

[0085] Based on the simulation comparison results above, this embodiment verifies that the adaptive current limiting method for grid-connected converters described in this specification can adaptively adjust the active power reference value and saturation current phase angle of the grid-connected converter during grid faults, effectively suppressing the power angle deviation of the grid-connected converter and the grid-connected converter, and significantly improving the overall transient stability of the hybrid system.

[0086] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, because according to the present invention, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0087] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0088] The above description is merely an exemplary embodiment of the present invention and should not be construed as limiting the scope of the invention. Any equivalent changes and modifications made in accordance with the teachings of this invention are still within the scope of this invention. Those skilled in the art will readily conceive of embodiments of the invention upon considering the specification and practicing the disclosure herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not described herein. The specification and embodiments are to be considered exemplary only, and the scope and spirit of the invention are defined by the claims.

Claims

1. An adaptive current limiting method for a grid-type converter, characterized in that, Applied to a hybrid system consisting of grid-connected and grid-connected converters, the steps include: S1. Obtain the active power and reactive power given by the grid dispatch, establish the first transient mathematical model of the hybrid system when the grid voltage is normal, and calculate the steady-state power angle of the grid-connected converter and the grid-connected converter when the grid voltage is normal based on the first transient mathematical model. S2. When the output current of the grid converter reaches the limit value, the degree of voltage drop in the grid is detected, and the control mode of the grid converter is switched to the current limiting mode. S3. Establish a second transient mathematical model of the hybrid system after current limiting of the grid-type converter, and calculate the steady-state power angle of the grid-type converter and the grid-connected converter under the current limiting state based on the second transient mathematical model; S4. Based on the principle of minimizing the difference between the steady-state power angle of the grid-type converter calculated by the first transient mathematical model before the fault and the steady-state power angle of the grid-type converter calculated by the second transient mathematical model after the fault, the initial value of the saturation current phase angle is determined. S5. In the control structure of the grid-type converter, an additional active power control loop is introduced to suppress the power angle deviation of the grid-type converter, and an additional saturated current phase angle control loop is introduced to suppress the power angle deviation of the grid-type converter itself.

2. The adaptive current limiting method for a grid-type converter according to claim 1, characterized in that, Step S1 establishes the first transient mathematical model of the hybrid system when the grid voltage is normal, specifically as follows: The line impedance of the hybrid system is expressed in terms of the magnitude and angle of the admittance. Based on the active power control equation, voltage regulation equation and phase-locked loop control equation of the grid-type converter, the first transient mathematical model is constructed.

3. The adaptive current limiting method for a grid-type converter according to claim 1, characterized in that: The current limiting mode described in step S2 adopts a saturated current limiting strategy; The saturation current limiting strategy decomposes the output current of the grid converter into d-axis and q-axis components. The d-axis component is determined by the magnitude of the saturated current and the cosine of the phase angle of the saturated current. The q-axis component is determined by the sine value of the saturation current amplitude and the sine value of the saturation current phase angle; After entering the current limiting mode, the active power reference value of the grid converter is reduced according to the ratio of the grid voltage amplitude after the fault to the grid voltage amplitude before the fault.

4. The adaptive current limiting method for a grid-type converter according to claim 1, characterized in that, In step S3, the second transient mathematical model of the hybrid system after current limiting by the grid-type converter is established, specifically as follows: Based on the actual active power output expression of the grid-type converter and the q-axis component expression of the terminal voltage of the grid-connected converter under the current limiting mode, combined with the active power control equation of the grid-type converter and the phase-locked loop control equation of the grid-connected converter, the second transient mathematical model is constructed.

5. The adaptive current limiting method for a grid-type converter according to claim 1, characterized in that, The difference mentioned in step S4 refers to: The absolute value of the difference between the steady-state power angle of the grid-type converter before the fault, calculated by the first transient mathematical model, and the steady-state power angle of the grid-type converter after the fault, calculated by the second transient mathematical model.

6. The adaptive current limiting method for a grid-type converter according to claim 1, characterized in that, The additional active power control mechanism introduced in step S5 is as follows: The deviation between the steady-state power angle of the grid converter before the fault and the actual power angle of the grid converter after the fault is used as input. An additional active power adjustment is generated by the proportional-integral regulator and the additional active power adjustment is superimposed on the active power reference value of the grid converter. The proportional-integral regulator has preset proportional coefficients and integral coefficients.

7. The adaptive current limiting method for a grid-type converter according to claim 1, characterized in that, The additional saturation current phase angle control element introduced in step S5 is as follows: The deviation between the steady-state power angle of the grid-type converter before the fault and the actual power angle of the grid-type converter after the fault is used as input. An additional saturated current phase angle adjustment is generated by the proportional-integral regulator and the additional saturated current phase angle adjustment is superimposed on the initial value of the saturated current phase angle determined in step S4. The proportional-integral regulator has preset proportional coefficients and integral coefficients.

8. An adaptive current limiting system for a grid-type converter, characterized in that, This method is used to implement the adaptive current limiting method for grid-type converters as described in any one of claims 1 to 7.

9. An electronic device, the electronic device comprising a memory, a processor, and a computer program, characterized in that, When the computer program is executed by the processor, it implements the adaptive current limiting method for grid-type converters as described in any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the adaptive current limiting method for grid-type converters as described in any one of claims 1 to 7.

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