A method, system, and device for low-frequency stability control of grid-type converters based on passive enhancement.

Abstract

This invention relates to a low-frequency stability control method, system, and apparatus for grid-type converters based on passive performance enhancement. The method includes a synchronization stage, a reactive power control stage, a virtual impedance stage, and an inner-loop control stage. It further includes: extracting a frequency disturbance signal from the synchronization stage, filtering it through a high-pass filter, and then integrating it to obtain the controller phase disturbance, which is multiplied by an electromotive force (EMF) reference amplitude to obtain a q-axis voltage compensation component, which is then applied to the input of the q-axis voltage control in the inner-loop control stage; extracting a reactive power error signal from the reactive power control stage, multiplying it by a reactive power droop control coefficient, and then processing it through a high-pass filter to obtain a d-axis EMF reference signal disturbance, which is then applied to the input of the d-axis voltage control in the inner-loop control stage. Compared with existing technologies, this invention can effectively eliminate the negative impact of phase disturbance and EMF reference signal disturbance on passive performance, ensuring the low-frequency stability of the grid-type converter.

Description

Technical Field

[0001] This invention relates to the field of grid-type converter control technology, and in particular to a method, system and device for low-frequency stability control of grid-type converters based on passive performance enhancement. Background Technology

[0002] The power system is currently undergoing a profound energy transition, with the penetration rate of new energy sources, represented by wind power and photovoltaics, continuously increasing. Compared to traditional grid-connected converters, grid-connected converters, due to their ability to autonomously construct voltage and frequency, can provide the necessary voltage and frequency support for new power systems with low inertia and weak damping, thus becoming key grid-connected equipment. However, grid-connected converters contain multiple components, including synchronous control, reactive power control, virtual impedance, inner-loop control, and LC filtering, resulting in extremely complex dynamic characteristics. The system impedance model exhibits typical high-order coupling characteristics of multiple inputs and multiple outputs.

[0003] In existing research and engineering practice, the analysis of grid-connected stability of grid-connected converters mainly relies on full-order small-signal models or impedance models. Due to the numerous control components and the complex coupling terms in the impedance matrix, researchers find it difficult to intuitively elucidate the low-frequency oscillation risk mechanism when grid-connected converters are connected to the grid, and it is also difficult to directly guide the design of stability control strategies from a mechanistic perspective. In-depth analysis based on passive theory shows that, as a multi-input multi-output system, the passive nature of a grid-connected converter must be determined through the impedance matrix. Although its diagonal impedance terms typically exhibit positive damping characteristics, due to the dynamics of the power outer loop control and the influence of virtual inductance, its off-diagonal elements (i.e., the coupling impedance between the d and q axes) have large amplitudes in the low-frequency range. This directly leads to key indicators in the passive nature criterion (such as the real part of the matrix eigenvalues) being negative over a wide frequency range. This passive damage caused by high-order coupling produces a negative damping effect, which is the fundamental cause of low-frequency oscillations in grid-connected systems under weak grid conditions.

[0004] To suppress oscillations and improve stability, existing technologies mainly employ parameter optimization or additional control strategies, but both have certain limitations. Simply optimizing control parameters (such as adjusting the virtual inertia coefficient or damping coefficient) can improve the system's stability margin to some extent, but this usually comes at the cost of sacrificing the system's dynamic response speed. Furthermore, changes in grid operation modes cause time-varying grid strength (short-circuit ratio), making it difficult for fixed control parameters to consistently guarantee system stability under varying grid conditions. Regarding additional control strategies, some literature proposes an active power reference signal feedforward control strategy, which can improve the system's dynamic performance through near-zero pole cancellation, but it cannot change the distribution of closed-loop poles, thus failing to fundamentally improve the system's stability margin. Another type of control strategy based on active and reactive power cross-decoupling, while achieving control decoupling to some extent, still has a limited stable operating range under extremely weak grid conditions or large disturbances, and its complex control structure increases the difficulty of engineering implementation. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art by providing a low-frequency stability control method, system, and device for grid-type converters based on passive performance enhancement, effectively eliminating the negative impact of phase disturbances and electromotive force reference signal disturbances on passive performance.

[0006] The objective of this invention can be achieved through the following technical solutions: A low-frequency stability control method for a grid-type converter based on passive performance enhancement, wherein the grid-type converter includes interconnected DC current and AC circuits, and the control method for the grid-type converter includes a synchronization element, a reactive power control element, a virtual impedance element, and an inner loop control element. The control method further includes: extracting a frequency disturbance signal from the synchronization link, filtering the frequency disturbance signal through a high-pass filter and integrating it to obtain the controller phase disturbance, multiplying it by the electromotive force reference amplitude to obtain the q-axis voltage compensation component, and compensating it to the input terminal of the q-axis voltage control of the inner loop control link; The reactive power error signal is extracted from the reactive power control loop, multiplied by the reactive power droop control coefficient, and then processed by a high-pass filter to obtain the d-axis electromotive force reference signal disturbance, which is then compensated to the input terminal of the d-axis voltage control of the inner loop control loop.

[0007] Furthermore, the process of obtaining the d-axis electromotive force reference signal disturbance specifically includes: Obtain the reactive power output of the converter Q o High-frequency noise is filtered out by a low-pass filter to obtain the reactive power after filtering. reactive power reference value Qref Subtract the filtered reactive power, then multiply by the reactive power droop control factor. n q Then, the signal is processed by a high-pass filter to obtain the d-axis electromotive force reference signal perturbation.

[0008] Furthermore, the d-axis electromotive force reference signal disturbance compensation to the input terminal of the d-axis voltage control of the inner loop control loop specifically involves: The PCC voltage reference signal controlled by the d-axis voltage of the inner loop control loop. v dref The disturbance of the d-axis electromotive force reference signal is subtracted for control.

[0009] Furthermore, the process of obtaining the q-axis voltage compensation component specifically includes: Obtain the active power output of the converter P o The active power reference value P ref Subtract the active power output of the converter P o The difference in active power is obtained. Subtract the feedback amount from the active power difference, and then divide by the virtual moment of inertia. J The frequency offset is then obtained by integration. The feedback quantity is the frequency offset multiplied by the virtual damping coefficient. D p The result; The frequency offset is filtered by a high-pass filter and then integrated to obtain the controller phase disturbance. This controller phase disturbance is then multiplied by the electromotive force reference amplitude. E ref The q-axis voltage compensation component is obtained.

[0010] Furthermore, the q-axis voltage compensation component is specifically compensated to the input terminal of the q-axis voltage control of the inner loop control loop as follows: The PCC voltage reference signal controlled by the q-axis voltage of the inner loop control loop. v qref The q-axis voltage compensation component is subtracted for control purposes.

[0011] Furthermore, the output of the virtual impedance link is connected to the inner loop control link, and the outputs of both the reactive power control link and the inner loop control link are connected to the synchronization link. The outputs of the synchronization link and the inner loop control link control the AC circuit.

[0012] Furthermore, the synchronization link adopts a method based on the active power output of the converter. P oThe active power control or DC control based on a constant voltage source generates a phase signal for coordinate transformation of system voltage and current, thereby generating a control signal for the three-phase full-bridge inverter circuit of the AC circuit through PWM.

[0013] Furthermore, the reactive power control circuit is based on the reactive power output of the converter. Q o Generate d-axis electromotive force reference signal e dref q-axis electromotive force reference signal e qref The value is given as 0.

[0014] Furthermore, the virtual impedance element is used to convert the three-phase grid-connected current... i oabc dq components obtained after coordinate transformation i od and i oq All are through the corresponding virtual resistors R v and inductance value L v The dq component of the PCC voltage reference signal is generated after performing virtual impedance calculation. v dref and v qref .

[0015] Furthermore, the inner loop control circuit includes a voltage source and a current loop connected in sequence. The voltage source uses PI control to make the PCC voltage follow the reference value and outputs the dq component of the inductor current reference signal. i dref and i qref ; The current loop is based on the dq component of the inductor current reference signal. i dref and i qref By employing proportional control and combining it with the phase signal of the synchronization element for coordinate transformation, a three-phase modulated wave signal is ultimately output. v mabc .

[0016] This invention also provides a low-frequency stability control system for a grid-type converter based on passive performance enhancement. The grid-type converter includes interconnected DC and AC circuits. The control system includes a synchronization element, a reactive power control element, a virtual impedance element, and an inner-loop control element. The control system further includes: The first additional branch is used to extract the frequency disturbance signal from the synchronization link, filter the frequency disturbance signal through a high-pass filter and integrate it to obtain the controller phase disturbance, and multiply it by the electromotive force reference amplitude to obtain the q-axis voltage compensation component, which is then compensated to the input terminal of the q-axis voltage control of the inner loop control link. The second additional branch is used to extract the reactive power error signal from the reactive power control loop, multiply it by the reactive power droop control coefficient, process it through a high-pass filter to obtain the d-axis electromotive force reference signal disturbance, and compensate it to the input terminal of the d-axis voltage control of the inner loop control loop.

[0017] Furthermore, the second additional branch includes: The d-axis electromotive force reference signal disturbance acquisition unit is used to extract the reactive power error signal from the reactive power control loop, multiply it by the reactive power droop control coefficient, and then process it through a high-pass filter to obtain the d-axis electromotive force reference signal disturbance. The d-axis voltage control compensation unit is used to compensate for the disturbance of the d-axis electromotive force reference signal to the input terminal of the d-axis voltage control of the inner loop control loop.

[0018] Furthermore, the d-axis electromotive force reference signal disturbance acquisition unit specifically includes: Obtain the reactive power output of the converter Q o High-frequency noise is filtered out by a low-pass filter to obtain the reactive power after filtering. reactive power reference value Q ref Subtract the filtered reactive power, then multiply by the reactive power droop control factor. n q Then, the perturbation of the d-axis electromotive force reference signal is obtained by processing through a high-pass filter; The d-axis voltage control compensation unit is specifically as follows: The PCC voltage reference signal controlled by the d-axis voltage of the inner loop control loop. v dref The disturbance of the d-axis electromotive force reference signal is subtracted for control.

[0019] Furthermore, the second additional branch includes: The q-axis voltage compensation component acquisition unit is used to extract the frequency disturbance signal from the synchronization link, filter the frequency disturbance signal through a high-pass filter and integrate it to obtain the controller phase disturbance, and multiply it by the electromotive force reference amplitude to obtain the q-axis voltage compensation component. The q-axis voltage control compensation unit is used to compensate the q-axis voltage compensation component to the input terminal of the q-axis voltage control of the inner loop control loop.

[0020] Furthermore, the q-axis voltage compensation component acquisition unit specifically includes: Obtain the active power output of the converter P o The active power reference value P ref Subtract the active power output of the converter P o The difference in active power is obtained. Subtract the feedback amount from the active power difference, and then divide by the virtual moment of inertia. J The frequency offset is then obtained by integration. The feedback quantity is the frequency offset multiplied by the virtual damping coefficient. D p The result; The frequency offset is filtered by a high-pass filter and then integrated to obtain the controller phase disturbance. This controller phase disturbance is then multiplied by the electromotive force reference amplitude. E ref The q-axis voltage compensation component is obtained; The q-axis voltage control compensation unit is specifically as follows: The PCC voltage reference signal controlled by the q-axis voltage of the inner loop control loop. v qref The q-axis voltage compensation component is subtracted for control purposes.

[0021] Furthermore, the output of the virtual impedance link is connected to the inner loop control link, and the outputs of both the reactive power control link and the inner loop control link are connected to the synchronization link. The outputs of the synchronization link and the inner loop control link control the AC circuit. The synchronization mechanism adopts a method based on the active power output of the converter. P o The active power control or DC control based on a constant voltage source generates a phase signal for coordinate transformation of system voltage and current, thereby generating a control signal for the three-phase full-bridge inverter circuit of the AC circuit through PWM.

[0022] Furthermore, the reactive power control circuit is based on the reactive power output of the converter. Q o Generate d-axis electromotive force reference signal e dref q-axis electromotive force reference signal e qref The value is given as 0.

[0023] Furthermore, the virtual impedance element is used to convert the three-phase grid-connected current... i oabc dq components obtained after coordinate transformation iod and i oq All are through the corresponding virtual resistors R v and inductance value L v The dq component of the PCC voltage reference signal is generated after performing virtual impedance calculation. v dref and v qref .

[0024] Furthermore, the inner loop control circuit includes a voltage source and a current loop connected in sequence. The voltage source uses PI control to make the PCC voltage follow the reference value and outputs the dq component of the inductor current reference signal. i dref and i qref ; The current loop is based on the dq component of the inductor current reference signal. i dref and i qref By employing proportional control and combining it with the phase signal of the synchronization element for coordinate transformation, a three-phase modulated wave signal is ultimately output. v mabc .

[0025] The present invention also provides a low-frequency stability control device for a grid-type converter based on passive performance enhancement, comprising a memory and a processor, wherein the memory stores a computer program, and the processor calls the computer program to execute the steps of the method described above.

[0026] Compared with the prior art, the present invention has the following advantages: (1) This invention is based on the low-frequency reduced-order model to locate the instability mechanism. By introducing two specific compensation branches in the inner loop control loop, the first additional branch extracts the frequency disturbance signal from the synchronization link. The signal passes through a high-pass filter and an integrator to obtain the controller phase disturbance. The phase disturbance is multiplied by the electromotive force reference amplitude to obtain the q-axis voltage compensation component. The compensation component is superimposed on the input of the q-axis voltage control to weaken the output impedance of the converter. Z qd The impact on passivity; The second additional branch extracts the d-axis electromotive force reference signal disturbance from the reactive power control stage through a high-pass filter and compensates it at the input of the d-axis voltage control to reduce the output impedance of the converter. Z dq The impact on passivity; This invention effectively eliminates the negative impact of phase disturbances and electromotive force reference signal disturbances on passivity by introducing a specific compensation branch to reshape the coupling term of the converter output impedance. Without sacrificing the dynamic performance of the system, it effectively improves the passivity and stability margin of the system and ensures the low-frequency stability of the grid-type converter.

[0027] (2) The present invention effectively adapts to extremely weak power grid conditions, expands the stable operating boundary, and does not sacrifice the original steady-state and dynamic response performance of the system.

[0028] (3) The present invention only requires an additional compensation branch to be connected in parallel in the original voltage control loop, without changing other control structures of the converter, which is simple to implement and has low cost. Attached Figure Description

[0029] Figure 1 The grid converter topology and control block diagram are provided in this embodiment of the invention for the application of a low-frequency stability control method for a grid converter based on passive performance enhancement. Figure 2 This is a block diagram of a stability control strategy for a low-frequency stability control method for a grid-type converter based on passive performance enhancement, provided in an embodiment of the present invention. Figure 3 This is a low-frequency transfer block diagram of a GFM converter with added stability enhancement control provided in an embodiment of the present invention; Figure 4 This invention provides an example of improving the output impedance of a converter after adding a compensation branch. Figure 5 This is an example of an improvement in the passivity of a converter after adding a compensation branch, as provided in an embodiment of the present invention. Figure 6 This is a solution result of the stability domain of a converter grid-connected system with and without a compensation branch, provided in an embodiment of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0031] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0032] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0033] In the description of this invention, it should be noted 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, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0034] Example 1 like Figure 1 As shown, this embodiment provides a low-frequency stability control method for a grid-type converter based on passive performance enhancement. The grid-type converter includes interconnected DC and AC circuits. The control method for the grid-type converter includes a synchronization link, a reactive power control link, a virtual impedance link, and an inner loop control link. The output of the virtual impedance link is connected to the inner loop control link. The outputs of the reactive power control link and the inner loop control link are both connected to the synchronization link. The outputs of the synchronization link and the inner loop control link control the AC circuit. Specifically, the synchronization stage (green part) adopts a method based on the active power output of the converter. P o The active power control or DC control based on a constant voltage source generates a phase signal for coordinate transformation of system voltage and current, thereby generating a control signal for the three-phase full-bridge inverter circuit of the AC circuit through PWM.

[0035] The reactive power control circuit (red section) is based on the reactive power output of the converter. Q o Generate d-axis electromotive force reference signal e dref q-axis electromotive force reference signal e qref If the value is directly set to 0, a low-pass filter (LPF) can be added to filter out [the pollutants]. Q o High-frequency noise in the medium.

[0036] The virtual impedance element (gray area) is used to reshape the output characteristics of the converter, converting the three-phase grid-connected current... i oabc dq components obtained after coordinate transformation i od and i oq All are through the corresponding virtual resistors Rv and inductance value L v The dq component of the PCC voltage reference signal is generated after performing virtual impedance calculation. v dref and v qref .

[0037] The inner loop control (blue part) adopts a dual closed-loop control structure of PCC voltage and inductor current, including a voltage source and a current loop connected in sequence. The voltage source uses PI control to make the PCC voltage follow the reference value, and outputs the dq component of the inductor current reference signal. i dref and i qref ; The current loop is based on the dq component of the inductor current reference signal. i dref and i qref Proportional control is employed, and coordinate transformation is performed using the phase signal from the synchronization element to ultimately output a three-phase modulated wave signal. v mabc .

[0038] This can increase the inner loop response speed and provide active damping. To improve control dynamics, capacitor voltage decoupling control can be added to the voltage loop, and inductor current decoupling control and PCC voltage feedforward control can be added to the current loop.

[0039] When a grid-connected (GFM) converter is running, external conditions such as grid strength will change with dispatch commands. This requires the controller to have sufficient robustness to resist the risk of instability caused by changes in external conditions. In the field of robust control, passive theory is a classic analysis method. For a single-input single-output (SISO) system, the passive requirements are: (1) the converter impedance transfer function itself does not contain right half-plane poles; (2) the phase of the impedance transfer function is maintained within the (90°, 90°) interval. For a multiple-input multiple-output (MIMO) system such as a converter, its passiveness must be determined by the impedance matrix. Let its output impedance expression be: (1) According to equation (1), the active power input to the converter at the grid connection port is defined as: (2) In the formula, the superscript "H" denotes the Hermite operator. Passivity requires the system to dissipate energy, that is: (3) This means that the passive judgment matrix of the system PIt is positive definite, meaning that the real parts of all its eigenvalues ​​remain non-negative. The above condition can be transformed into: (4) The above formula is the equivalent passive criterion for GFM converters, where A , B and F All are about frequency ω The function is denoted by . According to the passive property theory, an interconnected system composed of multiple passive subsystems must maintain its passive property. In a grid-connected system, the grid impedance is composed of passive components, and its passive property is necessarily true. Therefore, improving the control strategy can effectively expand the passive frequency band and increase the passive index, which has important guiding significance for enhancing the stability of converter grid-connected systems.

[0040] like Figure 2 The block diagram of the stability control strategy based on passive performance enhancement proposed in this invention simulates the frequency regulation characteristics of a synchronous generator and uses a virtual synchronous control (VSG) strategy to calculate the system phase. J and D p These represent the inertia coefficient and damping coefficient, respectively. n q This is the reactive power droop control coefficient.

[0041] According to the theory of passivity, Z qd and Z dq Coupling at low frequencies is a risk factor for low-frequency oscillations. Z qd Determined by virtual synchronization control, it corresponds to the effect of controller phase disturbance on the q-axis voltage signal through Park transformation in the inner loop control stage; Z dq Determined by reactive power droop control, it corresponds to the influence of electromotive force reference signal disturbance on the d-axis voltage reference signal in the inner loop control. Therefore, regarding the coupling terms in the converter output impedance matrix ( Z qd and Z dq To address the issue of disrupting the system's passivity, two compensation branches are designed in the inner-loop control loop to weaken the effect of coupling terms, including: A first additional branch (green background) is set up to compensate for the impact of controller phase disturbances on voltage control. This branch extracts the frequency disturbance signal from the synchronization link, filters the frequency disturbance signal through a high-pass filter, integrates it to obtain the controller phase disturbance, multiplies it by the electromotive force reference amplitude, and obtains the q-axis voltage compensation component. This compensation is then applied to the input terminal of the q-axis voltage control in the inner loop control loop (i.e., the q-axis voltage reference value). v qref(place), to weaken Z qd The impact on passivity; A second additional branch (red background) is set up to compensate for the impact of reactive power loop disturbances on voltage control. This branch extracts the reactive power error signal from the reactive power control loop, multiplies it by the reactive power droop control coefficient, and then processes it through a high-pass filter to obtain the d-axis electromotive force reference signal disturbance. This disturbance is then compensated to the input terminal of the d-axis voltage control in the inner loop control loop (i.e., the d-axis voltage reference value). v dref (place), to weaken Z dq The impact on passivity.

[0042] Specifically, the process of obtaining the d-axis electromotive force reference signal perturbation includes: Obtain the reactive power output of the converter Q o High-frequency noise is filtered out by a low-pass filter to obtain the reactive power after filtering. reactive power reference value Q ref Subtract the filtered reactive power, then multiply by the reactive power droop control factor. n q Then, the signal is processed by a high-pass filter to obtain the d-axis electromotive force reference signal perturbation.

[0043] The specific details of the d-axis electromotive force reference signal disturbance compensation to the input of the d-axis voltage control in the inner loop control loop are as follows: The PCC voltage reference signal controlled by the d-axis voltage of the inner loop control loop. v dref The d-axis electromotive force reference signal disturbance is subtracted for control.

[0044] The process of obtaining the q-axis voltage compensation component specifically includes: Obtain the active power output of the converter P o The active power reference value P ref Subtract the active power output of the converter P o The difference in active power is obtained. Subtract the feedback amount from the active power difference, and then divide by the virtual moment of inertia. J After integration, the frequency offset is obtained, and the feedback quantity is the frequency offset multiplied by the virtual damping coefficient. D p The result; The frequency offset is filtered by a high-pass filter and then integrated to obtain the controller phase disturbance. This controller phase disturbance is then multiplied by the electromotive force reference amplitude. E ref The q-axis voltage compensation component is obtained.

[0045] The q-axis voltage compensation component is specifically compensated to the input of the q-axis voltage control in the inner loop control loop as follows: The PCC voltage reference signal controlled by the q-axis voltage of the inner loop control loop. v qref The q-axis voltage compensation component is subtracted for control purposes.

[0046] like Figure 3 The diagram shows the low-frequency transfer mode of the GFM converter after adding stability enhancement control in this scheme. To avoid introducing new oscillation elements that could affect system stability, this scheme selects a first-order HPF to extract the disturbance signal. (See diagram.) G hpfd and G hpfq The HPF transfer function matrices for the d-axis and q-axis compensation branches are represented respectively, and their expressions are as follows: (5) In the formula, k hpf For branch road compensation coefficient, ω hpf The cutoff frequency is set to [value]. Considering both the control effect of the compensation branch and ensuring the HPF effectively extracts disturbance signals and filters out steady-state signals, in this embodiment, the cutoff frequency of the high-pass filter (HPF) is [value]. ω hpf The value is taken as 4π rad / s. Compensation coefficient. k hpf The value is 0.7.

[0047] like Figure 4 To demonstrate the improved converter output impedance after adding a compensation branch in this invention, the addition of the compensation branch... Z dd and Z qq It is only affected in the very low frequency range, and the phase remains within the positive resistance range; Z dq Under the action of compensation branch 2, the amplitude decreases while the phase remains almost unchanged; Z qd Under the effect of compensation branch 1, the amplitude is significantly reduced, and the phase exhibits a change of first lagging and then leading. Compared with the absence of compensation branch, the coupling terms of the converter output impedance are significantly reduced. Z qd and Zdq The amplitude is significantly reduced in the low-frequency range, and the negative resistance characteristic of the converter is significantly weakened.

[0048] like Figure 5 This demonstrates the improved passivity of the converter after adding a compensation branch in this invention. After adding the compensation branch, the system passivity criterion... A and B It is only affected in the extremely low frequency range, and still provides a damping effect; while the passive criterion index of the system F ( ω The frequency band increases significantly in the low-frequency range and decreases in the non-passive frequency range. Compared with the uncompensated range, the scheme eliminates the negative damping region above 20Hz, and the converter no longer has the risk of instability, thus significantly improving stability.

[0049] like Figure 6 (a) and (b) in the figure show the stability domain solutions for the grid-connected converter system with and without the compensation branch, respectively. Compared to the original system, the passive-enhanced stability control strategy proposed in this invention can significantly expand the stable operating range and achieve stable operation over a wider short-circuit ratio (SCR) range. Furthermore, after adopting the control strategy proposed in this invention, the selectable control parameters of the grid-connected converter ( J, D p The range of parameters (etc.) is wider, which reduces the burden of designing system control parameters and significantly improves control flexibility.

[0050] Compared to existing converter systems, the control strategy of this invention can significantly improve the passivity and stability of the system, and maximize the expansion of the system's stable operating range.

[0051] Example 2 This embodiment provides a control system for implementing a low-frequency stability control method for a grid-type converter based on passive performance enhancement as described in Embodiment 1. The grid-type converter includes interconnected DC current and AC circuits. The control system includes a synchronization link, a reactive power control link, a virtual impedance link, and an inner loop control link. The output of the virtual impedance link is connected to the inner loop control link. The outputs of the reactive power control link and the inner loop control link are both connected to the synchronization link. The outputs of the synchronization link and the inner loop control link control the AC circuit. The control system also includes: The first additional branch is used to extract the frequency disturbance signal from the synchronization link, filter the frequency disturbance signal through a high-pass filter and then integrate it to obtain the controller phase disturbance, and multiply it by the electromotive force reference amplitude to obtain the q-axis voltage compensation component, which is then compensated to the input terminal of the q-axis voltage control of the inner loop control link. The second additional branch is used to extract the reactive power error signal from the reactive power control loop, multiply it by the reactive power droop control coefficient, process it through a high-pass filter to obtain the d-axis electromotive force reference signal disturbance, and compensate it to the input terminal of the d-axis voltage control of the inner loop control loop.

[0052] The second additional branch includes: The d-axis electromotive force reference signal disturbance acquisition unit is used to extract the reactive power error signal from the reactive power control loop, multiply it by the reactive power droop control coefficient, and then process it through a high-pass filter to obtain the d-axis electromotive force reference signal disturbance. The d-axis voltage control compensation unit is used to compensate for disturbances in the d-axis electromotive force reference signal to the input terminal of the d-axis voltage control in the inner loop control loop.

[0053] The d-axis electromotive force reference signal disturbance acquisition unit specifically includes: Obtain the reactive power output of the converter Q o High-frequency noise is filtered out by a low-pass filter to obtain the reactive power after filtering. reactive power reference value Q ref Subtract the filtered reactive power, then multiply by the reactive power droop control factor. n q Then, the perturbation of the d-axis electromotive force reference signal is obtained by processing through a high-pass filter; The d-axis voltage control compensation unit is specifically as follows: The PCC voltage reference signal controlled by the d-axis voltage of the inner loop control loop. v dref The d-axis electromotive force reference signal disturbance is subtracted for control.

[0054] The second additional branch includes: The q-axis voltage compensation component acquisition unit is used to extract the frequency disturbance signal from the synchronization link, filter the frequency disturbance signal through a high-pass filter and then integrate it to obtain the controller phase disturbance, and multiply it by the electromotive force reference amplitude to obtain the q-axis voltage compensation component. The q-axis voltage control compensation unit is used to compensate the q-axis voltage compensation component to the input terminal of the q-axis voltage control of the inner loop control loop.

[0055] The q-axis voltage compensation component acquisition unit specifically includes: Obtain the active power output of the converter P o The active power reference value P ref Subtract the active power output of the converter P oThe difference in active power is obtained. Subtract the feedback amount from the active power difference, and then divide by the virtual moment of inertia. J After integration, the frequency offset is obtained, and the feedback quantity is the frequency offset multiplied by the virtual damping coefficient. D p The result; The frequency offset is filtered by a high-pass filter and then integrated to obtain the controller phase disturbance. This controller phase disturbance is then multiplied by the electromotive force reference amplitude. E ref The q-axis voltage compensation component is obtained; The q-axis voltage control compensation unit is specifically as follows: The PCC voltage reference signal controlled by the q-axis voltage of the inner loop control loop. v qref The q-axis voltage compensation component is subtracted for control purposes.

[0056] It should be noted that the specific content and beneficial effects of the system in this application can be found in the above method embodiments, and will not be repeated here.

[0057] Example 3 This embodiment provides a low-frequency stability control device for a grid-type converter based on passive enhancement, including a memory and a processor. The memory stores a computer program, and the processor calls the computer program to execute the steps of a low-frequency stability control method for a grid-type converter based on passive enhancement as described in Embodiment 1 above.

[0058] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of this application can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0059] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0060] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A low-frequency stability control method for a grid-type converter based on passive performance enhancement, wherein the grid-type converter includes interconnected DC current and AC circuits, and the control method for the grid-type converter includes a synchronization element, a reactive power control element, a virtual impedance element, and an inner loop control element; characterized in that The control method further includes: extracting a frequency disturbance signal from the synchronization link, filtering the frequency disturbance signal through a high-pass filter and integrating it to obtain the controller phase disturbance, multiplying it by the electromotive force reference amplitude to obtain the q-axis voltage compensation component, and compensating it to the input terminal of the q-axis voltage control of the inner loop control link; The reactive power error signal is extracted from the reactive power control loop, multiplied by the reactive power droop control coefficient, and then processed by a high-pass filter to obtain the d-axis electromotive force reference signal disturbance, which is then compensated to the input terminal of the d-axis voltage control of the inner loop control loop.

2. The low-frequency stability control method for a network-configuration type converter based on passive boost according to claim 1, characterized in that, The process of obtaining the d-axis electromotive force reference signal disturbance specifically includes: Obtaining reactive power of converter output Q o And through low-pass filter, high-frequency noise is filtered, and filtered reactive power is obtained. Reactive power reference value Q ref Subtract the filtered reactive power, then multiply by the reactive power droop control factor. n q Then, the signal is processed by a high-pass filter to obtain the d-axis electromotive force reference signal perturbation.

3. The low-frequency stability control method for a grid-type converter based on passive performance enhancement according to claim 1, characterized in that, The disturbance compensation of the d-axis electromotive force reference signal to the input terminal of the d-axis voltage control of the inner loop control loop is specifically as follows: The PCC voltage reference signal controlled by the d-axis voltage of the inner loop control loop. v dref The disturbance of the d-axis electromotive force reference signal is subtracted for control.

4. The low-frequency stability control method for a grid-type converter based on passive performance enhancement according to claim 1, characterized in that, The process of obtaining the q-axis voltage compensation component specifically includes: Obtain the active power output of the converter P o The active power reference value P ref Subtract the active power output of the converter P o The difference in active power is obtained. Subtract the feedback amount from the active power difference, and then divide by the virtual moment of inertia. J The frequency offset is then obtained by integration. The feedback quantity is the frequency offset multiplied by the virtual damping coefficient. D p The result; The frequency offset is filtered by a high-pass filter and then integrated to obtain the controller phase disturbance. This controller phase disturbance is then multiplied by the electromotive force reference amplitude. E ref The q-axis voltage compensation component is obtained.

5. The low-frequency stability control method for a grid-type converter based on passive performance enhancement according to claim 1, characterized in that, The q-axis voltage compensation component is specifically compensated to the input terminal of the q-axis voltage control of the inner loop control loop as follows: The PCC voltage reference signal controlled by the q-axis voltage of the inner loop control loop. v qref The q-axis voltage compensation component is subtracted for control purposes.

6. The low-frequency stability control method for a grid-type converter based on passive performance enhancement according to claim 1, characterized in that, The output of the virtual impedance link is connected to the inner loop control link, and the outputs of the reactive power control link and the inner loop control link are both connected to the synchronization link. The outputs of the synchronization link and the inner loop control link control the AC circuit.

7. The low-frequency stability control method for a grid-type converter based on passive performance enhancement according to claim 6, characterized in that, The synchronization mechanism adopts a method based on the active power output of the converter. P o The active power control or DC control based on a constant voltage source generates a phase signal for coordinate transformation of system voltage and current, thereby generating a control signal for the three-phase full-bridge inverter circuit of the AC circuit through PWM.

8. The low-frequency stability control method for a grid-type converter based on passive performance enhancement according to claim 6, characterized in that, The reactive power control circuit is based on the reactive power output of the converter. Q o Generate d-axis electromotive force reference signal e dref q-axis electromotive force reference signal e qref The value is given as 0.

9. The low-frequency stability control method for a grid-type converter based on passive performance enhancement according to claim 6, characterized in that, The virtual impedance element is used to convert the three-phase grid-connected current. i oabc dq components obtained after coordinate transformation i od and i oq All are achieved through the corresponding virtual resistors R v and inductance value L v The dq component of the PCC voltage reference signal is generated after performing virtual impedance calculation. v dref and v qref .

10. The low-frequency stability control method for a grid-type converter based on passive performance enhancement according to claim 1, characterized in that, The inner loop control circuit includes a voltage source and a current loop connected in sequence. The voltage source uses PI control to make the PCC voltage follow a reference value and outputs the dq component of the inductor current reference signal. i dref and i qref ; The current loop is based on the dq component of the inductor current reference signal. i dref and i qref By employing proportional control and combining it with the phase signal of the synchronization element for coordinate transformation, a three-phase modulated wave signal is ultimately output. v mabc .

11. A low-frequency stability control system for a grid-type converter based on passive performance enhancement, wherein the grid-type converter includes interconnected DC current and AC circuits; the control system includes a synchronization element, a reactive power control element, a virtual impedance element, and an inner-loop control element; characterized in that, The control system further includes: The first additional branch is used to extract the frequency disturbance signal from the synchronization link, filter the frequency disturbance signal through a high-pass filter and integrate it to obtain the controller phase disturbance, and multiply it by the electromotive force reference amplitude to obtain the q-axis voltage compensation component, which is then compensated to the input terminal of the q-axis voltage control of the inner loop control link. The second additional branch is used to extract the reactive power error signal from the reactive power control loop, multiply it by the reactive power droop control coefficient, process it through a high-pass filter to obtain the d-axis electromotive force reference signal disturbance, and compensate it to the input terminal of the d-axis voltage control of the inner loop control loop.

12. The low-frequency stability control system for a grid-type converter based on passive performance enhancement according to claim 11, characterized in that, The second additional branch includes: The d-axis electromotive force reference signal disturbance acquisition unit is used to extract the reactive power error signal from the reactive power control loop, multiply it by the reactive power droop control coefficient, and then process it through a high-pass filter to obtain the d-axis electromotive force reference signal disturbance. The d-axis voltage control compensation unit is used to compensate for the disturbance of the d-axis electromotive force reference signal to the input terminal of the d-axis voltage control of the inner loop control loop.

13. A low-frequency stability control system for a grid-type converter based on passive performance enhancement according to claim 12, characterized in that, The d-axis electromotive force reference signal disturbance acquisition unit specifically includes: Obtain the reactive power output of the converter Q o High-frequency noise is filtered out by a low-pass filter to obtain the filtered reactive power. Reactive power reference value Q ref Subtract the filtered reactive power, then multiply by the reactive power droop control factor. n q Then, the perturbation of the d-axis electromotive force reference signal is obtained by processing through a high-pass filter; The d-axis voltage control compensation unit is specifically as follows: The PCC voltage reference signal controlled by the d-axis voltage of the inner loop control loop. v dref The disturbance of the d-axis electromotive force reference signal is subtracted for control.

14. The low-frequency stability control system for a grid-type converter based on passive performance enhancement according to claim 11, characterized in that, The second additional branch includes: The q-axis voltage compensation component acquisition unit is used to extract the frequency disturbance signal from the synchronization link, filter the frequency disturbance signal through a high-pass filter and integrate it to obtain the controller phase disturbance, and multiply it by the electromotive force reference amplitude to obtain the q-axis voltage compensation component. The q-axis voltage control compensation unit is used to compensate the q-axis voltage compensation component to the input terminal of the q-axis voltage control of the inner loop control loop.

15. A low-frequency stability control system for a grid-type converter based on passive performance enhancement according to claim 14, characterized in that, The q-axis voltage compensation component acquisition unit specifically includes: Obtain the active power output of the converter P o The active power reference value P ref Subtract the active power output of the converter P o The difference in active power is obtained. Subtract the feedback amount from the active power difference, and then divide by the virtual moment of inertia. J The frequency offset is then obtained by integration. The feedback quantity is the frequency offset multiplied by the virtual damping coefficient. D p The result; The frequency offset is filtered by a high-pass filter and then integrated to obtain the controller phase disturbance. This controller phase disturbance is then multiplied by the electromotive force reference amplitude. E ref The q-axis voltage compensation component is obtained; The q-axis voltage control compensation unit is specifically as follows: The PCC voltage reference signal controlled by the q-axis voltage of the inner loop control loop. v qref The q-axis voltage compensation component is subtracted for control purposes.

16. A low-frequency stability control system for a grid-type converter based on passive performance enhancement according to claim 11, characterized in that, The output of the virtual impedance link is connected to the inner loop control link, and the outputs of the reactive power control link and the inner loop control link are both connected to the synchronization link. The outputs of the synchronization link and the inner loop control link control the AC circuit. The synchronization mechanism adopts a method based on the active power output of the converter. P o The active power control or DC control based on a constant voltage source generates a phase signal for coordinate transformation of system voltage and current, thereby generating a control signal for the three-phase full-bridge inverter circuit of the AC circuit through PWM.

17. A low-frequency stability control system for a grid-type converter based on passive performance enhancement as described in claim 16, characterized in that, The reactive power control circuit is based on the reactive power output of the converter. Q o Generate d-axis electromotive force reference signal e dref q-axis electromotive force reference signal e qref The value is given as 0.

18. A low-frequency stability control system for a grid-type converter based on passive performance enhancement according to claim 16, characterized in that, The virtual impedance element is used to convert the three-phase grid-connected current. i oabc dq components obtained after coordinate transformation i od and i oq All are achieved through the corresponding virtual resistors R v and inductance value L v The dq component of the PCC voltage reference signal is generated after performing virtual impedance calculation. v dref and v qref .

19. A low-frequency stability control system for a grid-type converter based on passive performance enhancement according to claim 16, characterized in that, The inner loop control circuit includes a voltage source and a current loop connected in sequence. The voltage source uses PI control to make the PCC voltage follow a reference value and outputs the dq component of the inductor current reference signal. i dref and i qref ; The current loop is based on the dq component of the inductor current reference signal. i dref and i qref By employing proportional control and combining it with the phase signal of the synchronization element for coordinate transformation, a three-phase modulated wave signal is ultimately output. v mabc .

20. A low-frequency stability control device for a grid-type converter based on passive performance enhancement, characterized in that, It includes a memory and a processor, wherein the memory stores a computer program, and the processor invokes the computer program to perform the steps of the method as described in any one of claims 1 to 10.

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