Current amplitude-voltage phase hybrid network configuration converter fault recovery method and system

Abstract

The present application belongs to the technical field of converter fault recovery, and proposes a current amplitude-voltage phase hybrid network converter fault recovery method and system. By revealing the switching characteristics of the current amplitude-voltage phase hybrid network control between the constant voltage control mode and the current limiting mode, the power angle operating range in the constant voltage control mode and the current limiting mode is determined. The fault recovery mechanism of the network converter under the current amplitude-voltage phase hybrid network control is revealed, the stable operating conditions of the current amplitude-voltage phase hybrid network control are determined, and the power angle boundary of the stable operating area is analyzed. By limiting the lower limit of the current limiting coefficient, the unstable area of the current amplitude-voltage phase hybrid network control is completely eliminated, and the global fault recovery capability of the network converter is guaranteed.

Description

Technical Field

[0001] This invention belongs to the technical field of converter fault recovery, and particularly relates to a method and system for fault recovery of converters with mixed current amplitude and voltage phase grids. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Grid-connected converters can independently adjust voltage amplitude and phase angle without relying on an external power grid, demonstrating the ability to autonomously build voltage amplitude and phase angle. They can autonomously establish system voltage and regulate frequency during normal operation. However, the overcurrent capacity that grid-connected converters can withstand is typically much lower than that of synchronous generators. To prevent damage from overcurrent during faults, current limiting control is crucial for grid-connected converters.

[0004] To ensure that grid-connected converters simultaneously limit fault current and support inertia during faults, existing literature proposes a novel cross-forming control (CFM) that combines current amplitude and voltage phase characteristics. This allows for precise fault current limiting without altering the virtual internal potential phase angle. In other words, CFM control combines voltage phase grid-connection with current amplitude grid-connection characteristics. This hybrid characteristic enables the grid-connected converter to maintain grid synchronization characteristics and provide inertia support during current limiting. From the perspective of the equivalent circuit, CFM control achieves current limiting only by adjusting the amplitude of the virtual internal potential; its phase is still generated by grid synchronization control, and the virtual impedance remains constant. However, during fault recovery, CFM control exhibits a significant instability region, during which it loses its fault current limiting capability. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides a fault recovery method and system for a grid converter with hybrid current amplitude and voltage phase, which can eliminate all unstable regions without compressing the original operating domain of CFM control, so that the grid converter under CFM control has global fault recovery capability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a fault recovery method for a hybrid current amplitude-voltage phase grid converter, comprising: The current switching condition of the grid-type converter under the mixed current amplitude-voltage phase grid control between the constant voltage control mode and the current limiting mode is analyzed as the power angle switching condition. Based on the power angle equation of the grid converter under the mixed current amplitude-voltage phase grid control in constant voltage control mode and current limiting mode, and combined with the power angle switching condition, the piecewise active power-power angle curve and unstable region are obtained. Based on the boundary of the unstable operating region of the grid-connected converter under mixed current amplitude and voltage phase grid control, the analytical power angle range of the unstable region is obtained; Considering the premise of not compressing the original feasible region of the mixed current amplitude-voltage phase network control, the lower limit of the current limiting coefficient of the ring current limiter is tuned to eliminate all unstable regions; wherein, the current limiting coefficient of the ring current limiter is introduced to scale the virtual internal potential amplitude to achieve current limiting.

[0007] Secondly, the present invention provides a fault recovery method for a hybrid current amplitude-voltage phase grid converter, comprising: The analysis module is configured to: analyze the current switching conditions of the grid-type converter under the mixed current amplitude-voltage phase grid control between the constant voltage control mode and the current limiting mode into the power angle switching conditions; The region division module is configured to: based on the power angle equation of the grid converter under the mixed current amplitude-voltage phase grid control in constant voltage control mode and current limiting mode, and combined with the power angle switching conditions, obtain the piecewise active power-power angle curve and unstable region. The boundary delineation module is configured to: obtain the analytical power angle range of the unstable region based on the boundary of the unstable operating region of the grid-connected converter under the mixed current amplitude-voltage phase grid control; The control module is configured to: eliminate all unstable regions by setting the lower limit of the current limiting coefficient of the ring current limiter under the premise of not compressing the original feasible region of the hybrid network control of current amplitude and voltage phase; wherein, the current limiting coefficient of the ring current limiter is introduced to scale the virtual internal potential amplitude to achieve current limiting.

[0008] Thirdly, the present invention provides an electronic device including a memory and a processor, and computer instructions stored in the memory and running on the processor, wherein the computer instructions, when executed by the processor, perform the method described in the first aspect.

[0009] Fourthly, the present invention provides a computer-readable storage medium for storing computer instructions, which, when executed by a processor, perform the method described in the first aspect.

[0010] The above one or more technical solutions have the following beneficial effects: This invention reveals the switching characteristics of hybrid current amplitude-voltage phase grid control between constant voltage control mode and current limiting mode, and determines the power angle operating range under constant voltage control mode and current limiting mode; it also reveals the fault recovery mechanism of grid converter under hybrid current amplitude-voltage phase grid control, determines the stable operating conditions of hybrid current amplitude-voltage phase grid control, and analyzes the power angle boundary of the stable operating region; by limiting the lower limit of the current limiting coefficient, the unstable region of hybrid current amplitude-voltage phase grid control is completely eliminated, ensuring the global fault recovery capability of grid converter.

[0011] In this invention, the lower limit of the current limiting coefficient is the virtual internal potential scaling factor corresponding to the formula for realizing virtual internal potential scaling under the premise of current amplitude-voltage phase hybrid grid control being exactly zero. This avoids instability due to continuous reduction caused by positive feedback, and enables the grid-type converter to maintain current limiting capability in the unstable region, greatly improving the fault recovery capability of the existing current amplitude-voltage phase hybrid grid control.

[0012] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0013] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0014] Figure 1 This is a flowchart of the fault recovery method for a hybrid grid converter with current amplitude and voltage phase in an embodiment of the present invention. Figure 2 This is a block diagram of a grid-connected single-unit grid-connected system of a grid-type converter in an embodiment of the present invention; Figure 3 This is a control block diagram illustrating the implicit implementation of CFM control in an embodiment of the present invention; Figure 4 This is the equivalent circuit of the grid-type converter using CFM control in the embodiments of the present invention; Figure 5 The diagram shows the segmented power angle curves and operating range of the unmodified CFM-controlled grid converter in this embodiment of the invention. Detailed Implementation

[0015] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0016] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.

[0017] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0018] Example 1 like Figure 1 As shown, this embodiment discloses a fault recovery method for a hybrid current amplitude-voltage phase grid converter, including: S1: The grid-type converter adopts CFM control, which uses the current limiting coefficient of the ring current limiter to scale the amplitude of the virtual internal potential, so that the grid-type converter can achieve accurate fault current limiting without changing the phase angle of the virtual internal potential.

[0019] like Figure 2 As shown, in step S1, the grid converter adopts droop control, which makes it exhibit voltage source characteristics through dual closed-loop control. The droop control equation is expressed as: (1) In the formula, d is the differential operator; t For time; i The phase difference between the grid-connected converter and the power grid; oh droop The angular frequency generated for droop control; K droop This is the droop control coefficient; P ref and P c These are the active power reference value and actual active power of the grid-type converter, respectively.

[0020] according to Figure 3 The implicit implementation control equations for CFM control are as follows: (2) In the formula, The current reference value provided for the outer voltage loop of the grid-type converter; Independently controllable gain; m This is the current limiting coefficient; U ref The reference voltage vector and magnitude at the grid connection point; U p The voltage at the common coupling point between the grid-connected converter and the power grid; X v is the virtual reactance; j is an imaginary number.

[0021] The current limiting coefficient generated by the ring current limiter m Its definition is as follows: (3) In the formula, I cmax This is the current threshold for a grid-type converter.

[0022] During a fault, the grid-connected inverter converter uses a ring current limiting device to limit the fault current. The specific current limiting strategy is as follows: (4) In the formula, This is the reference value for the actual input current in the inner current loop.

[0023] In current-limiting mode, CFM control adjusts the voltage phase angle generated by grid synchronization to... i Since the dynamic response of the current controller is much faster than that of the droop controller, it is assumed that... , This represents the actual output current of the grid-connected converter. Substituting equations (3) and (4) into equation (2), we obtain the equivalent circuit equation in the CLC as follows: (5) Therefore, the equivalent circuit under CFM control can be represented as having a virtual internal voltage. U v = kmU ref Voltage source and virtual internal reactance X v Series connection, such as Figure 4 As shown. Among them, l = km for U v Compared to U ref The scaling factor. Through the equivalent circuit, it can be obtained that CFM control can be achieved simply by scaling the virtual voltage source. U v While maintaining the amplitude, the power angle i Current limiting is achieved without changing the current.

[0024] S2: The current switching conditions of the CFM-controlled grid converter between constant voltage control (CVC) and current limiting control (CLC) are analyzed as power angle switching conditions.

[0025] In step S2, when the grid-type converter operates in CVC mode, it can be seen from equation (3) that the current limiting factor is... m =1, and because the current loop can always track the reference current generated by the CFM control. That is, satisfy Based on the above conditions and the equivalent circuit of CFM control, the switching condition from CVC to CLC mode can be obtained as follows: (6) In the formula, I c This refers to the actual current of the grid-type converter; U g and U g For the grid voltage vector and magnitude; U ref The reference voltage amplitude at the grid connection point; R g The equivalent resistance of the power grid; X g It is the equivalent reactance of the power grid.

[0026] Solving equation (6) yields the following range of power angles for switching from CVC to CLC mode: (7) In the formula, Θ represents the range of power angles when switching from CVC mode to CLC mode. The expression is as follows: (8) Therefore, a grid-type converter using CFM control can only switch from CVC mode to CLC mode if it satisfies equation (7).

[0027] In CLC mode, the output controlled by CFM is limited by a ring current limiter, that is: In this case, the voltage at the converter's point of common coupling (PCC) with the grid... U p It is expressed as follows: (9) Substituting equation (9) into equation (2), we get The expression is as follows: (10) Therefore, the switching condition from CLC mode to CVC mode can be obtained as follows: (11) The current limiting factor is satisfied at the critical switching point from CLC mode to CVC mode. m =1, therefore the range of power angles from CLC mode to CVC mode can be obtained as follows: (12) In the formula, Ω exitThe range of power angles for switching from CLC mode to CVC mode, where m Satisfy the following formula: (13) Due to the range of the work angle Θ and Ω exit They are complementary, thus ensuring smooth switching of CFM control and eliminating the problem of control mode oscillation.

[0028] S3: Derive the power angle equations of the grid-connected converter under CFM control in CVC and CLC, and perform fault recovery analysis on the grid-connected converter using CFM control.

[0029] In step S3, the grid-type converter using CFM control is equivalent to a voltage source connected in series with a constant virtual reactance. Therefore, the power angle equation for CVC mode can be obtained as follows: (14) In the formula, This refers to the active power in the CVC mode of a grid-type converter.

[0030] When a grid-type converter operates in CLC mode, CFM control can make the virtual internal voltage... U v The phase angle remains at i Since it remains unchanged, the power angle equation in CLC mode can be obtained as follows: (15) In the formula, This refers to the active power in the CLC mode of a grid-type converter.

[0031] It can be clearly seen that the virtual internal voltage in CLC mode U v It is not constant; it can be expressed as the work angle. i The function.

[0032] Due to output current I c The amplitude is limited to in CLC mode. I cmax We can obtain: (16) From equation (16), we can obtain U v Regarding the angle of attack i function U v ( i The function expression is as follows: (17) S4: Derive the boundary of the unstable operating region of the grid converter under CFM control, and obtain the analytical power angle range of the unstable region.

[0033] In step S4, as shown in equation (17), the prerequisite for CFM control to achieve virtual internal potential scaling is: (18) By solving equation (18), the stable power angle range of the grid-type converter using CFM control can be obtained as follows: (19) In the formula, Θ s For the stable region using CFM control, where n The expression is as follows: (20) By using equations (14) and (15) with the range of the work angle Θ, Ω exit and Θ s This allows us to obtain piecewise active-work angle curves and unstable regions, thus enabling precise quantification of their transient stability margin.

[0034] S5: Set the lower limit of the current limiting coefficient to eliminate all unstable regions without compressing the original feasible region of CFM control, and ensure the global fault recovery capability of the grid converter.

[0035] In step S5, it can be seen from equation (19) that when the work angle i Within the range of work angle Θ s At that time, the grid-type converter can operate stably. If i Within the range of work angle Θ s When the voltage is outside the range, the grid converter cannot limit current by scaling the virtual internal potential amplitude, thus losing its current limiting capability, and the current limiting coefficient is also reduced. m It will continue to shrink, triggering positive feedback. Therefore, in Figure 5 In the middle, as long as the current limiting coefficient is... m Limiting the lower limit prevents it from decreasing continuously due to positive feedback and becoming unstable. This allows the grid-type converter to maintain current limiting capability in unstable regions, greatly improving the fault recovery capability of existing CFM control.

[0036] Among them, regarding the current limiting coefficient m lower limit m min The solution needs to be quite accurate: if m min Setting it too high will increase the rate limiting factor. m Prematurely entering saturation reduces the normal operating range of CFM control; if m minIf the current limiting coefficient is set too low, the CFM control will be unable to restore its current limiting capability in a timely manner. Therefore, the chosen current limiting coefficient... m lower limit m min It should be the virtual internal potential scaling factor corresponding to when equation (18) is exactly zero, i.e. (twenty one) In the formula, m min That is, the current limiting factor. m The lower limit.

[0037] This eliminates all unstable regions in the existing CFM control and enhances the fault recovery capability of the grid converter.

[0038] This embodiment reveals the switching characteristics of CFM control between CVC and CLC modes, and determines the operating range of the power angle in CVC and CLC modes.

[0039] This embodiment reveals the fault recovery mechanism of grid-connected converters under CFM control, determines the stable operating conditions of CFM control, and analyzes the power angle boundary of the stable operating region.

[0040] This embodiment proposes an improved CFM control method. By limiting the lower limit of the current limiting coefficient μ, the unstable region of CFM control is completely eliminated, ensuring the global fault recovery capability of the grid converter.

[0041] Example 2 The purpose of this embodiment is to provide a fault recovery method for a grid converter with a hybrid current amplitude and voltage phase configuration, including: The analysis module is configured to: analyze the current switching conditions of the grid-type converter under the mixed current amplitude-voltage phase grid control between the constant voltage control mode and the current limiting mode into the power angle switching conditions; The region division module is configured to: based on the power angle equation of the grid converter under the mixed current amplitude-voltage phase grid control in constant voltage control mode and current limiting mode, and combined with the power angle switching conditions, obtain the piecewise active power-power angle curve and unstable region. The boundary delineation module is configured to: obtain the analytical power angle range of the unstable region based on the boundary of the unstable operating region of the grid-connected converter under the mixed current amplitude-voltage phase grid control; The control module is configured to: eliminate all unstable regions by setting the lower limit of the current limiting coefficient of the ring current limiter under the premise of not compressing the original feasible region of the hybrid network control of current amplitude and voltage phase; wherein, the current limiting coefficient of the ring current limiter is introduced to scale the virtual internal potential amplitude to achieve current limiting.

[0042] In further embodiments, the following is also provided: An electronic device includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor. When executed by the processor, the computer instructions perform the method described in Embodiment 1. For brevity, further details are omitted here.

[0043] It should be understood that in this embodiment, the processor can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor, etc.

[0044] Memory may include read-only memory and random access memory, and provides instructions and data to the processor. A portion of memory may also include non-volatile random access memory. For example, memory may also store information about the device type.

[0045] A computer-readable storage medium for storing computer instructions, which, when executed by a processor, perform the method described in Embodiment 1.

[0046] The method in Embodiment 1 can be directly implemented by a hardware processor, or implemented by a combination of hardware and software modules within the processor. The software modules can reside in readily available storage media in the art, such as random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, or registers. This storage medium is located in memory; the processor reads information from the memory and, in conjunction with its hardware, completes the steps of the above method. To avoid repetition, a detailed description is not provided here.

[0047] A computer program product includes a computer program that, when executed by a processor, implements the method described in Embodiment 1.

[0048] The present invention also provides at least one computer program product tangibly stored on a non-transitory computer-readable storage medium. The computer program product includes computer-executable instructions, such as instructions included in program modules, which execute in a device on a target real or virtual processor to perform the processes / methods described above. Typically, program modules include routines, programs, libraries, objects, classes, components, data structures, etc., that perform specific tasks or implement specific abstract data types. In various embodiments, the functionality of program modules can be combined or divided among program modules as needed. The machine-executable instructions for the program modules can execute within a local or distributed device. In a distributed device, the program modules can reside in both local and remote storage media.

[0049] The computer program code used to implement the methods of the present invention may be written in one or more programming languages. This computer program code may be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device, such that when executed by the computer or other programmable data processing device, the program code causes the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may be executed entirely on a computer, partially on a computer, as a stand-alone software package, partially on a computer and partially on a remote computer, or entirely on a remote computer or server.

[0050] In the context of this invention, computer program code or related data may be carried by any suitable carrier to enable a device, apparatus, or processor to perform the various processes and operations described above. Examples of carriers include signals, computer-readable media, and the like. Examples of signals may include electrical, optical, radio, sound, or other forms of propagation signals, such as carrier waves, infrared signals, etc.

[0051] Those skilled in the art will recognize that the units and algorithm steps described in conjunction with the embodiments herein can be implemented in electronic hardware or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0052] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A fault recovery method for a current amplitude-voltage phase hybrid grid converter, characterized in that, include: The current switching condition of the grid-type converter under the mixed current amplitude-voltage phase grid control between the constant voltage control mode and the current limiting mode is analyzed as the power angle switching condition. A grid-connected converter is equivalent to having a virtual internal voltage. U v Voltage source and virtual internal reactance X v By introducing a ring current limiter with a current limiting coefficient μ, the amplitude of the voltage source is scaled while the power angle remains constant, thus achieving current limiting. The switching condition from constant voltage control mode to current limiting mode is as follows: In the formula, I c This refers to the actual current of the grid-type converter. For grid voltage vector, U g The voltage amplitude of the power grid. U ref The reference voltage amplitude at the grid connection point. R g The equivalent resistance of the power grid. X g I is the equivalent reactance of the power grid. cmax The current threshold of the grid-type converter. θ The phase difference between the grid-connected converter and the power grid, For independent control of gain, This is the current reference vector output from the outer voltage loop; The power angle range Θ for switching from constant voltage control mode to current limiting mode is: ； ； in, k It is an integer. It is a set of integers; The switching condition from current limiting mode to constant voltage control mode is: The power angle range (Ω) for switching from current limiting mode to constant voltage control mode exit for: ； Based on the power angle equations of the grid-connected converter in constant voltage control mode and current limiting mode, and combined with the power angle switching conditions, the piecewise active power-power angle curves and unstable regions are obtained, specifically: Based on the power angle equations of the grid-connected converter in constant voltage control mode and current limiting mode, the premise for realizing virtual internal potential scaling is obtained, and then the stable power angle range of the grid-connected converter is obtained; combined with the power angle switching conditions between constant voltage control mode and current limiting mode, the piecewise active power-power angle curves and unstable regions are obtained. Based on the boundary of the unstable region of the grid converter, the analytical power angle range of the unstable region is obtained; Considering the premise of not compressing the original feasible region of the mixed current amplitude-voltage phase network control, the lower limit of the current limiting coefficient of the ring current limiter is tuned to eliminate all unstable regions; The premise for the virtual internal potential scaling is: Stable power angle range of grid converter Θ s for: ； ； The selected current limiting coefficient μ lower limit μ min It should be the virtual internal potential scaling factor that corresponds to the condition that the virtual internal potential scaling inequality is zero, i.e. 。 2. The fault recovery method for a hybrid current amplitude-voltage phase grid converter as described in claim 1, characterized in that, The power angle equation for a grid-connected converter in constant voltage control mode is: ； in, The active power in CVC mode of a grid-type converter; The power angle equation for a grid-connected converter in current-limiting mode is: ； in, This refers to the active power in the CLC mode of a grid-type converter.

3. A fault recovery system for a current amplitude-voltage phase hybrid grid converter, employing the fault recovery method for current amplitude-voltage phase hybrid grid converters as described in any one of claims 1-2, characterized in that, include: The parsing module is configured to: parse the current switching conditions of the grid-type converter between constant voltage control mode and current limiting mode into power angle switching conditions; The region division module is configured to: obtain the segmented active power-power angle curve and unstable region based on the power angle equation of the grid converter in constant voltage control mode and current limiting mode, combined with the power angle switching condition. The boundary delineation module is configured to: obtain the analytical power angle range of the unstable region based on the boundary of the unstable operating region of the grid converter; The control module is configured to: eliminate all unstable regions by setting the lower limit of the current limiting coefficient of the ring current limiter under the premise of not compressing the original feasible region of the hybrid network control of current amplitude and voltage phase; wherein, the current limiting coefficient of the ring current limiter is introduced to scale the virtual internal potential amplitude to achieve current limiting.

4. An electronic device, characterized in that, It includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor, which, when executed by the processor, perform the method according to any one of claims 1-2.

5. A computer-readable storage medium, characterized in that, Used to store computer instructions, which, when executed by a processor, perform the method described in any one of claims 1-2.

Images