Converter additional control oscillation stability evaluation method and device

Abstract

This invention proposes a method and apparatus for evaluating the oscillation stability of an additional control loop in a converter. The invention includes: determining the control architecture of the converter grid-connected system; identifying the additional control loop that generates power regulation signals based on the rate of change of electrical parameters; constructing a first transfer function model characterizing the dynamic characteristics of the additional frequency control path; constructing a second transfer function model characterizing the dynamic characteristics of the additional voltage control path and taking into account the coupling effect of active power and voltage; obtaining the dominant oscillation frequency of the system; and determining the oscillation stability of the converter phase-locked loop (PLL) based on the phase characteristics of the first and second transfer function models at the dominant oscillation frequency. This invention can accurately evaluate the impact of additional fast frequency and voltage control on the oscillation stability of the PLL, improve the accuracy of small disturbance stability judgment of the converter PLL under weak grid conditions, and provide a reliable basis for control parameter tuning.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to a method and apparatus for evaluating the stability of converter additional control oscillations. Background Technology

[0002] With the development of new energy sources, the power system exhibits a "dual high" trend of high proportion of new energy and power electronic equipment, highlighting the characteristics of a weak power grid. As a core grid-connected device, the converter constructs an inertia and voltage support system through the coordinated operation of phase-locked loops, power control, and additional frequency and voltage support. Specifically, this control covers the entire process from frequency and voltage measurement to active and reactive power regulation, including phase-locked loop phase tracking and external power loop regulation.

[0003] However, existing methods for evaluating phase-locked loop (PLL) oscillations directly employ small disturbance analysis without taking into account the dynamics of the converter's additional fast-frequency voltage control. This may lead to amplification of the frequency and voltage change rate measurements due to system disturbances, or dynamic coupling of active and reactive currents causing PLL phase angle oscillations, thus affecting the accuracy of traditional PLL phase angle oscillation evaluation and making it difficult to assess the risk of PLL instability. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, the first objective of this invention is to propose a method for evaluating the stability of converter additional control oscillations.

[0006] Another objective of this invention is to provide a converter additional control oscillation stability evaluation device.

[0007] To achieve the above objectives, a first aspect of the present invention provides a method for evaluating the stability of additional control oscillations in a converter, comprising:

[0008] S1, Determine the control architecture of the converter grid-connected system and identify additional control links that generate power regulation signals based on the rate of change of electrical parameters; S2, Construct the first transfer function model that characterizes the dynamic properties of the additional frequency control path; S3, construct a second transfer function model that characterizes the dynamic characteristics of the additional voltage control path and takes into account the effects of active power and voltage coupling; S4. Obtain the dominant oscillation frequency of the system, and determine the oscillation stability of the converter phase-locked loop based on the phase characteristics of the first transfer function model and the second transfer function model at the dominant oscillation frequency.

[0009] In one embodiment of the present invention, determining the control architecture of the converter grid-connected system, and identifying additional control links that generate power regulation signals based on the rate of change of electrical parameters, includes: A cascaded control structure is constructed using grid voltage-oriented vector control, with additional frequency regulation and additional voltage regulation components set in the power control loop; The frequency deviation signal is filtered to generate a frequency change rate signal, which forms an additional value for active power regulation. The voltage deviation signal is filtered to generate a voltage change rate signal, which forms the reactive power regulation added value.

[0010] In one embodiment of the present invention, constructing a first transfer function model characterizing the dynamic characteristics of the additional frequency control path includes: Establish the phase-locked loop closed-loop transfer function to characterize the relationship between voltage phase angle disturbance and voltage phase angle deviation at the point of common coupling; Establish the transfer function of the filtering stage to characterize the correspondence between the frequency deviation signal and the frequency change rate signal; The first transfer function model is obtained by combining the phase-locked loop closed-loop transfer function, the filter stage transfer function, and the power control stage transfer function.

[0011] In one embodiment of the present invention, constructing a second transfer function model characterizing the dynamic characteristics of the additional voltage control path and taking into account the effects of active power and voltage coupling includes: Establish the transmission relationship between the voltage deviation at the point of common coupling and the reactive power regulation signal; establish the coupling relationship between changes in active current and changes in voltage amplitude; By combining the transmission relationship between voltage deviation and reactive power regulation signal, the coupling relationship between active power and voltage, and the transfer function of power control loop, the second transfer function model is obtained.

[0012] In one embodiment of the present invention, obtaining the dominant oscillation frequency of the system and determining the oscillation stability of the converter phase-locked loop based on the phase characteristics of the first transfer function model and the second transfer function model at the dominant oscillation frequency includes: Plot the frequency response curves of the first transfer function model and the second transfer function model, and analyze the influence of the filter parameters on the phase characteristics. The phase offset at the dominant oscillation frequency is compared with the preset phase threshold, and the impact of additional control on the oscillation stability of the phase-locked loop is determined based on the comparison results.

[0013] In one embodiment of the present invention, the preset phase threshold is ±180°. When the phase offset at the dominant oscillation frequency does not exceed the preset phase threshold, it is determined that the additional control can improve the oscillation stability of the phase-locked loop; when the phase offset exceeds the preset phase threshold, it is determined that the additional control will reduce the oscillation stability of the phase-locked loop.

[0014] In one embodiment of the present invention, constructing the first transfer function model includes: According to the formula Construct the closed-loop transfer function of the phase-locked loop, where This refers to the voltage phase angle disturbance measured by the phase-locked loop. According to the formula Construct the transfer function of the high-pass filter, where These are the proportional coefficient and the phase shift coefficient; According to the formula Generate the first transfer function model, where This is the transfer function model for the power outer loop PI control.

[0015] In one embodiment of the present invention, constructing the second transfer function model includes: According to the formula Construct the transfer function of the fast voltage-controlled high-pass filter, where , These are the proportional coefficient and the phase shift coefficient; According to the formula Construct the coupling relationship between the active current and the voltage amplitude; According to the formula Generate the second transfer function model, where Let be the transfer function of the fast voltage-controlled high-pass filter.

[0016] In one embodiment of the present invention, it further includes: When the phase shift coefficient of the high-pass filter is between 0.01s and 0.04s, the phase shift does not exceed [a certain value] at the dominant oscillation mode frequency of the system. It is determined that frequency control can improve the oscillation stability of the phase-locked loop; When the phase shift coefficient of the high-pass filter is between 0.05s and 0.1s, the phase shift exceeds [a certain value] at the dominant oscillation mode frequency of the system. It is determined that frequency control may worsen the oscillation stability of the phase-locked loop; When the phase shift coefficient of the high-pass filter is 0.01s or 0.02s, it is determined that fast voltage control helps improve the oscillation stability of the phase-locked loop; when the phase shift coefficient of the high-pass filter is 0.1s or 0.2s, it is determined that additional fast voltage control may worsen the oscillation stability of the phase-locked loop.

[0017] To achieve the above objectives, a second aspect of the present invention provides a converter additional control oscillation stability evaluation device, comprising: The architecture identification module is used to determine the control architecture of the converter grid-connected system and identify additional control links that generate power regulation signals based on the rate of change of electrical parameters. The first modeling module is used to construct the first transfer function model that characterizes the dynamic properties of the additional frequency control path. The second modeling module is used to construct a second transfer function model that characterizes the dynamic characteristics of the additional voltage control path and takes into account the effects of active power and voltage coupling. The stability determination module is used to obtain the dominant oscillation frequency of the system and determine the oscillation stability of the converter phase-locked loop based on the phase characteristics of the first transfer function model and the second transfer function model at the dominant oscillation frequency.

[0018] The present invention provides a method and apparatus for evaluating the oscillation stability of a converter with additional control, which can accurately evaluate the impact of the converter's additional fast frequency and voltage control on the oscillation stability of the phase-locked loop, improve the accuracy of traditional small disturbance stability judgment, and clarify the mechanism of the effect of control parameters on system stability.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] Figure 1 This is a flowchart of a converter additional control oscillation stability evaluation method according to an embodiment of the present invention; Figure 2 This is a diagram of a converter grid-connected system and its additional fast frequency and voltage control structure according to an embodiment of the present invention; Figure 3 This is a Bode plot of the fast frequency control transfer function Gdf according to an embodiment of the present invention; Figure 4 This is a Bode plot of the fast voltage control transfer function Gdv according to an embodiment of the present invention; Figure 5 This is a diagram of the active power disturbance of the converter under the influence of different delays in fast frequency control according to an embodiment of the present invention. Figure 6 This is a diagram showing the reactive power disturbance of the converter under different delay effects of fast voltage control according to an embodiment of the present invention. Figure 7 This is a structural diagram of a converter additional control oscillation stability evaluation device according to an embodiment of the present invention. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0023] The following description, with reference to the accompanying drawings, describes a method and apparatus for evaluating the oscillation stability of a converter under additional control, according to an embodiment of the present invention.

[0024] Figure 1 This is a flowchart of a converter additional control oscillation stability evaluation method according to an embodiment of the present invention, such as... Figure 1 As shown, it includes: S1, Determine the control architecture of the converter grid-connected system and identify additional control links that generate power regulation signals based on the rate of change of electrical parameters; Specifically, this step aims to clarify the system architecture and control logic of the object to be evaluated, laying the foundation for subsequent stability analysis. Specifically, it is necessary to confirm the overall control topology of the converter grid-connected system, focusing on identifying whether it includes an additional control loop that uses the rate of change of grid state variables to correct power commands. In this control structure, the system acquires grid frequency and voltage signals through a measurement unit, and generates frequency and voltage rate of change signals through signal processing. These signals are then mapped to additional reference values ​​for active and reactive power to achieve rapid grid support. As one implementation, the additional control loop may include a phase-locked loop (PLL) and a high-pass filter. The PLL tracks the voltage phase angle, and the high-pass filter extracts the rate of change component from the deviation signal; for example, the frequency control path may use a transfer function. The voltage control path uses a transfer function. This allows for the measurement of both frequency and voltage change rate. By clearly defining this structure, the key control paths affecting oscillation stability can be accurately identified.

[0025] This step, by pre-identifying additional fast control elements, ensures that the stability assessment method is applicable to converter systems with frequency and voltage support capabilities. It avoids the inaccuracy problem caused by traditional assessment methods neglecting additional control dynamics, and provides clear structural input for the subsequent construction of an accurate transfer function model.

[0026] S2, Construct the first transfer function model that characterizes the dynamic properties of the additional frequency control path; The purpose of constructing the first transfer function model is to quantify the impact of the frequency control path on system dynamics. Its core lies in establishing the mapping relationship between the voltage phase angle deviation at the point of common coupling and the additional active current. This model needs to cover the cascade characteristics of the phase-locked loop dynamics, signal filtering, and power control. By analyzing the frequency domain response of each functional module in the rate of change control loop, the transfer function characterizing the dynamic characteristics of this path is derived. As one implementation method, the first transfer function model can be specifically expressed as follows:

[0027] in, Let be the closed-loop transfer function of the phase-locked loop. Here is the transfer function of the high-pass filter. This is the power outer loop control transfer function. These are variables in the complex frequency domain. It should be noted that this modeling process is not limited to a specific filter order or controller type; any mathematical model that can characterize the response relationship between the phase angle deviation and the additional active current falls within the scope of this step.

[0028] By constructing this first transfer function model, the dynamic mechanism of additional fast frequency control acting on the phase-locked loop can be accurately revealed, a quantitative relationship can be established between the control parameters and the system stability, and a precise mathematical model basis can be provided for subsequent oscillation stability determination based on frequency domain characteristics, thereby improving the adaptability of the evaluation method to complex control dynamics and the accuracy of the evaluation results.

[0029] S3, construct a second transfer function model that characterizes the dynamic characteristics of the additional voltage control path and takes into account the effects of active power and voltage coupling; This step constructs a second transfer function model reflecting the dynamic characteristics of the voltage control path in the additional control loop. This model characterizes the response relationship between the point of common coupling voltage deviation and the additional reactive current, and considers the coupling effect of active current on voltage amplitude. By analyzing the transfer relationship between voltage deviation and the additional reactive reference value, and combining the power outer loop control characteristics, a dynamic model of reactive current relative to active current and voltage deviation is established. Considering the effect of grid-side equivalent circuit inductive reactance and current reference value on voltage fluctuations, the voltage coupling effect caused by active current changes is incorporated into the transfer function calculation. As one implementation method, the model is expressed as:

[0030] The coupling relationship between voltage deviation and active current can be analyzed as follows: This allows for the quantification of the coupling effect.

[0031] By constructing a second transfer function model that considers the coupling effect of active current on voltage amplitude, the mechanism by which fast voltage control affects the stability of the phase-locked loop (PLL) can be accurately quantified. This method overcomes the deficiency of neglecting the active-voltage coupling relationship in existing assessments, improves the accuracy of judging the oscillation stability of converter grid-connected systems, and provides a reliable basis for control parameter tuning.

[0032] S4. Obtain the dominant oscillation frequency of the system, and determine the oscillation stability of the converter phase-locked loop based on the phase characteristics of the first transfer function model and the second transfer function model at the dominant oscillation frequency.

[0033] This step aims to quantitatively evaluate the impact of additional control on the dynamics of the phase-locked loop (PLL) based on the established control path transfer function model. Specifically, firstly, the dominant oscillation mode frequency of the system under weak grid conditions is obtained, which characterizes the critical frequency at which the system is most prone to oscillation. Subsequently, the phase frequency characteristics of the first and second transfer function models at this frequency are calculated to obtain the phase offset introduced by the frequency control path and the voltage control path. The phase offset is compared with a preset phase threshold. If the phase offset causes the open-loop phase of the system to meet the critical condition of the negative feedback stability criterion, then the oscillation stability of the PLL is determined to be threatened. As one implementation method, the Bode plot of the transfer function can be plotted to observe whether the phase frequency characteristic curve exceeds the preset phase threshold at the dominant oscillation mode frequency, thereby determining whether the additional fast frequency and voltage control improves or worsens the oscillation stability of the system.

[0034] This step uses frequency domain analysis to transform complex time-domain dynamics into clear phase criteria, which can accurately identify the influence boundary of additional control parameters on the stability of the phase-locked loop. This avoids misjudgments caused by traditional evaluation methods ignoring rapid control dynamics, and improves the accuracy and reliability of oscillation stability evaluation.

[0035] In one embodiment of the present invention, the converter grid-connected system and its control structure are as follows: Figure 2 As shown, this system employs traditional grid voltage-oriented vector control to achieve three-level cascaded control. The additional fast frequency and voltage regulation control, i.e., df / dt control and dV / dt control, is implemented in the outer power control loop: the deviation signal between the frequency measured by the PLL and the reference value is used to generate RoCoF using a high-pass filter (HPF), thus forming an additional active power reference value; the voltage measurement unit obtains the deviation signal between the voltage and the rated value, which is then high-pass filtered to generate RoCoV, forming an additional reactive power reference value for the converter. Figure 2 The HPF contains Kdf&Kdv and Tdf&TdV, which are the scaling factor (Kdf&Kdv) and phase shift factor (Tdf&TdV) of the HPF, respectively.

[0036] Furthermore, to construct the transfer function model of the converter with additional fast frequency control, and to analyze the impact of fast frequency control (df / dt control) on stability, it is necessary to construct the transfer function of the phase angle deviation of the point of common coupling voltage (i.e., Δθv) on the additional active current (i.e., Δid). When the point of common coupling voltage is in per-unit value, the closed-loop transfer function of the phase-locked loop is as follows: (1) Where Δθpll is the voltage phase angle disturbance measured by the phase-locked loop, kppll and kppll are the proportional and integral coefficients of the PI control in the PLL control, respectively, s is the complex frequency domain variable, and Gpll is the PLL closed-loop transfer function. Therefore, the transfer functions of Δθv and Δid are: (2) Where GHPF_f is the HPF transfer function, as shown in the following formula, where Kdf and Tdf are the proportional coefficient and phase shift coefficient, respectively.

[0037] (3) GPI_pc is the power outer loop PI control transfer function model, as shown below, where kp_pc and ki_pc are the proportional and integral coefficients of the PI control.

[0038] (4) Furthermore, to construct the transfer function model of the converter's additional fast voltage control (dV / dt control) and analyze its impact on PLL stability, the transfer function of PCC voltage deviation versus additional reactive power reference value needs to be constructed as follows: (5) Where ΔUt is the PCC voltage deviation value, ΔQadd is the additional reactive signal reference value, and GHPF_V is the fast voltage control HPF transfer function, as shown below.

[0039] (6) Where Kdv and Tdv are the proportional coefficient and phase shift coefficient, respectively. Therefore, the transfer function between Δiq and Δid is: (7) in As shown in equation (5), As shown in equation (4). This indicates that when the PLL phase angle is disturbed, the fast frequency control causes a change in the converter output active current (Δid), which in turn causes a change in the PCC voltage (ΔUt) due to the active-voltage coupling relationship. This relationship can be analytically summarized as: (8) Where Xg is the thevenin equivalent inductive reactance of the grid side, idref0 is the reference value of the d-axis current of the current loop control, and Ug is the grid side voltage rating. In formula (5), it is represented by the transfer function Gd.

[0040] Furthermore, Bode plots of the transfer functions of fast frequency and voltage control were drawn to determine their impact on PLL stability. A linearized equation for the converter phase-locked loop at the equilibrium point without additional fast frequency and voltage control was constructed, and its small-disturbance stability was analyzed to obtain the dominant oscillation mode that appears as the short-circuit ratio decreases. Next, Bode plots of the fast frequency control transfer functions shown in equation (2) were drawn to observe the effects of different phase shift coefficients (Tdf) and proportional coefficients (Kdf) at different HPFs on the phase-frequency characteristic curve. It was analyzed whether the phase shift curve exceeded ±180° at the dominant oscillation mode frequency. If it exceeded, it was determined that the addition of fast frequency control might worsen the PLL oscillation stability; if it did not exceed, it was determined that the addition of fast frequency control might improve the PLL oscillation stability.

[0041] Similarly, plot the Bode plot of the fast voltage control transfer function shown in formula (7) and observe the effects of different phase shift coefficients (Tdv) and proportional coefficients (Kdv) on the phase frequency characteristic curves at different HPFs. Analyze whether the phase shift curve exceeds ±180° at the dominant oscillation mode frequency. If it exceeds, it is determined that the additional fast voltage control may worsen the oscillation stability of the PLL; if it does not exceed, it is determined that the additional fast voltage control may improve the oscillation stability of the PLL.

[0042] In one embodiment of the present invention, the target system structure and its control structure are defined according to... Figure 2 For the target system shown, the control method is defined. In this case, the converter control outer loop is selected to use active and reactive power control methods, and the control parameters are shown in Table 1.

[0043] Table 1

[0044] Furthermore, based on the parameters in Table 1, substitute them into the converter's additional fast frequency and voltage control transfer function model. Substituting the system and control parameters shown in Table 1 into the fast frequency control transfer function model, the following formula is obtained: (9) Where Gpll is the PLL closed-loop transfer function, as shown in the following formula.

[0045] (10) In formula (9), GHPF_f is the HPF transfer function, as shown in the following formula, where Kdf and Tdf are the proportional coefficient and phase shift coefficient, respectively.

[0046] (11) In formula (9), GPI_pc is the power outer loop PI control transfer function model, as shown below, where kp_pc and ki_pc are the proportional and integral coefficients of the PI control.

[0047] (12) Regarding voltage control, substituting the system and control parameters shown in Table 1 into the fast voltage control transfer function model, the result is shown in the following formula: (13) in It is represented by the transfer function Gd, as shown in the following formula.

[0048] (14) In formula (7) The function to pass to HPF is as follows: (15) In formula (7), GPI_pc is the power outer loop PI control transfer function model, as shown in formula (12).

[0049] Furthermore, Bode plots of the fast frequency and voltage control transfer functions were drawn to determine their impact on PLL stability. Next, the Bode plot of the fast frequency control transfer function shown in formula (9) was drawn, and different phase shift coefficients Tdf of the HPF were set to increase from 0.01s to 0.1s, as shown... Figure 3 As shown. Observe the effect of different phase shift coefficients (Tdf) at different HPFs on the phase frequency response curve. Analyze whether the phase shift curve exceeds ±180° at the dominant oscillation mode frequency. Figure 3 As shown, when Tdf is 0.01s~0.04s, the phase shift does not exceed ±180° at the dominant oscillation mode frequency (3~4Hz), indicating that frequency control can improve the oscillation stability of the PLL. When Tdf is 0.05s~0.1s, the phase shift exceeds ±180°, and frequency control may worsen the oscillation stability of the PLL.

[0050] Similarly, plot the Bode plot of the fast voltage control transfer function shown in formula (13) and observe the effect of different phase shift coefficients (Tdv) on the phase frequency response curves for different HPFs. Figure 4 As shown.

[0051] Furthermore, by Figure 4 It can be seen that when TdV = 0.01s or 0.02s, the phase shift does not exceed ±180° at the dominant oscillation mode frequency, indicating that fast voltage control helps improve the oscillation stability of the PLL. When TdV = 0.1s or 0.2s, the phase shift exceeds ±180°, indicating that additional fast voltage control may worsen the oscillation stability of the PLL.

[0052] Furthermore, simulation verification is performed to verify the above analysis. The simulation system is as follows: Figure 1 As shown, its parameters are shown in Table 1.

[0053] Furthermore, Figure 5 The dynamic performance of the active power deviation of the VSC output is demonstrated when the short-circuit ratio (SCR) decreases from 5 to 3 at 0 seconds. This performance is significantly affected by different time constants (Tdf) in conventional df / dt control. When using conventional df / dt control with Tdf = 0.01s, the damping characteristics of active power are improved. However, as Tdf increases, the stability improvement gradually deteriorates. Compared with the VSC system without df / dt control, the damping effect decreases at Tdf = 0.1s, which verifies the... Figure 3 The results of the Bode plot analysis are shown below.

[0054] Furthermore, Figure 6 The impact of RoCoV measurement delay on system stability was demonstrated. At 0 seconds, the short-circuit ratio (SCR) decreased from 5 to 3 to test the damping performance of the control strategy. Compared to a VSC system without dV / dt control, the conventional fast voltage control with TdV=0.01s effectively suppressed oscillations. However, as... Figure 5 As shown, when TdV increases to 0.1s, this control actually worsens the damping performance of the VSC system. This verifies... Figure 4 The results of the Bode plot analysis are shown below.

[0055] The embodiments of this invention also have the following technical effects: This invention proposes a method for evaluating the oscillation stability of a converter with added fast frequency and voltage control. A transfer function of fast frequency control on PLL stability is constructed. Furthermore, considering the coupling relationship between the converter output active power and the PCC voltage amplitude, a transfer function of the impact of added fast voltage control on PLL stability is constructed. Therefore, a method for judging the oscillation stability of the converter with added fast frequency and voltage control is proposed. A method for evaluating the oscillation stability of a converter with added fast frequency and voltage control is proposed; considering the coupling relationship between the converter output active power and the PCC voltage amplitude, a criterion for judging the impact of added fast voltage control on PLL stability is proposed.

[0056] To achieve the above embodiments, such as Figure 7 As shown, this embodiment also provides a converter additional control oscillation stability evaluation device 10, including: Architecture identification module 100 is used to determine the control architecture of the converter grid-connected system and identify additional control links that generate power regulation signals based on the rate of change of electrical parameters. The first modeling module 200 is used to construct a first transfer function model that characterizes the dynamic properties of the additional frequency control path. The second modeling module 300 is used to construct a second transfer function model that characterizes the dynamic characteristics of the additional voltage control path and takes into account the coupling effect between active power and voltage. The stability determination module 400 is used to obtain the dominant oscillation frequency of the system and determine the oscillation stability of the converter phase-locked loop based on the phase characteristics of the first transfer function model and the second transfer function model at the dominant oscillation frequency.

[0057] An embodiment of the present invention provides a converter additional control oscillation stability evaluation device, which can accurately evaluate the impact of converter additional fast frequency and voltage control on phase-locked loop oscillation stability, improve the accuracy of traditional small disturbance stability judgment, and clarify the mechanism of the effect of control parameters on system stability.

[0058] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0059] Furthermore, 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 technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

Claims

1. A method for evaluating oscillation stability of an additional control of a converter, characterized by, include: Determine the control architecture of the converter grid-connected system and identify additional control links that generate power regulation signals based on the rate of change of electrical parameters; Construct a first transfer function model that characterizes the dynamic properties of the additional frequency control path; Construct a second transfer function model that characterizes the dynamic characteristics of the additional voltage control path and takes into account the effects of active power and voltage coupling; The dominant oscillation frequency of the system is obtained, and the oscillation stability of the converter phase-locked loop is determined based on the phase characteristics of the first transfer function model and the second transfer function model at the dominant oscillation frequency.

2. The method of claim 1, wherein, The determination of the control architecture of the converter grid-connected system includes identifying additional control links that generate power regulation signals based on the rate of change of electrical parameters, including: A cascaded control structure is constructed using grid voltage-oriented vector control, with additional frequency regulation and additional voltage regulation components set in the power control loop; The frequency deviation signal is filtered to generate a frequency change rate signal, which forms an additional value for active power regulation. The voltage deviation signal is filtered to generate a voltage change rate signal, which forms the reactive power regulation added value.

3. The method of claim 1, wherein, The construction of the first transfer function model characterizing the dynamic characteristics of the additional frequency control path includes: Establish the phase-locked loop closed-loop transfer function to characterize the relationship between voltage phase angle disturbance and voltage phase angle deviation at the point of common coupling; Establish the transfer function of the filtering stage to characterize the correspondence between the frequency deviation signal and the frequency change rate signal; The first transfer function model is obtained by combining the phase-locked loop closed-loop transfer function, the filter stage transfer function, and the power control stage transfer function.

4. The method of claim 1, wherein, The construction of the second transfer function model, which characterizes the dynamic properties of the additional voltage control path and takes into account the coupling effect of active power and voltage, includes: Establish the transmission relationship between the voltage deviation at the point of common coupling and the reactive power regulation signal; establish the coupling relationship between changes in active current and changes in voltage amplitude; By combining the transmission relationship between voltage deviation and reactive power regulation signal, the coupling relationship between active power and voltage, and the transfer function of power control loop, the second transfer function model is obtained.

5. The method of claim 1, wherein, The process of obtaining the dominant oscillation frequency of the system, and determining the oscillation stability of the converter phase-locked loop based on the phase characteristics of the first and second transfer function models at the dominant oscillation frequency, includes: Plot the frequency response curves of the first transfer function model and the second transfer function model, and analyze the influence of the filter parameters on the phase characteristics. The phase offset at the dominant oscillation frequency is compared with the preset phase threshold, and the impact of additional control on the oscillation stability of the phase-locked loop is determined based on the comparison results.

6. The method of claim 5, wherein, The preset phase threshold is ±180°. When the phase offset at the dominant oscillation frequency does not exceed the preset phase threshold, it is determined that the additional control can improve the oscillation stability of the phase-locked loop. When the phase offset exceeds the preset phase threshold, it is determined that the additional control will reduce the oscillation stability of the phase-locked loop.

7. The method of claim 3, wherein, The constructing the first transfer function model comprises: according to formula Constructing the closed-loop transfer function of the phase-locked loop, wherein The voltage phase angle disturbance quantity measured for the phase-locked loop; According to the formula constructing the high-pass filter transfer function, wherein are a proportional coefficient and a phase shift coefficient; According to the formula generating the first transfer function model, wherein is a power outer loop PI control transfer function model.

8. The method of claim 4, wherein, The construction of the second transfer function model includes: According to the formula constructing the fast voltage-controlled high-pass filter transfer function, wherein , are a proportional factor and a phase-shift factor; According to the formula constructing the coupling relationship of the active current to the voltage amplitude; According to the formula generating the second transfer function model, wherein is the fast voltage control high pass filter transfer function.

9. The method of claim 7, wherein, The method further includes: When the high-pass filter phase shift coefficient is 0.01s to 0.04s, the phase shift at the system dominant oscillation mode frequency does not exceed , and it is determined that the frequency control can improve the phase-locked loop oscillation stability; When the high-pass filter phase shift coefficient is 0.05s to 0.1s, the phase shift at the system dominant oscillation mode frequency exceeds , determining that frequency control can deteriorate the phase-locked loop oscillation stability; When the phase shift coefficient of the high-pass filter is 0.01s or 0.02s, it is determined that fast voltage control helps improve the oscillation stability of the phase-locked loop; when the phase shift coefficient of the high-pass filter is 0.1s or 0.2s, it is determined that additional fast voltage control may worsen the oscillation stability of the phase-locked loop.

10. A converter additional control oscillation stability evaluation device characterized by comprising: include: The architecture identification module is used to determine the control architecture of the converter grid-connected system and identify additional control links that generate power regulation signals based on the rate of change of electrical parameters. The first modeling module is used to construct the first transfer function model that characterizes the dynamic properties of the additional frequency control path. The second modeling module is used to construct a second transfer function model that characterizes the dynamic characteristics of the additional voltage control path and takes into account the effects of active power and voltage coupling. The stability determination module is used to obtain the dominant oscillation frequency of the system and determine the oscillation stability of the converter phase-locked loop based on the phase characteristics of the first transfer function model and the second transfer function model at the dominant oscillation frequency.

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