Control method of power converter and related device

Abstract

The application provides a control method of a power converter and a related device, and relates to the technical field of power conversion. The control method of the power converter comprises the following steps: adjusting positive sequence virtual impedance within a positive sequence amplitude limiting range according to positive sequence current output by the power converter; and / or adjusting negative sequence virtual impedance within a negative sequence amplitude limiting range according to negative sequence current output by the power converter; and controlling the power converter according to the positive sequence virtual impedance and / or the negative sequence virtual impedance. According to the application, the virtual impedance is adjusted according to the current output by the power converter, and the virtual impedance is limited, so that the virtual impedance is always kept in a safe range, thereby realizing the current limiting function of the power converter and improving the transient stability of the power conversion system.

Description

Technical Field

[0001] This application relates to the field of power conversion technology, specifically to a control method and related apparatus for a power converter. Background Technology

[0002] In power converter applications, when the grid voltage drops, the voltage difference between the power converter's output voltage and the grid voltage suddenly increases, causing the power converter's output current to rise rapidly. Therefore, current limiting measures are needed to protect the normal operation of the power converter.

[0003] The relevant current limiting measures have a significant impact on the stability of the power conversion system, especially when the grid voltage experiences an asymmetrical drop, which may cause transient instability in the power conversion system. Summary of the Invention

[0004] This application provides a control method and related apparatus for a power converter, which improves the transient stability of the power conversion system while realizing the current limiting function of the power converter.

[0005] In a first aspect, embodiments of this application provide a control method for a power converter, the control method comprising: adjusting a positive-sequence virtual impedance within a positive-sequence limiting range based on a positive-sequence current output by the power converter; and / or adjusting a negative-sequence virtual impedance within a negative-sequence limiting range based on a negative-sequence current output by the power converter; and controlling the power converter based on the positive-sequence virtual impedance and / or the negative-sequence virtual impedance.

[0006] Optionally, adjusting the positive-sequence virtual impedance within the positive-sequence limiting range based on the positive-sequence current output by the power converter includes: generating a positive-sequence adjustment signal based on the difference between the amplitude of the positive-sequence current output by the power converter and a preset positive-sequence current threshold; performing amplitude limiting processing on the positive-sequence adjustment signal to generate a positive-sequence limiting signal; and generating a positive-sequence virtual impedance based on the positive-sequence limiting signal.

[0007] Optionally, the step of limiting the positive sequence adjustment signal to generate a positive sequence limiting signal includes: comparing the positive sequence adjustment signal with a positive sequence lower limit amplitude value and a positive sequence upper limit amplitude value, wherein the positive sequence lower limit amplitude value is a preset value, and the positive sequence upper limit amplitude value is generated based on the positive sequence current output by the power converter; in response to the positive sequence adjustment signal being less than the positive sequence lower limit amplitude value, using the positive sequence lower limit amplitude value as the positive sequence limiting signal; or, in response to the positive sequence adjustment signal being greater than the positive sequence upper limit amplitude value, using the positive sequence upper limit amplitude value as the positive sequence limiting signal; or, in response to the positive sequence adjustment signal being between the positive sequence lower limit amplitude value and the positive sequence upper limit amplitude value, using the positive sequence adjustment signal as the positive sequence limiting signal.

[0008] Optionally, the positive sequence upper limit amplitude is obtained by multiplying the positive sequence characterization factor by a preset positive sequence upper limit reference value, wherein the positive sequence characterization factor is generated based on the difference between the amplitude of the positive sequence current and a preset positive sequence current threshold.

[0009] Optionally, the positive sequence characterization factor is generated based on the difference between the amplitude of the positive sequence current and a preset positive sequence current threshold, including: the difference between the amplitude of the positive sequence current and the preset positive sequence current threshold is processed by high-pass filtering, scaling, limiting and offset processing to generate the positive sequence characterization factor.

[0010] Optionally, the lower limit of the positive sequence amplitude is 0.

[0011] Optionally, generating a positive-sequence virtual impedance based on the positive-sequence limiting signal includes: using the positive-sequence limiting signal as a positive-sequence virtual resistance, and using the product of the positive-sequence virtual resistance and a preset positive-sequence impedance coefficient as a positive-sequence virtual reactance.

[0012] Optionally, adjusting the negative-sequence virtual impedance within the negative-sequence limiting range based on the negative-sequence current output by the power converter includes: generating a negative-sequence adjustment signal based on the difference between the amplitude of the negative-sequence current output by the power converter and a preset negative-sequence current threshold; performing amplitude limiting processing on the negative-sequence adjustment signal to generate a negative-sequence limiting signal; and generating a negative-sequence virtual impedance based on the negative-sequence limiting signal.

[0013] Optionally, the step of limiting the negative-sequence adjustment signal to generate a negative-sequence limiting signal includes: comparing the negative-sequence adjustment signal with a negative-sequence lower limit amplitude value and a negative-sequence upper limit amplitude value, wherein the negative-sequence lower limit amplitude value is a preset value, and the negative-sequence upper limit amplitude value is generated based on the positive-sequence current and negative-sequence current output by the power converter; in response to the negative-sequence adjustment signal being less than the negative-sequence lower limit amplitude value, using the negative-sequence lower limit amplitude value as the negative-sequence limiting signal; or, in response to the negative-sequence adjustment signal being greater than the negative-sequence upper limit amplitude value, using the negative-sequence upper limit amplitude value as the negative-sequence limiting signal; or, in response to the negative-sequence adjustment signal being between the negative-sequence lower limit amplitude value and the negative-sequence upper limit amplitude value, using the negative-sequence adjustment signal as the negative-sequence limiting signal.

[0014] Optionally, the negative sequence upper limit amplitude is obtained by multiplying the negative sequence characterization factor by a preset negative sequence upper limit benchmark value, wherein the negative sequence characterization factor is generated based on the amplitude of the negative sequence current, the amplitude of the positive sequence current, and a preset positive sequence current threshold.

[0015] Optionally, the negative sequence characterization factor is generated based on the amplitude of the negative sequence current, the amplitude of the positive sequence current, and a preset positive sequence current threshold. The generation process includes: the difference between the amplitude of the positive sequence current and the preset positive sequence current threshold is high-pass filtered, squared, and summed with the square of the amplitude of the negative sequence current. Then, the negative sequence characterization factor is generated through scaling, limiting, and offset processing.

[0016] Optionally, the negative order lower limit amplitude value is 0.

[0017] Optionally, generating a negative-sequence virtual impedance based on the negative-sequence limiting signal includes: using the negative-sequence limiting signal as a negative-sequence virtual resistance, and using the product of the negative-sequence virtual resistance and a preset negative-sequence impedance coefficient as a negative-sequence virtual reactance.

[0018] Optionally, the control method further includes: taking the difference between a preset positive-sequence reference voltage and the positive-sequence voltage output by the power converter and the voltage obtained by multiplying the positive-sequence current and the positive-sequence virtual impedance to generate a positive-sequence voltage error signal; performing voltage loop adjustment on the positive-sequence voltage error signal to generate a positive-sequence voltage control signal; and controlling the power converter according to the positive-sequence voltage control signal.

[0019] Optionally, the control method further includes: taking the difference between a preset negative-sequence reference voltage and the negative-sequence voltage output by the power converter and the voltage obtained by multiplying the negative-sequence current and the negative-sequence virtual impedance to generate a negative-sequence voltage error signal; performing voltage loop adjustment on the negative-sequence voltage error signal to generate a negative-sequence voltage control signal; and controlling the power converter according to the negative-sequence voltage control signal.

[0020] Secondly, embodiments of this application provide a power converter, the power converter comprising: a power conversion circuit; a controller, configured to adjust a positive-sequence virtual impedance within a positive-sequence limiting range based on a positive-sequence current output by the power conversion circuit, and / or adjust a negative-sequence virtual impedance within a negative-sequence limiting range based on a negative-sequence current output by the power conversion circuit; and configured to control the power conversion circuit based on the positive-sequence virtual impedance and / or the negative-sequence virtual impedance.

[0021] Optionally, the controller includes a positive sequence impedance adjustment module, which includes: a positive sequence proportional adjustment unit, used to generate a positive sequence adjustment signal based on the difference between the amplitude of the positive sequence current output by the power conversion circuit and a preset positive sequence current threshold; a positive sequence limiting unit, used to limit the positive sequence adjustment signal to generate a positive sequence limiting signal; and a positive sequence impedance calculation unit, used to generate a positive sequence virtual impedance based on the positive sequence limiting signal.

[0022] Optionally, the controller includes a negative sequence impedance adjustment module, which includes: a negative sequence proportional adjustment unit, used to generate a negative sequence adjustment signal based on the difference between the amplitude of the negative sequence current output by the power conversion circuit and a preset negative sequence current threshold; a negative sequence limiting unit, used to limit the negative sequence adjustment signal to generate a negative sequence limiting signal; and a negative sequence impedance calculation unit, used to generate a negative sequence virtual impedance based on the negative sequence limiting signal.

[0023] Thirdly, embodiments of this application provide a control device, which includes a processor and a memory. The memory is used to store computer programs, instructions, or code, and the processor is used to execute the programs, instructions, or code in the memory to implement the control method for the power converter as described in the first aspect.

[0024] In several embodiments provided in this application, the virtual impedance is adjusted and limited according to the output current of the power converter, ensuring that the virtual impedance remains within a safe range. This improves the transient stability of the power conversion system while achieving the current-limiting function of the power converter. Attached Figure Description

[0025] 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 embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0026] Figure 1 This is a control block diagram of a grid-connected inverter system in related technologies.

[0027] Figure 2 This is the equivalent circuit diagram of a grid-connected inverter system in related technologies.

[0028] Figure 3 This is a schematic flowchart of a control method for a power converter provided in one embodiment of this application.

[0029] Figure 4 A block diagram for calculating positive-sequence virtual impedance is provided for one embodiment of this application.

[0030] Figure 5 A block diagram for calculating the positive-sequence upper limit amplitude of a positive-sequence virtual impedance is provided as an embodiment of this application.

[0031] Figure 6 A block diagram for calculating negative-sequence virtual impedance is provided for one embodiment of this application.

[0032] Figure 7 A block diagram for calculating the negative-sequence upper limit magnitude of a negative-sequence virtual impedance is provided as an embodiment of this application.

[0033] Figure 8 A control block diagram of a power converter is provided for one embodiment of this application.

[0034] Figure 9 A control block diagram of a power converter is provided for another embodiment of this application.

[0035] Figure 10 This is a schematic diagram of a power converter module provided for one embodiment of this application.

[0036] Figure 11 This is a schematic diagram of a control device provided for one embodiment of this application. Detailed Implementation

[0037] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0038] In the description of the embodiments of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0039] With the continuous development of renewable energy and power electronic equipment, power converters are playing an increasingly important role in power systems. During the application of power converters, load fluctuations and other factors can cause grid voltage drops, leading to a rapid increase in the output current of the power converter and affecting its normal operation. Therefore, effective current limiting measures are needed to prevent power converters from being affected by overcurrent.

[0040] Taking grid-connected inverters as an example, traditional grid-connected inverters employ grid-following control, obtaining the voltage information of the Point of Common Coupling (PCC) through a phase-locked loop (PLL), thus synchronizing the inverter's output current with the PCC voltage. However, when grid voltage drops or other faults occur, the grid-following inverter can only synchronize the PCC voltage and cannot provide effective voltage support to the grid. To solve this problem, grid-connected inverters have gradually been applied. The control block diagram of a grid-connected inverter system is shown below. Figure 1 As shown, where V dc L represents the DC side voltage. f Indicates the filter inductance, i g V represents the grid-connected current. PCC Z represents the PCC voltage. g and v g These represent the grid impedance and grid voltage, respectively. The grid-connected inverter calculates the voltage amplitude reference E through power control. ref and phase reference θ, where P ref and Q ref These represent the active power reference and reactive power reference, respectively. Based on the voltage amplitude reference E... ref With a phase reference θ, direct control of the output voltage or output current is achieved through a voltage loop and / or a current loop.

[0041] Although grid-connected inverters can effectively support the PCC voltage, overcurrent may occur in the grid-connected current when the grid voltage drops. The equivalent circuit of a grid-connected inverter system is as follows: Figure 2 As shown, the grid-type inverter can be equivalent to a voltage source E. ref ∠θ and its output impedance Z o In a series configuration, when the grid voltage drops, the voltage difference between the equivalent voltage source of the grid-connected inverter and the grid voltage increases, leading to an increase in the output current of the grid-connected inverter. Therefore, current limiting measures need to be added to the grid-connected inverter system to protect its normal operation. However, these current limiting measures have a significant impact on the stability of the power conversion system, especially when the grid voltage experiences an asymmetrical drop, which may trigger transient instability in the power conversion system.

[0042] Therefore, how to improve the transient stability of the power conversion system while implementing the current limiting function of the power converter has become an important technical problem that needs to be solved.

[0043] Please see Figure 3 . Figure 3This application provides a control method for a power converter according to one embodiment. The control method can be applied to a control device for the power converter. The control device can be an electronic device with certain computing capabilities. Alternatively, the control device can refer to a software program running on the electronic device. In a specific embodiment, the control device can be a controller for the power converter.

[0044] The control method for this power converter includes the following steps.

[0045] Step S110: Adjust the positive sequence virtual impedance within the positive sequence limiting range according to the positive sequence current output by the power converter; and / or adjust the negative sequence virtual impedance within the negative sequence limiting range according to the negative sequence current output by the power converter.

[0046] Step S120: Control the power converter based on the positive-sequence virtual impedance and / or the negative-sequence virtual impedance.

[0047] In this embodiment, the power converter can be an inverter or other types of power conversion devices. Specifically, taking an inverter as an example, when the inverter is operating in grid-connected mode, its output current is affected by grid voltage fluctuations. Especially when the grid experiences voltage dips or asymmetrical faults, the positive-sequence and negative-sequence currents of the inverter may change significantly. The positive-sequence current typically reflects the operating state of the grid; an excessive increase in it may cause the inverter's output current to exceed the normal range, leading to overcurrent problems. The negative-sequence current is usually caused by asymmetrical faults in the grid; an excessive increase in it may affect the dynamic response and stability of the inverter system.

[0048] To protect the inverter system from overcurrent damage, especially during asymmetrical grid faults, positive-sequence and / or negative-sequence virtual impedances can be introduced. However, the introduction and adjustment of positive-sequence and / or negative-sequence virtual impedances may cause interference, affecting control performance and even leading to transient instability of the inverter system. Therefore, this embodiment adjusts the positive-sequence and / or negative-sequence virtual impedances to reduce control interference and more effectively cope with different types of grid fluctuations. Considering the dynamic and random nature of grid voltage and current fluctuations, the virtual impedance needs to be adjusted according to real-time current changes, enabling the inverter to respond quickly to changes in grid conditions. Simultaneously, to prevent excessive adjustment from causing inverter system instability, limiting control can be used to constrain the adjustment range of the virtual impedance, ensuring that the adjustment remains within a safe range and further improving the stability of the inverter system. Based on the adjusted positive-sequence virtual impedance and / or negative-sequence virtual impedance, the output voltage and current of the inverter can be adjusted, enabling the inverter to dynamically adapt to grid voltage fluctuations. This allows it to continuously provide stable voltage support to the grid during grid faults or voltage drops, thereby improving the transient stability of the inverter system.

[0049] This embodiment improves the response and stability of the power conversion system during grid faults or voltage fluctuations by adjusting the positive-sequence and / or negative-sequence virtual impedance based on the output current of the power converter, combined with a limiting control strategy. Limiting control ensures that the virtual impedance adjustment remains within a safe range, preventing instability caused by over-adjustment. Therefore, the control method in this embodiment provides stable voltage support during grid faults or voltage drops, improving the transient stability and anti-interference capability of the power conversion system while maintaining the current-limiting effect of the power converter.

[0050] In some embodiments, the control device may generate a positive sequence adjustment signal based on the difference between the amplitude of the positive sequence current output by the power converter and a preset positive sequence current threshold; perform amplitude limiting processing on the positive sequence adjustment signal to generate a positive sequence limiting signal; and generate a positive sequence virtual impedance based on the positive sequence limiting signal.

[0051] In this embodiment, the difference between the amplitude of the positive-sequence current output by the power converter and the preset positive-sequence current threshold represents the deviation between the current positive-sequence current of the power converter and the positive-sequence current threshold, reflecting the fluctuation level of the current state of the power converter. By processing this difference, a positive-sequence adjustment signal is generated, which can initially obtain the required positive-sequence impedance adjustment amplitude. In order to keep the positive-sequence adjustment signal within a reasonable range, it can be further limited to generate a positive-sequence limiting signal to prevent instability or insufficient compensation of the power conversion system due to excessive or insufficient adjustment amplitude. Based on the positive-sequence limiting signal, the positive-sequence virtual impedance can be calculated, and the positive-sequence output characteristics of the power converter can be adjusted according to the positive-sequence virtual impedance. By adjusting the positive-sequence virtual impedance, the power converter can dynamically adjust its positive-sequence output voltage and current according to changes in the power grid state, thereby effectively responding to power grid fluctuations or faults, not only improving the transient response capability of the power conversion system in the short term, but also optimizing its stability in long-term operation.

[0052] Specifically, with Figure 4 The following example illustrates the calculation method for the positive-sequence virtual impedance. In this embodiment, firstly, the control device can calculate the amplitude i of the positive-sequence current output by the power converter. gmag_p With the preset positive sequence current threshold i th The difference between them, i.e. Δi p =i gmag_p -i th Among them, i gmag_p i can be obtained in real time by a current sensor and transformed into dq coordinates. th This can be a fixed preset threshold or a dynamically adjusted reference value. The difference reflects the degree of deviation between the current positive sequence current and the expected current, which can be calculated using a subtractor. Then, the difference Δi...p Perform proportional adjustment calculations, using the proportional gain K. R_p Amplification or attenuation is performed to generate a positive sequence adjustment signal. K R_p The size of K determines the sensitivity of the adjustment; for example, a larger K... R_p This will enhance the regulation capability, enabling the positive-sequence virtual impedance to respond more quickly to changes in positive-sequence current, but may increase the instability of the power conversion system; conversely, a smaller K... R_p This makes the adjustment process smoother, which helps improve the stability of the power conversion system, but may lead to a decrease in response speed. Further, the positive-sequence adjustment signal is limited to obtain a positive-sequence limited signal, ensuring that the positive-sequence adjustment signal remains within a reasonable range and preventing instability or insufficient compensation of the power conversion system due to excessive or insufficient adjustment amplitude. Next, based on the positive-sequence limited signal, the positive-sequence virtual resistance and positive-sequence virtual reactance are calculated to determine the positive-sequence virtual impedance. Subsequently, the positive-sequence output characteristics of the power converter can be adjusted according to the calculated positive-sequence virtual impedance, including adjusting the positive-sequence output voltage and current, so that it can dynamically respond to changes in the grid state. Through the above adjustment process, the power converter can maintain stable operation under grid fluctuations or faults, thereby improving the transient response capability of the power conversion system and optimizing its long-term operational stability.

[0053] In some embodiments, the control device can compare the positive sequence adjustment signal with the positive sequence lower limit amplitude and the positive sequence upper limit amplitude, respectively, wherein the positive sequence lower limit amplitude is a preset value, and the positive sequence upper limit amplitude is generated based on the positive sequence current output by the power converter; in response to the positive sequence adjustment signal being less than the positive sequence lower limit amplitude, the positive sequence lower limit amplitude is used as the positive sequence limiting signal; or, in response to the positive sequence adjustment signal being greater than the positive sequence upper limit amplitude, the positive sequence upper limit amplitude is used as the positive sequence limiting signal; or, in response to the positive sequence adjustment signal being between the positive sequence lower limit amplitude and the positive sequence upper limit amplitude, the positive sequence adjustment signal is used as the positive sequence limiting signal.

[0054] In this embodiment, the purpose of limiting the positive sequence adjustment signal is to keep it within a reasonable range, preventing instability or insufficient compensation in the power conversion system due to excessive or insufficient adjustment. Specifically, a lower positive sequence limit and an upper positive sequence limit are first set. The lower positive sequence limit can be a preset fixed value to prevent slow response of the power conversion system due to excessively small adjustment. The upper positive sequence limit can be calculated by the power converter based on the current operating state to prevent instability caused by excessive adjustment. During the limiting process, if the positive sequence adjustment signal is less than the lower positive sequence limit, the lower positive sequence limit is used as the final positive sequence limiting signal to ensure that the adjustment is not lower than the minimum requirement. If the positive sequence adjustment signal is greater than the upper positive sequence limit, the upper positive sequence limit is used as the final positive sequence limiting signal to prevent instability of the power conversion system due to over-adjustment. If the positive sequence adjustment signal is between the lower and upper positive sequence limits, it is directly used as the positive sequence limiting signal to effectively reflect the actual requirements of the current power conversion system. By using the limiting process, the power converter's regulation signal can respond promptly to changes in the power grid state while maintaining the stability of the power conversion system, providing reliable input data for the subsequent calculation of the positive sequence virtual impedance.

[0055] Specifically, with Figure 4 For example, in this embodiment, the lower limit value of the positive sequence current is 0, that is, the amplitude i of the positive sequence current. gmag_p Less than the preset positive sequence current threshold i th When the difference between the two is less than 0, the positive sequence adjustment signal is less than the lower limit of the positive sequence amplitude. At this time, the positive sequence adjustment signal is limited to 0, i.e., the positive sequence virtual impedance is 0, to prevent unnecessary positive sequence virtual impedance adjustment under low current conditions, thereby maintaining the stability of the power conversion system. The upper limit of the positive sequence amplitude is R. vsat_p That is, when the positive sequence adjustment signal is greater than the upper limit amplitude R of the positive sequence. vsat_p At that time, the positive sequence adjustment signal is limited to R. vsat_p Within a certain range, to prevent excessively large positive-sequence virtual impedance from causing instability in the power conversion system. Specifically, during the limiting process, if the positive-sequence adjustment signal is less than 0, the positive-sequence limiting signal is 0; if the positive-sequence adjustment signal is greater than R... vsat_p Then the positive sequence limiting signal is R vsat_p If the positive sequence adjustment signal is at 0 and R vsat_p Between these points, the positive-sequence limiting signal is output according to the positive-sequence adjustment signal, reflecting the actual needs of the current power conversion system. Through this limiting process, the adjustment of the positive-sequence virtual impedance can respond promptly to changes in the power grid state while maintaining a reasonable adjustment range, thereby improving the stability and dynamic performance of the power conversion system.

[0056] In some embodiments, the upper limit amplitude of the positive sequence is obtained by multiplying the positive sequence characterization factor by a preset upper limit reference value of the positive sequence, wherein the positive sequence characterization factor is generated based on the difference between the amplitude of the positive sequence current and a preset positive sequence current threshold. The difference between the amplitude of the positive sequence current and the preset positive sequence current threshold can be processed through high-pass filtering, scaling, limiting, and offsetting to generate the positive sequence characterization factor. The lower limit amplitude of the positive sequence is 0.

[0057] In this embodiment, the positive sequence upper limit amplitude can be obtained by multiplying a positive sequence characterization factor generated from the difference between the positive sequence current amplitude and a preset positive sequence current threshold with a preset positive sequence upper limit reference value. The generation method of the positive sequence characterization factor is not limited, and includes, but is not limited to, high-pass filtering, proportional regulation, amplitude limiting, and offset processing to adapt to different operating conditions. In this way, the power converter can dynamically adjust the positive sequence upper limit amplitude according to the current operating state, making the sensitivity of the positive sequence regulation signal adapt to grid fluctuations, thereby optimizing the current limiting control effect. The positive sequence lower limit amplitude is set to 0, meaning that when the positive sequence current amplitude is less than the preset positive sequence current threshold, no positive sequence virtual impedance regulation is introduced, thereby preventing unnecessary regulation under low current conditions and helping to maintain the stability of the power conversion system. Through this adaptive amplitude limiting processing, the power conversion system can respond promptly to grid fluctuations while reducing instability caused by over-regulation, improving the responsiveness and stability of the power conversion system while ensuring the current limiting function.

[0058] Specifically, with Figure 5 The above example illustrates the calculation method for the upper limit magnitude of the positive-sequence virtual impedance. In this embodiment, the upper limit magnitude is determined by the magnitude i of the positive-sequence current. gmag_p With the preset positive sequence current threshold i th The difference between them, after high-pass filtering, scaling, limiting, and offset processing, is compared with the preset positive sequence upper limit reference value R. vref_p Multiplying them together, we get: First, the magnitude i of the positive sequence current. gmag_p With the preset positive sequence current threshold i th The difference signal between the two signals is processed by a high-pass filter HPF_p to remove low-frequency components and retain the high-frequency components of the current change. Since the high-pass filter is primarily used to remove low-frequency signals, its cutoff frequency does not need to be set too high. Then, the difference signal after high-pass filtering is adjusted by a proportional adjustment term k1, which is selected based on the specific parameters and requirements of the power conversion system. When the value of k1 is large, the positive-sequence upper limit amplitude R obtained under the same difference signal is higher. vsat_pA smaller value for k1 helps reduce the effect of the positive-sequence virtual impedance when the power conversion system is subjected to large disturbances, enhancing the adaptability of the power conversion system and reducing instability caused by over-adjustment. However, it should be noted that a larger k1 may also limit overcurrent protection; therefore, a balance needs to be struck between the participation of the positive-sequence virtual impedance and the stability of the power conversion system. Next, the proportionally adjusted signal is clipped to keep it within a reasonable range. The clipped signal is then subtracted from a constant 1, and the result is compared with the preset positive-sequence upper limit reference value R. vref_p Multiplying them together yields the upper limit magnitude R in the forward sequence. vsat_p In this way, the upper limit amplitude R of the positive sequence is... vsat_p It can adaptively adjust according to changes in positive sequence current, thereby improving the stability and responsiveness of the power conversion system while responding to grid fluctuations.

[0059] In some embodiments, the control device may use the positive sequence limiting signal as the positive sequence virtual resistor and the product of the positive sequence virtual resistor and the preset positive sequence impedance coefficient as the positive sequence virtual reactance.

[0060] In this embodiment, the positive-sequence limiting signal is used as the positive-sequence virtual resistor. Then, the positive-sequence virtual resistor is multiplied by a preset positive-sequence impedance coefficient to obtain the positive-sequence virtual reactance. The combination of the positive-sequence virtual resistor and the positive-sequence virtual reactance constitutes the positive-sequence virtual impedance. Based on this positive-sequence virtual impedance, the output voltage and current of the power converter can be adjusted, thereby regulating the response of the power conversion system and improving its stability and dynamic performance.

[0061] Specifically, still based on Figure 4 The following example illustrates the calculation method for the positive-sequence virtual impedance. In this embodiment, the positive-sequence limiting signal output after limiting processing is used as the positive-sequence virtual resistance R. v_p Positive sequence virtual resistance R v_p With the preset positive sequence impedance coefficient K X / R_p Multiplying them together yields the positive-sequence virtual reactance X. v_p Positive sequence virtual resistance R v_p and positive sequence virtual reactance X v_p The combination constitutes the positive sequence virtual impedance VI p =R v_p +jX v_p The preset positive sequence impedance coefficient K X / R The value of is not less than 3, so that the positive-sequence virtual impedance exhibits inductive characteristics. Based on this positive-sequence virtual impedance, the output voltage and current of the power converter can be effectively adjusted, improving the stability and dynamic performance of the power conversion system.

[0062] In some embodiments, the control device may generate a negative sequence adjustment signal based on the difference between the amplitude of the negative sequence current output by the power converter and a preset negative sequence current threshold; perform amplitude limiting processing on the negative sequence adjustment signal to generate a negative sequence limiting signal; and generate a negative sequence virtual impedance based on the negative sequence limiting signal.

[0063] In this embodiment, the difference between the amplitude of the negative-sequence current output by the power converter and the preset negative-sequence current threshold represents the deviation between the current negative-sequence current of the power converter and the negative-sequence current threshold, reflecting the operating state of the power converter under grid imbalance conditions and the magnitude of its negative-sequence component. By processing this difference, a negative-sequence adjustment signal is generated, which initially obtains the required negative-sequence impedance adjustment amplitude. To keep the negative-sequence adjustment signal within a reasonable range, it can be further limited to generate a negative-sequence limiting signal, preventing instability or insufficient compensation of the power conversion system due to excessive or insufficient adjustment amplitude. Based on the negative-sequence limiting signal, the negative-sequence virtual impedance can be calculated, and the negative-sequence output characteristics of the power converter can be adjusted according to this negative-sequence virtual impedance. By adjusting the negative-sequence virtual impedance, the power converter can enhance its adaptability to grid imbalance conditions, quickly adjust its negative-sequence output voltage and current, thereby effectively suppressing the fluctuation of the grid negative-sequence voltage and improving the distribution characteristics of the negative-sequence current, enhancing the fast response capability and transient stability of the power conversion system.

[0064] Specifically, with Figure 6 The following example illustrates the calculation method for the negative-sequence virtual impedance. In this embodiment, firstly, the control device can calculate the amplitude i of the negative-sequence current output by the power converter. gmag_n The difference between the current and the preset current threshold (i.e., zero). Where i gmag_n This difference can be acquired in real time by a current sensor and obtained through dq coordinate transformation. This difference reflects the magnitude of the current negative sequence current. Then, a proportional adjustment calculation is performed on this difference, using a proportional gain K. R_n Amplification or attenuation is performed to generate a negative-sequence adjustment signal. K R_n The size of K determines the sensitivity of the adjustment; for example, a larger K... R_n This will enhance the regulation capability, enabling the negative-sequence virtual impedance to respond more quickly to changes in negative-sequence current, but may increase the instability of the power conversion system; conversely, a smaller K... R_nThis makes the adjustment process smoother, which helps improve the stability of the power conversion system, but may lead to a decrease in response speed. Further, the negative-sequence adjustment signal is limited to obtain a negative-sequence limited signal, ensuring that the negative-sequence adjustment signal remains within a reasonable range and preventing instability or insufficient compensation in the power conversion system due to excessively large or small adjustment amplitudes. Next, based on the negative-sequence limited signal, the negative-sequence virtual resistance and negative-sequence virtual reactance are calculated to determine the negative-sequence virtual impedance. Subsequently, based on the calculated negative-sequence virtual impedance, the negative-sequence output characteristics of the power converter can be adjusted, including adjusting the negative-sequence output voltage and current, to enable it to respond to changes in grid imbalance, thereby effectively suppressing fluctuations in the grid's negative-sequence voltage and optimizing the distribution characteristics of the negative-sequence current.

[0065] In some embodiments, the control device can compare the negative sequence adjustment signal with the negative sequence lower limit amplitude and the negative sequence upper limit amplitude, respectively, wherein the negative sequence lower limit amplitude is a preset value, and the negative sequence upper limit amplitude is generated based on the positive sequence current and negative sequence current output by the power converter; in response to the negative sequence adjustment signal being less than the negative sequence lower limit amplitude, the negative sequence lower limit amplitude is used as the negative sequence limiting signal; or, in response to the negative sequence adjustment signal being greater than the negative sequence upper limit amplitude, the negative sequence upper limit amplitude is used as the negative sequence limiting signal; or, in response to the negative sequence adjustment signal being between the negative sequence lower limit amplitude and the negative sequence upper limit amplitude, the negative sequence adjustment signal is used as the negative sequence limiting signal.

[0066] In this embodiment, the purpose of limiting the negative sequence regulation signal is to keep it within a reasonable range, preventing instability or insufficient compensation in the power conversion system due to excessively large or small regulation amplitudes. Specifically, a lower limit and an upper limit for the negative sequence are first set. The lower limit can be a preset fixed value to prevent insufficient compensation by the power converter due to excessively small regulation amplitudes, which would prevent it from responding to grid imbalances in a timely manner. The upper limit is calculated by the power converter based on the current operating state and is used to prevent instability in the power conversion system caused by excessively large regulation amplitudes. During the limiting process, if the negative-sequence adjustment signal is less than the lower negative-sequence limit, the lower negative-sequence limit is used as the final negative-sequence limiting signal to ensure that the adjustment amplitude is not lower than the minimum requirement, thereby improving the response capability of the power conversion system. If the negative-sequence adjustment signal is greater than the upper negative-sequence limit, the upper negative-sequence limit is used as the final negative-sequence limiting signal to prevent over-adjustment from affecting the stability of the power conversion system. If the negative-sequence adjustment signal is between the lower and upper negative-sequence limits, it is directly used as the negative-sequence limiting signal, enabling it to effectively reflect the current imbalance of the power grid and the actual needs of the power converter. Through limiting, the adjustment signal of the power converter can respond promptly to changes in the power grid state while maintaining the stability of the power conversion system, providing reliable input data for the subsequent calculation of the negative-sequence virtual impedance.

[0067] Specifically, with Figure 6 For example, in this embodiment, the negative sequence lower limit value for limiting is set to 0, that is, when there is no negative sequence current in the power conversion system (i.e., i... gmag_n When the negative sequence current is 0, no negative sequence virtual impedance is introduced to prevent unnecessary negative sequence virtual impedance regulation in the absence of negative sequence current, thereby maintaining the stability of the power conversion system. The upper limit of the negative sequence current is set to R. vsat_n That is, when the negative sequence adjustment signal is greater than the upper limit amplitude R of the negative sequence. vsat_n At that time, the negative sequence adjustment signal is limited to R. vsat_n Within a certain range, to prevent excessively large negative-sequence virtual impedance from suppressing the dynamic response or causing instability in the power conversion system. Specifically, during the limiting process, if the negative-sequence adjustment signal is less than 0, the negative-sequence limiting signal is 0; if the negative-sequence adjustment signal is greater than R... vsat_n Then the negative sequence limiting signal is R vsat_n If the negative sequence limiting signal is at 0 and R vsat_n When the negative sequence is between these conditions, the negative sequence limiting signal value is output according to the negative sequence adjustment signal, reflecting the current imbalance of the power grid and the actual needs of the power converter. Through this limiting process, the adjustment of the negative sequence virtual impedance can respond promptly to changes in the power grid state while maintaining a reasonable adjustment range, thereby improving the stability and dynamic performance of the power conversion system.

[0068] In some embodiments, the negative sequence upper limit amplitude is obtained by multiplying a negative sequence characterization factor by a preset negative sequence upper limit reference value. The negative sequence characterization factor is generated based on the amplitude of the negative sequence current, the amplitude of the positive sequence current, and a preset positive sequence current threshold. The difference between the amplitude of the positive sequence current and the preset positive sequence current threshold can be high-pass filtered, squared, and summed with the square of the amplitude of the negative sequence current. This summation is then processed through scaling, limiting, and offsetting to generate the negative sequence characterization factor. The negative sequence lower limit amplitude is 0.

[0069] In this embodiment, the negative sequence upper limit amplitude can be obtained by multiplying a negative sequence characterization factor generated from the negative sequence current amplitude, the positive sequence current amplitude, and a preset positive sequence current threshold with a preset negative sequence upper limit reference value. The generation method of the negative sequence characterization factor is not limited, and includes, but is not limited to, high-pass filtering, squaring, proportional adjustment, limiting, and offsetting methods to adapt to different operating conditions. In this way, the power converter can dynamically adjust the negative sequence upper limit amplitude according to the current operating state, making the sensitivity of the negative sequence adjustment signal adaptable to grid fluctuations. Specifically, the purpose of introducing positive sequence current into the calculation of the negative sequence upper limit amplitude is to appropriately reduce the introduction of negative sequence virtual impedance when the positive sequence current is not yet stable, preventing instability of the power conversion system due to over-adjustment of the negative sequence virtual impedance. The negative sequence lower limit amplitude is set to 0, meaning that when there is no negative sequence current in the power conversion system, no negative sequence virtual impedance is introduced to avoid unnecessary negative sequence adjustment in the absence of negative sequence current, thus helping to maintain the stability of the power conversion system. Through this adaptive limiting process, the power conversion system can respond to grid fluctuations in a timely manner while reducing instability caused by over-regulation, thereby improving its response capability and stability.

[0070] Specifically, with Figure 7 The calculation method of the negative-sequence upper limit amplitude of the negative-sequence virtual impedance is shown as an example. In this embodiment, the negative-sequence upper limit amplitude is obtained by squaring the difference between the amplitude of the positive-sequence current and a preset current threshold after high-pass filtering, summing it with the square of the amplitude of the negative-sequence current, and then multiplying it by a preset negative-sequence upper limit reference value after proportional adjustment, amplitude limiting, and offset processing. Specifically, firstly, the amplitude i of the positive-sequence current... gmag_p With the preset positive sequence current threshold i th The difference signal between the two signals is processed by a high-pass filter HPF_p to remove low-frequency components and retain the high-frequency components of the current change. Since the high-pass filter is primarily used to remove low-frequency signals, its cutoff frequency does not need to be set too high. Then, the high-pass filtered difference signal is squared and compared with the amplitude i of the negative sequence current. gmag_nThe squares of the values ​​are summed. The summed signal is then adjusted using a proportional adjustment term k2, which is selected based on the specific parameters and requirements of the power conversion system. A larger value of k2 enhances the adaptability of the power conversion system and reduces the effect of the negative-sequence virtual impedance, especially when the power conversion system is subjected to large disturbances. This helps prevent instability caused by over-adjustment. However, it should be noted that a larger k2 may also limit overcurrent protection; therefore, a balance needs to be struck between the participation of the negative-sequence virtual impedance and the stability of the power conversion system. Next, the proportionally adjusted signal is amplitude-limited to keep it within a reasonable range. The difference between the amplitude-limited signal and a constant 1 is then calculated, and the result is compared with the preset negative-sequence upper limit reference value R. vref_n Multiplying them together yields the negative-order upper limit magnitude R. vsat_n In this embodiment, the purpose of introducing positive-sequence current into the negative-sequence upper limit amplitude is to appropriately reduce the introduction of negative-sequence virtual impedance before the positive-sequence current stabilizes, thus preventing instability of the power conversion system due to excessive adjustment of the negative-sequence virtual impedance. In this way, the negative-sequence upper limit amplitude R... vsat_n It can adaptively adjust according to changes in both negative and positive sequence currents, thereby improving the response capability and stability of the power conversion system while responding to grid fluctuations.

[0071] In some embodiments, the control device may use the negative sequence limiting signal as the negative sequence virtual resistor and the product of the negative sequence virtual resistor and the preset negative sequence impedance coefficient as the negative sequence virtual reactance.

[0072] In this embodiment, the negative-sequence limiting signal is used as a negative-sequence virtual resistor. Then, this negative-sequence virtual resistor is multiplied by a preset negative-sequence impedance coefficient to obtain the negative-sequence virtual reactance. The combination of the negative-sequence virtual resistor and the negative-sequence virtual reactance constitutes the negative-sequence virtual impedance. Based on this negative-sequence virtual impedance, the output voltage and current of the inverter can be adjusted, thereby achieving regulation of the power conversion system response and improving its stability and dynamic performance.

[0073] Specifically, still based on Figure 6 The following example illustrates the calculation method for the negative-sequence virtual impedance. In this embodiment, the negative-sequence limiting signal output after limiting processing is used as the negative-sequence virtual resistance R. v_n Negative sequence virtual resistance R v_n With the preset negative sequence impedance coefficient K X / R_n Multiplying them together yields the negative-sequence virtual reactance X. v_n The combination of negative-sequence virtual resistance and negative-sequence virtual reactance constitutes the negative-sequence virtual impedance VI. n =R v_n +jX v_n The preset negative sequence impedance coefficient K X / RThe value of is not less than 3, so that the negative-sequence virtual impedance exhibits inductive characteristics. Based on this negative-sequence virtual impedance, the output voltage and current of the power converter can be effectively adjusted, improving the stability and dynamic performance of the power conversion system.

[0074] In some embodiments, the control device may also take the difference between the preset positive sequence reference voltage and the positive sequence voltage output by the power converter and the voltage obtained by multiplying the positive sequence current and the positive sequence virtual impedance to generate a positive sequence voltage error signal; perform voltage loop regulation on the positive sequence voltage error signal to generate a positive sequence voltage control signal; and control the power converter according to the positive sequence voltage control signal.

[0075] Specifically, with Figure 8 The control of a power converter is illustrated as an example. In this embodiment, the control device performs calculations and control in a synchronous rotating coordinate system (dq coordinate system). First, the control device calculates the dq component E of the preset positive sequence reference voltage using a subtractor. refdq_p The dq component V of the positive sequence voltage output by the power converter PCCdq_p and positive sequence virtual impedance VI p The difference between the generated voltages produces a positive-sequence voltage error signal. The positive-sequence virtual impedance VI is used to generate this signal. p The generated voltage is composed of the dq component of the positive sequence current, i gdq_p With positive sequence virtual impedance VI p Multiplying them together gives the positive-sequence reference voltage E. refdq_p The system can be dynamically adjusted based on the operating status or control objectives of the power conversion system. Then, the control device inputs the positive sequence voltage error signal to the positive sequence voltage loop regulator Gv_p for adjustment, generating the positive sequence voltage control signal V. Mdq_p The positive sequence voltage loop regulator Gv_p can be a PI regulator. Next, the control device controls the voltage according to the positive sequence voltage control signal V. Mdq_p The positive-sequence voltage output by the power converter is adjusted to gradually approach a preset positive-sequence reference voltage, thereby improving the stability of the power converter. Of course, in some other embodiments, a positive-sequence current loop regulator can also be added to regulate the positive-sequence current output by the power converter; this application does not limit this.

[0076] In some embodiments, the control device may further subtract a preset negative-sequence reference voltage from the negative-sequence voltage output by the power converter and the voltage obtained by multiplying the negative-sequence current and the negative-sequence virtual impedance to generate a negative-sequence voltage error signal; perform voltage loop regulation on the negative-sequence voltage error signal to generate a negative-sequence voltage control signal; and control the power converter according to the negative-sequence voltage control signal.

[0077] Specifically, with Figure 9The control of a power converter is illustrated as an example. In this embodiment, the control device performs calculations and control in a synchronous rotating coordinate system (dq coordinate system). First, the control device calculates the dq component (usually zero) of a preset negative-sequence reference voltage and the dq component V of the negative-sequence voltage output by the power converter using a subtractor. PCCdq_n and negative sequence virtual impedance VI n The difference between the generated voltages produces a negative-sequence voltage error signal. The negative-sequence virtual impedance VI... n The generated voltage is composed of the dq component of the negative sequence current i gdq_n With negative sequence virtual impedance VI n The result is obtained by multiplication. Then, the control device inputs the negative sequence voltage error signal to the negative sequence voltage loop regulator Gv_n for adjustment, generating the negative sequence voltage control signal V. Mdq_n The negative sequence voltage loop regulator Gv_p can be a PI regulator. Next, the control device controls the signal V based on the negative sequence voltage. Mdq_n The negative sequence voltage output by the power converter is adjusted to gradually approach a preset negative sequence reference voltage, thereby improving the stability of the power converter. Of course, in some other embodiments, a negative sequence current loop regulator can also be added to regulate the negative sequence current output by the power converter; this application does not limit this.

[0078] Please see Figure 10 This application also provides a power converter. The power converter includes a power conversion circuit 110 and a controller 120, wherein the controller 120 is used to adjust the positive-sequence virtual impedance within a positive-sequence limiting range according to the positive-sequence current output by the power conversion circuit 110, and / or adjust the negative-sequence virtual impedance within a negative-sequence limiting range according to the negative-sequence current output by the power conversion circuit 110; and is used to control the power conversion circuit 110 according to the positive-sequence virtual impedance and / or the negative-sequence virtual impedance.

[0079] In this embodiment, the controller 120 of the power converter can adjust the corresponding virtual impedance within the positive or negative sequence limiting range according to the positive sequence current and / or negative sequence current output by the power conversion circuit 110, and control the power conversion circuit 110 based on the adjusted virtual impedance. With this configuration, the power converter can provide stable voltage support during grid faults or voltage drops, ensuring the current limiting effect of the power converter while enhancing the transient stability and anti-interference capability of the power conversion system.

[0080] In some embodiments, the controller includes a positive sequence impedance adjustment module, which includes: a positive sequence proportional adjustment unit for generating a positive sequence adjustment signal based on the difference between the amplitude of the positive sequence current output by the power conversion circuit and a preset positive sequence current threshold; a positive sequence limiting unit for limiting the positive sequence adjustment signal to generate a positive sequence limiting signal; and a positive sequence impedance calculation unit for generating a positive sequence virtual impedance based on the positive sequence limiting signal.

[0081] In some embodiments, the controller includes a negative sequence impedance adjustment module, which includes: a negative sequence proportional adjustment unit for generating a negative sequence adjustment signal based on the difference between the amplitude of the negative sequence current output by the power conversion circuit and a preset negative sequence current threshold; a negative sequence limiting unit for limiting the negative sequence adjustment signal to generate a negative sequence limiting signal; and a negative sequence impedance calculation unit for generating a negative sequence virtual impedance based on the negative sequence limiting signal.

[0082] For the other specific functions and effects of each module in the power converter, please refer to the foregoing embodiments for explanation, and they will not be repeated here.

[0083] This application also provides a control device, including a processor and a memory. The memory is used to store computer programs, instructions, or code, and the processor is used to execute the programs, instructions, or code in the memory to perform the control method as described in the foregoing embodiments.

[0084] In this embodiment, please refer to Figure 11 The control device may include a memory 101 and a processor 102. The processor 102 may be connected to the power conversion circuit 103 and may issue control commands to the power conversion circuit 103. The memory 101 may be random access memory (RAM), flash memory, read-only memory (ROM), EPROM, non-volatile read-only memory (EEPROM), registers, hard disk, removable disk, etc.

[0085] The memory 101 can store computer instructions. When the computer instructions stored in the memory 101 are executed by the processor 102, the processor 102 can be used to execute the aforementioned control method.

[0086] 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. A 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 flow or function according to the embodiments of this application is 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 a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, 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 that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape) or a semiconductor medium (e.g., solid-state disk (SSD)).

[0087] This application also provides a readable storage medium for storing the control methods or algorithms provided in the above embodiments. Examples include random access memory (RAM), flash memory, read-only memory (ROM), EPROM, non-volatile read-only memory (EPROM), registers, hard disks, removable disks, or any other form of storage medium in the art.

[0088] It is understood that the term "connection" in the embodiments of this application can be interpreted as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc. can transmit electrical signals or data to each other.

[0089] It is understood that the specific examples in this document are only intended to help those skilled in the art better understand the embodiments of this application, and are not intended to limit the scope of the invention.

[0090] It is understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0091] It is understood that the various embodiments described in this application can be implemented individually or in combination, and the embodiments of this application are not limited in this respect.

[0092] Unless otherwise stated, all technical and scientific terms used in the embodiments of this application have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The term "and / or" as used in this application includes any and all combinations of one or more of the associated listed items. The singular forms "a," "the," and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0093] Those skilled in the art will 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, 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.

[0094] The above description is merely a specific embodiment of this application, but the scope of protection of this invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this invention should be determined by the scope of the claims.

Claims

1. A control method for a power converter, characterized in that, The control method includes: Based on the positive sequence current output by the power converter, the positive sequence virtual impedance is adjusted within the positive sequence limiting range; and / or, based on the negative sequence current output by the power converter, the negative sequence virtual impedance is adjusted within the negative sequence limiting range. The power converter is controlled based on the positive-sequence virtual impedance and / or the negative-sequence virtual impedance.

2. The control method according to claim 1, characterized in that, The step of adjusting the positive-sequence virtual impedance within the positive-sequence limiting range based on the positive-sequence current output by the power converter includes: A positive sequence adjustment signal is generated based on the difference between the amplitude of the positive sequence current output by the power converter and the preset positive sequence current threshold. The positive sequence adjustment signal is subjected to amplitude limiting processing to generate a positive sequence amplitude limiting signal; Based on the positive-sequence limiting signal, a positive-sequence virtual impedance is generated.

3. The control method according to claim 2, characterized in that, The step of limiting the positive-sequence adjustment signal to generate a positive-sequence limited signal includes: The positive sequence adjustment signal is compared with the positive sequence lower limit amplitude and the positive sequence upper limit amplitude, respectively, wherein the positive sequence lower limit amplitude is a preset value, and the positive sequence upper limit amplitude is generated according to the positive sequence current output by the power converter; In response to the positive sequence adjustment signal being less than the positive sequence lower limit amplitude value, the positive sequence lower limit amplitude value is used as the positive sequence limiting signal; or... In response to the positive sequence adjustment signal being greater than the positive sequence upper limit amplitude, the positive sequence upper limit amplitude is used as the positive sequence limiting signal; or... In response to the positive sequence adjustment signal being between the positive sequence lower limit amplitude value and the positive sequence upper limit amplitude value, the positive sequence adjustment signal is used as a positive sequence limiting signal.

4. The control method according to claim 3, characterized in that, The positive sequence upper limit amplitude is obtained by multiplying the positive sequence characterization factor by a preset positive sequence upper limit benchmark value, wherein the positive sequence characterization factor is generated based on the difference between the positive sequence current amplitude and the preset positive sequence current threshold.

5. The control method according to claim 4, characterized in that, The positive sequence characterization factor is generated based on the difference between the magnitude of the positive sequence current and a preset positive sequence current threshold, including: The difference between the amplitude of the positive sequence current and the preset positive sequence current threshold is used to generate the positive sequence characterization factor through high-pass filtering, scaling, limiting and offset processing.

6. The control method according to claim 4, characterized in that, The lower limit value for the positive sequence is 0.

7. The control method according to any one of claims 2 to 6, characterized in that, The step of generating a positive-sequence virtual impedance based on the positive-sequence limiting signal includes: The positive-sequence limiting signal is used as the positive-sequence virtual resistor, and the product of the positive-sequence virtual resistor and the preset positive-sequence impedance coefficient is used as the positive-sequence virtual reactance.

8. The control method according to claim 1, characterized in that, The step of adjusting the negative-sequence virtual impedance within the negative-sequence limiting range based on the negative-sequence current output by the power converter includes: A negative sequence adjustment signal is generated based on the difference between the amplitude of the negative sequence current output by the power converter and the preset negative sequence current threshold. The negative sequence adjustment signal is subjected to amplitude limiting processing to generate a negative sequence amplitude limiting signal; Based on the negative sequence limiting signal, a negative sequence virtual impedance is generated.

9. The control method according to claim 8, characterized in that, The step of limiting the negative-sequence adjustment signal to generate a negative-sequence limited signal includes: The negative sequence adjustment signal is compared with the negative sequence lower limit amplitude and the negative sequence upper limit amplitude, respectively, wherein the negative sequence lower limit amplitude is a preset value, and the negative sequence upper limit amplitude is generated based on the positive sequence current and negative sequence current output by the power converter; In response to the negative sequence adjustment signal being less than the negative sequence lower limit amplitude value, the negative sequence lower limit amplitude value is used as the negative sequence limiting signal; or... In response to the negative sequence adjustment signal being greater than the negative sequence upper limit amplitude, the negative sequence upper limit amplitude is used as the negative sequence limiting signal; or... In response to the negative sequence adjustment signal being between the negative sequence lower limit amplitude value and the negative sequence upper limit amplitude value, the negative sequence adjustment signal is used as a negative sequence limiting signal.

10. The control method according to claim 9, characterized in that, The negative sequence upper limit amplitude is obtained by multiplying the negative sequence characterization factor by a preset negative sequence upper limit benchmark value, wherein the negative sequence characterization factor is generated based on the amplitude of the negative sequence current, the amplitude of the positive sequence current, and a preset positive sequence current threshold.

11. The control method according to claim 10, characterized in that, The negative sequence characterization factor is generated based on the amplitude of the negative sequence current, the amplitude of the positive sequence current, and a preset positive sequence current threshold, and includes: The difference between the amplitude of the positive-sequence current and the preset positive-sequence current threshold is squared after high-pass filtering, and then summed with the square of the amplitude of the negative-sequence current. After scaling, limiting and offsetting, the negative-sequence characterization factor is generated.

12. The control method according to claim 9, characterized in that, The negative order lower limit amplitude is 0.

13. The control method according to any one of claims 8 to 12, characterized in that, The step of generating a negative-sequence virtual impedance based on the negative-sequence limiting signal includes: The negative sequence limiting signal is used as the negative sequence virtual resistor, and the product of the negative sequence virtual resistor and the preset negative sequence impedance coefficient is used as the negative sequence virtual reactance.

14. The control method according to claim 1, characterized in that, The control method further includes: The positive sequence reference voltage is subtracted from the positive sequence voltage output by the power converter and the voltage obtained by multiplying the positive sequence current and the positive sequence virtual impedance to generate a positive sequence voltage error signal. The positive sequence voltage error signal is subjected to voltage loop regulation to generate a positive sequence voltage control signal; The power converter is controlled according to the positive sequence voltage control signal.

15. The control method according to claim 1, characterized in that, The control method further includes: The negative sequence voltage error signal is generated by subtracting the preset negative sequence reference voltage from the negative sequence voltage output by the power converter and the voltage obtained by multiplying the negative sequence current and the negative sequence virtual impedance. The negative sequence voltage error signal is subjected to voltage loop regulation to generate a negative sequence voltage control signal; The power converter is controlled according to the negative sequence voltage control signal.

16. A power converter, characterized in that, The power converter includes: Power conversion circuit; The controller is configured to adjust the positive-sequence virtual impedance within a positive-sequence limiting range based on the positive-sequence current output by the power conversion circuit, and / or adjust the negative-sequence virtual impedance within a negative-sequence limiting range based on the negative-sequence current output by the power conversion circuit; and to control the power conversion circuit based on the positive-sequence virtual impedance and / or the negative-sequence virtual impedance.

17. The power converter according to claim 16, characterized in that, The controller includes a positive-sequence impedance adjustment module, which includes: The positive sequence proportional adjustment unit is used to generate a positive sequence adjustment signal based on the difference between the amplitude of the positive sequence current output by the power conversion circuit and a preset positive sequence current threshold. The positive sequence limiting unit is used to perform limiting processing on the positive sequence adjustment signal to generate a positive sequence limiting signal; The positive sequence impedance calculation unit is used to generate a positive sequence virtual impedance based on the positive sequence limiting signal.

18. The power converter according to claim 16, characterized in that, The controller includes a negative sequence impedance adjustment module, which includes: The negative sequence proportional adjustment unit is used to generate a negative sequence adjustment signal based on the difference between the amplitude of the negative sequence current output by the power conversion circuit and a preset negative sequence current threshold. The negative sequence limiting unit is used to perform limiting processing on the negative sequence adjustment signal to generate a negative sequence limiting signal. The negative sequence impedance calculation unit is used to generate a negative sequence virtual impedance based on the negative sequence limiting signal.

19. A control device, characterized in that, The control device includes a processor and a memory, the memory being used to store computer programs, instructions, or code, and the processor being used to execute the programs, instructions, or code in the memory to implement the control method of the power converter as described in any one of claims 1 to 15.

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