A current reference current limiting method, system, device, and storage medium with equivalent reactance characteristics.

Abstract

This invention relates to the field of converter control, specifically to a current reference current limiting method, system, device, and storage medium with equivalent reactance characteristics. The method involves: acquiring the original current reference and maximum allowable output current amplitude of a grid-connected GFM converter; calculating the original phase angle and original amplitude based on the original current reference; calculating the amplitude reduction ratio based on the original amplitude and maximum allowable output current amplitude; calculating the current reference rotation angle based on the amplitude reduction ratio; calculating the phase angle of the current reference after limiting based on the original phase angle and current reference rotation angle; calculating the amplitude of the current reference after limiting based on the original amplitude and amplitude reduction ratio; and generating the current reference after limiting based on the phase angle and amplitude. This invention overcomes the shortcomings of existing current reference current limiting methods that cannot achieve an equivalent output impedance with reactance characteristics after the grid-connected GFM converter enters current limiting mode, significantly improving the transient stability margin of the system.

Description

Technical Field

[0001] This invention relates to the field of converter control, and more specifically to a current reference current limiting method, system, device, and storage medium with equivalent reactance characteristics. Background Technology

[0002] Grid-Forming (GFM) converters are key equipment for integrating high proportions of renewable energy into the power grid. By directly regulating port voltage and frequency, GFM converters can provide support for the power grid. Unlike synchronous generators, which can withstand large overcurrents for short periods, the semiconductor devices in converters have limited overcurrent capacity. Under conditions such as voltage dips, short circuits, and phase disturbances, current limiting methods must be configured to protect the devices and prevent the converter from disconnecting from the grid.

[0003] Existing current limiting methods mainly include two technical approaches. The first is the virtual impedance current limiting method, which suppresses the converter's output current by adjusting the equivalent output impedance of the grid-connected GFM converter. However, this method requires prior estimation of the magnitude of external disturbances to achieve a good current limiting effect. When the external disturbance exceeds the design threshold of this method, the current limiting effect cannot be maintained, posing a risk to the safe operation of the converter. The second current limiting method is the current reference current limiting method. This method directly constrains the amplitude of the current reference of the grid-connected GFM converter and implements the constrained current reference through fast-response current control, thereby ensuring that the converter's output current can always be maintained within the safe threshold range, ensuring the safe operation of the grid-connected GFM converter.

[0004] However, existing current-referenced current limiting methods, including priority-based current-limiting methods and magnitude current-limiting methods, often lead to grid-connected GFM converters failing to resume normal operation after current limiting is triggered. Furthermore, their equivalent output impedance exhibits resistive characteristics, reducing the transient stability margin of the grid-connected GFM converter and compromising its ability to regulate output power during grid disturbances. In addition, existing grid relay protection devices often require power generation equipment, including grid-connected GFM converters, to exhibit primarily reactive characteristics in their equivalent output impedance during large grid disturbances, a requirement that existing current-referenced current limiting methods cannot meet. Summary of the Invention

[0005] To address the problems mentioned in the prior art, this invention proposes a current reference current limiting method, system, device, and storage medium with equivalent reactance characteristics. This solves the shortcomings of existing current reference current limiting methods that cannot achieve equivalent output impedance with reactance characteristics after the grid-type GFM converter enters current limiting mode. It significantly improves the transient stability margin of the system and meets the requirements of power grid relay protection devices for the equivalent output impedance of power generation equipment.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: The present invention proposes a current reference current limiting method with equivalent reactance characteristics, applied to a grid-type GFM converter, comprising the following steps: S1. Obtain the original current reference and the maximum allowable output current amplitude of the grid-type GFM converter; S2. Based on the original current reference, the original phase angle and original amplitude are calculated; S3. Calculate the amplitude reduction ratio based on the original amplitude and the maximum allowable output current amplitude; S4. Calculate the current reference rotation angle based on the amplitude reduction ratio; S5. Based on the original phase angle and the current reference rotation angle, calculate the phase angle of the current reference after limiting; and based on the original amplitude and the amplitude reduction ratio, calculate the amplitude of the current reference after limiting. S6. Based on the phase angle and amplitude of the current reference after limiting, generate the current reference after limiting to the current controller so that the equivalent output impedance of the grid-type GFM converter exhibits reactance characteristics under current limiting state.

[0007] As a further improvement to the present invention, the original phase angle in S2 is:

[0008] In the formula: The original phase angle; It is a two-parameter arctangent function; , These represent the current reference on the horizontal axis and the current reference on the vertical axis in the stationary or rotating coordinate system of the original current reference, respectively. The formula for calculating the original amplitude in S2 is as follows:

[0009] In the formula: This is the original amplitude.

[0010] As a further improvement to the present invention, the formula for calculating the amplitude reduction ratio in S3 is as follows:

[0011] In the formula: The amplitude reduction ratio; The function is for finding the minimum value; This represents the maximum permissible output current amplitude.

[0012] As a further improvement to the present invention, the calculation of the current reference rotation angle in S4 is as follows:

[0013] In the formula: The rotation angle is the reference angle for the current. It is an inverse cosine function.

[0014] As a further improvement of the present invention, the formula for calculating the phase angle of the current reference after limiting in S5 is as follows:

[0015] In the formula: The phase angle used as the reference for the current after limiting; The formula for calculating the amplitude of the current reference after limiting in S5 is as follows:

[0016] In the formula: This is the reference amplitude of the current after limiting.

[0017] As a further improvement of the present invention, the calculation formula for the current reference after limiting in S6 is as follows:

[0018]

[0019] In the formula: The current reference after limiting is represented on the horizontal axis in a stationary or rotating coordinate system; This represents the current reference after limiting the vertical axis in a stationary or rotating coordinate system.

[0020] As a further improvement of the present invention, the voltage control of the grid-type GFM converter adopts a vector voltage control method with grid-side current feedforward; When the grid-type GFM converter enters the current-limiting state, the state of the integral controller or resonant controller in the voltage control is set to zero or frozen.

[0021] This invention proposes a current reference current limiting system with equivalent reactance characteristics, comprising: The voltage control module is used to obtain the original current reference and the maximum allowable output current amplitude of the grid-type GFM converter; The current reference current limiting module is used to calculate the original phase angle and original amplitude based on the original current reference. Used to calculate the amplitude reduction ratio based on the original amplitude and the maximum allowable output current amplitude; used to calculate the current reference rotation angle based on the amplitude reduction ratio; used to calculate the phase angle of the current reference after limiting based on the original phase angle and the current reference rotation angle; used to calculate the amplitude of the current reference after limiting based on the original amplitude and the amplitude reduction ratio; used to generate the current reference after limiting to the current controller based on the phase angle and amplitude of the current reference after limiting. The current control module is used to make the equivalent output impedance of the grid-type GFM converter exhibit reactive characteristics under current-limited conditions, based on the current reference after current limiting.

[0022] This invention proposes a current reference current limiting device with equivalent reactance characteristics, comprising a processor and a memory, wherein the processor executes a computer program stored in the memory to implement the current reference current limiting method with equivalent reactance characteristics as described above.

[0023] The present invention proposes a computer-readable storage medium for storing a computer program, wherein the computer program, when executed by a processor, implements the current reference current limiting method with equivalent reactance characteristics as described above.

[0024] Compared with the prior art, the present invention achieves the following technical effects: This invention, while effectively limiting the output current amplitude of a grid-connected GFM converter, introduces a current reference phase rotation mechanism based on the amplitude reduction ratio. This allows the converter's equivalent output impedance to actively exhibit reactance characteristics after current limiting is triggered by grid disturbances, significantly improving the transient stability margin of the grid-connected GFM converter during faults, effectively avoiding the risk of reverse power absorption, and ensuring the converter's continuous grid-connected operation capability under harsh grid conditions. Furthermore, this method enables the converter's impedance characteristics to actively meet the basic requirements of grid relay protection devices for power generation equipment, enhancing the grid's compatibility and support capabilities, and providing a foundation for the safe and stable operation of the power system. Finally, this invention achieves overcurrent protection for the grid-connected GFM converter under grid disturbances by directly adjusting the current reference and leveraging the fast response characteristics of current control. Attached Figure Description

[0025] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a schematic diagram of the method of the present invention; Figure 3 This is a comparison diagram of the potential difference between the internal potential of the converter and the terminal voltage after a 90-degree lag, and the output current of the converter. Figure 4 This is a comparison diagram of the active power response between the current reference current limiting method proposed in this invention and existing methods; Figure 5 This is a control diagram of the system of the present invention. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0027] See Figure 1 and Figure 2 This embodiment proposes a current reference current limiting method with equivalent reactance characteristics, applied to a grid-type GFM converter, including the following steps: S1. Obtain the original current reference and the maximum allowable output current amplitude of the grid-type GFM converter; S2. Based on the original current reference, the original phase angle and original amplitude are calculated; S3. Calculate the amplitude reduction ratio based on the original amplitude and the maximum allowable output current amplitude; S4. Calculate the current reference rotation angle based on the amplitude reduction ratio; S5. Based on the original phase angle and the current reference rotation angle, calculate the phase angle of the current reference after limiting; and based on the original amplitude and the amplitude reduction ratio, calculate the amplitude of the current reference after limiting. S6. Based on the phase angle and amplitude of the current reference after limiting, generate the current reference after limiting to the current controller so that the equivalent output impedance of the grid-type GFM converter exhibits reactance characteristics under current limiting state.

[0028] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments: like Figure 1 and Figure 2 As shown, the specific implementation method of the current reference current limiting method with equivalent reactance characteristics proposed in this invention is as follows: First, obtain the raw current reference provided by the voltage control, including... and ,in The current reference on the horizontal axis in a stationary or rotating coordinate system. This represents the current reference along the vertical axis in a stationary or rotating coordinate system.

[0029] Maximum current amplitude. Used to provide a converter current amplitude limit for the current reference current limiting. ,in This indicates the maximum permissible output current amplitude of the grid-type GFM converter.

[0030] Original current reference phase angle extraction. The phase angle used to calculate the original current reference. The specific calculation is as follows:

[0031] In the formula: The original phase angle; It is a two-parameter arctangent function.

[0032] Calculation of the original current reference amplitude. This is used to calculate the amplitude of the original current reference. The specific calculation is as follows:

[0033] In the formula: This is the original amplitude.

[0034] Amplitude reduction ratio calculation. This is used to calculate the reduction ratio of the current reference amplitude. The specific calculation is as follows:

[0035] In the formula: The amplitude reduction ratio; The function is for finding the minimum value; This represents the maximum permissible output current amplitude.

[0036] Current reference rotation angle calculation. This is the rotation angle used to calculate the original current reference phase angle required to generate the equivalent output reactance. The specific calculation is as follows:

[0037] In the formula: The rotation angle is the reference angle for the current. This is an inverse cosine function. An adder is used to calculate the phase angle of the current reference after limiting. The specific calculation is as follows:

[0038] In the formula: This is the reference phase angle for the current after limiting.

[0039] Multiplier. Used to calculate the amplitude of the current reference after limiting. The specific calculation is as follows:

[0040] In the formula: This is the reference amplitude of the current after limiting.

[0041] Current reference generation after limiting. Used to calculate the current reference after limiting and provided to current control to achieve the current limiting function of the grid-connected GFM converter. The specific calculation is as follows:

[0042]

[0043] In the formula: The current reference after limiting is represented on the horizontal axis in a stationary or rotating coordinate system; This represents the current reference after limiting the vertical axis in a stationary or rotating coordinate system.

[0044] Current reference after limiting. Generated current reference. and This will be provided to the current control to achieve the output current limit of the grid-type GFM converter.

[0045] like Figure 3 The figure shows a comparison between the potential difference between the internal potential and the terminal voltage of the grid-type GFM converter after a 90-degree lag, and the converter output current, when the grid voltage drops to 0.5 times the per-unit value in 0.1 seconds using the proposed current reference current limiting method. The figure shows that when the grid voltage does not drop, the voltage difference between the internal potential and the terminal voltage is 0, meaning the equivalent output impedance of the grid-type GFM converter is 0. However, when the grid voltage drops after 0.1 seconds, the potential difference lagging by 90 degrees is in phase with the output current, meaning the actual potential difference leads the output current by 90 degrees. Therefore, the equivalent output impedance exhibits reactance characteristics. Furthermore, from... Figure 3 The response of the output current shows that when the mains voltage drops, the output current can be well limited to within 1.2 times the per-unit value of the preset maximum allowable current.

[0046] Figure 4 This study compares the active power response of the proposed current reference current limiting method with existing methods when the grid voltage drops to 0.5 times the per-unit value for 0.75 seconds. Figure 4 As shown in the attached diagram, the existing current reference current limiting method requires approximately 1.25 seconds for active power to return to its normal operating point after fault clearance. Furthermore, grid-connected GFM converters absorb active power from the grid, which can easily trigger their reverse power protection, affecting the safe operation of the converter. In contrast, from... Figure 4 As can be seen in the accompanying figures below, the current reference current limiting method proposed in this invention can restore its normal operating state in about 0.75 seconds under test conditions, and avoids the problem of power reversal.

[0047] It should be particularly noted in this embodiment that: In this embodiment, voltage control needs to employ a vector voltage control method with grid-side current feedforward.

[0048] In this embodiment, when external interference causes the grid-type GFM converter to enter current limiting mode, the integral control or resonant control in the voltage control should be set to zero or frozen to prevent the integral control or resonant control from saturating.

[0049] The current reference current limiting method proposed in this invention requires high-bandwidth current control to ensure the accurate realization of the current reference after limiting.

[0050] Based on the same inventive concept, this embodiment of the invention also provides a current reference current limiting system with equivalent reactance characteristics. Since the principle of solving the problem by this current reference current limiting system with equivalent reactance characteristics is similar to that of the aforementioned current reference current limiting method with equivalent reactance characteristics, the implementation of this current reference current limiting system with equivalent reactance characteristics can refer to the implementation of the current reference current limiting method with equivalent reactance characteristics, and the repeated parts will not be described again.

[0051] In specific implementation, the current reference current limiting system with equivalent reactance characteristics provided in this embodiment of the invention specifically includes: The voltage control module is used to obtain the original current reference and the maximum allowable output current amplitude of the grid-type GFM converter; The current reference current limiting module is used to calculate the original phase angle and original amplitude based on the original current reference. Used to calculate the amplitude reduction ratio based on the original amplitude and the maximum allowable output current amplitude; used to calculate the current reference rotation angle based on the amplitude reduction ratio; used to calculate the phase angle of the current reference after limiting based on the original phase angle and the current reference rotation angle; used to calculate the amplitude of the current reference after limiting based on the original amplitude and the amplitude reduction ratio; used to generate the current reference after limiting to the current controller based on the phase angle and amplitude of the current reference after limiting. The current control module is used to make the equivalent output impedance of the grid-type GFM converter exhibit reactive characteristics under current-limited conditions, based on the current reference after current limiting.

[0052] See Figure 5 The system in this embodiment includes: Power control module: used to generate voltage and frequency references for grid-connected GFM converters to enable the converters to support the voltage and frequency of the power grid; Voltage control module: used to generate voltage and frequency references for power control and provide the original current reference for the converter; Current reference current limiting module: used to limit the amplitude and adjust the angle of the original current reference provided by the voltage control to prevent the voltage control from providing an excessive current reference, which would affect the safe operation of the converter. Current control: used to implement the current reference after limiting and to generate the pulse-width modulation (PWM) voltage reference for the grid-type GFM converter; Grid-connected GFM converter: used to connect new energy sources to the grid and convert the pulse width modulation (PWM) voltage reference into actual three-phase voltage output.

[0053] Accordingly, embodiments of the present invention also provide a current reference current limiting device with equivalent reactance characteristics, including a processor and a memory, wherein the processor executes a computer program stored in the memory to implement the current reference current limiting method with equivalent reactance characteristics as provided in embodiments of the present invention.

[0054] For more detailed information on the above methods, please refer to the relevant content disclosed in the foregoing embodiments, which will not be repeated here.

[0055] Accordingly, embodiments of the present invention also provide a computer-readable storage medium for storing a computer program, wherein the computer program, when executed by a processor, implements the current reference current limiting method with equivalent reactance characteristics as described above in embodiments of the present invention.

[0056] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems, devices, and storage media disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0057] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. 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.

[0058] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly by hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0059] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0060] The present invention has provided a detailed description of the current reference current limiting method, system, device, and storage medium with equivalent reactance characteristics. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A current reference current limiting method with equivalent reactance characteristics, applied to a grid-type GFM converter, characterized in that, Includes the following steps: S1. Obtain the original current reference and the maximum allowable output current amplitude of the grid-type GFM converter; S2. Based on the original current reference, the original phase angle and original amplitude are calculated; the formula for calculating the original phase angle is: In the formula: The original phase angle; It is a two-parameter arctangent function; , These represent the current reference on the horizontal axis and the current reference on the vertical axis in the stationary or rotating coordinate system of the original current reference, respectively. The formula for calculating the original amplitude is as follows: In the formula: This is the original amplitude. S3. Calculate the amplitude reduction ratio based on the original amplitude and the maximum allowable output current amplitude; the formula for calculating the amplitude reduction ratio is as follows: In the formula: The amplitude reduction ratio; The function is for finding the minimum value; This is the maximum allowable output current amplitude; S4. Calculate the current reference rotation angle based on the amplitude reduction ratio; the current reference rotation angle is calculated as follows: In the formula: The rotation angle is the reference angle for the current. It is the inverse cosine function; S5. Based on the original phase angle and the current reference rotation angle, calculate the phase angle of the current reference after limiting; and based on the original amplitude and the amplitude reduction ratio, calculate the amplitude of the current reference after limiting. S6. Generate the current reference after limiting based on the phase angle and amplitude of the current reference after limiting; The current reference after limiting is input to the current controller so that the equivalent output impedance of the grid-type GFM converter exhibits reactance characteristics under current limiting conditions.

2. The current reference current limiting method with equivalent reactance characteristics according to claim 1, characterized in that, The formula for calculating the phase angle of the current reference after limiting in S5 is as follows: In the formula: The phase angle used as the reference for the current after limiting; The formula for calculating the amplitude of the current reference after limiting in S5 is as follows: In the formula: This is the reference amplitude of the current after limiting.

3. The current reference current limiting method with equivalent reactance characteristics according to claim 1, characterized in that, The calculation formula for the current reference after limiting in S6 is as follows: In the formula: The current reference after limiting is represented on the horizontal axis in a stationary or rotating coordinate system; This represents the current reference after limiting the vertical axis in a stationary or rotating coordinate system.

4. The current reference current limiting method with equivalent reactance characteristics according to claim 1, characterized in that, The voltage control of the grid-type GFM converter adopts a vector voltage control method with grid-side current feedforward. When the grid-type GFM converter enters the current-limiting state, the state of the integral controller or resonant controller in the voltage control is set to zero or frozen.

5. A current reference current limiting system with equivalent reactance characteristics, characterized in that, include: The voltage control module is used to obtain the original current reference and the maximum allowable output current amplitude of the grid-type GFM converter; The current reference current limiting module is used to calculate the original phase angle and original amplitude based on the original current reference; the formula for calculating the original phase angle is: In the formula: The original phase angle; It is a two-parameter arctangent function; , These represent the current reference on the horizontal axis and the current reference on the vertical axis in the stationary or rotating coordinate system of the original current reference, respectively. The formula for calculating the original amplitude is as follows: In the formula: This is the original amplitude. Used to calculate the amplitude reduction ratio based on the original amplitude and the maximum allowable output current amplitude; The formula for calculating the amplitude reduction ratio is as follows: In the formula: The amplitude reduction ratio; The function is for finding the minimum value; This is the maximum allowable output current amplitude; Used to calculate the current reference rotation angle based on the amplitude reduction ratio; the current reference rotation angle is calculated as follows: In the formula: The rotation angle is the reference angle for the current. It is the inverse cosine function; Used to calculate the phase angle of the current reference after limiting, based on the original phase angle and the current reference rotation angle; Used to calculate the amplitude of the current reference after limiting based on the original amplitude and the amplitude reduction ratio; used to generate the current reference after limiting based on the phase angle and amplitude of the current reference after limiting. Input the current reference after limiting to the current controller; The current control module is used to make the equivalent output impedance of the grid-type GFM converter exhibit reactive characteristics under current-limited conditions, based on the current reference after current limiting.

6. A current reference current limiting device with equivalent reactance characteristics, characterized in that, It includes a processor and a memory, wherein the processor executes a computer program stored in the memory to implement the current reference current limiting method with equivalent reactance characteristics as described in any one of claims 1 to 4.

7. A computer-readable storage medium, characterized in that, Used to store a computer program, wherein the computer program, when executed by a processor, implements the current reference current limiting method with equivalent reactance characteristics as described in any one of claims 1 to 4.

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