阅读说明：本技术 基于模拟电阻控制的三相电压型整流器稳定性分析方法 (Three-phase voltage type rectifier stability analysis method based on analog resistance control ) 是由 韩华 吴振希 孙尧 林建亨 粟梅 于 2021-08-03 设计创作，主要内容包括：本公开实施例中提供了一种基于模拟电阻控制的三相电压型整流器稳定性分析方法,属于电学技术领域,具体包括：分析连接目标电网的整流器对应的初始回路；进行建模操作得到交流回路对应的第一频域表达式以及直流回路对应的第二频域表达式；联立第一频域表达式和第二频域表达式,得到小信号导纳模型；根据小信号导纳模型、电网阻抗模型和广义奈奎斯特准则,计算得到整流器的稳定区间。通过本公开的方案,在dq同步旋转坐标系下建立小信号导纳模型,基于三相整流器小信号导纳模型、电网阻抗模型和广义奈奎斯特判据,得到不同参数下系统稳定边界,分析不同参数对系统稳定性的影响,降低了建模难度和计算成本,提高了整流器的稳定性和鲁棒性。(The embodiment of the disclosure provides a three-phase voltage type rectifier stability analysis method based on analog resistance control, which belongs to the technical field of electricity and specifically comprises the following steps: analyzing an initial loop corresponding to a rectifier connected with a target power grid; carrying out modeling operation to obtain a first frequency domain expression corresponding to the alternating current loop and a second frequency domain expression corresponding to the direct current loop; the first frequency domain expression and the second frequency domain expression are combined to obtain a small signal admittance model; and calculating to obtain a stable interval of the rectifier according to the small signal admittance model, the power grid impedance model and the generalized Nyquist criterion. According to the scheme, the small-signal admittance model is established under the dq synchronous rotation coordinate system, the system stable boundary under different parameters is obtained based on the three-phase rectifier small-signal admittance model, the power grid impedance model and the generalized Nyquist criterion, the influence of the different parameters on the system stability is analyzed, the modeling difficulty and the calculation cost are reduced, and the stability and the robustness of the rectifier are improved.)

1. A three-phase voltage type rectifier stability analysis method based on analog resistance control is characterized by comprising the following steps:

analyzing an initial loop corresponding to a rectifier connected with a target power grid, wherein the initial loop comprises an alternating current loop and a direct current loop;

modeling the alternating current loop under a dq synchronous rotation coordinate system to obtain a first frequency domain expression corresponding to the alternating current loop, and modeling the direct current loop under the dq synchronous rotation coordinate system to obtain a second frequency domain expression corresponding to the direct current loop;

the first frequency domain expression and the second frequency domain expression are combined to obtain a small signal admittance model corresponding to the rectifier;

and calculating to obtain a stable interval of the rectifier according to the small signal admittance model, the power grid impedance model and the generalized Nyquist criterion.

2. The method of claim 1, wherein the step of modeling the ac loop under dq synchronous rotating coordinate system to obtain a first frequency domain expression corresponding to the ac loop comprises:

injecting small signal disturbance to the network side of the target power grid to obtain an input current time domain expression of the alternating current loop in the dq synchronous rotating coordinate system, and converting the input current time domain expression into an input current frequency domain expression;

and substituting the linearized current controller into the input current frequency domain expression to obtain the first frequency domain expression.

3. The method according to claim 1, wherein the step of performing modeling operation on the dc loop under the dq synchronous rotation coordinate system to obtain a second frequency domain expression corresponding to the dc loop comprises:

calculating an output voltage frequency domain expression of the direct current loop in the dq synchronous rotation coordinate system according to output and input power balance;

and substituting the linearized voltage loop controller into the output voltage frequency domain expression to obtain a second frequency domain expression.

4. The method of claim 1, wherein prior to the step of calculating a stability interval for the rectifier based on the small signal admittance model, the grid impedance model, and the generalized nyquist criterion, the method further comprises:

and establishing the power grid impedance model based on the weak electric property of the target power grid.

5. The method of claim 4, wherein the step of calculating a stability interval of the rectifier based on the small signal admittance model, the grid impedance model, and the generalized Nyquist criterion comprises:

obtaining an impedance ratio matrix according to the small signal admittance model and the power grid impedance model;

and calculating a stable interval of the rectifier according to the generalized Nyquist criterion and the impedance ratio matrix.

Technical Field

The embodiment of the disclosure relates to the field of electricity, in particular to a three-phase voltage type rectifier stability analysis method based on analog resistance control.

Background

Voltage source converters are currently finding more and more application in modern power systems incorporating renewable energy sources. The controllability of the power system is improved, and meanwhile, the stability problem caused by interaction of the rectifier and the power grid is more and more, so that the difficulty is brought to the operation of the rectifier. The voltage mode rectifier will oscillate when connected to a weak grid. Rectifiers using conventional double closed loop control may be unstable when connected to weak grids due to the influence of phase locked loop parameters. Furthermore, with double closed loop control, reactive control may affect the stability limit of the voltage mode rectifier. The analog resistance control of the analog rectification input end resistor is researched due to the advantage of good robustness, the voltage information of the common coupling point is not needed in the method, and the obtained stable domain range is not large enough. However, aiming at the advantages of good robustness, low cost and simpler realization of analog resistance control, the stability and the characteristics of the method in stability are not researched,

therefore, a three-phase voltage type rectifier stability analysis method based on analog resistance control, which is efficient, simple and convenient, and high in stability and robustness, is urgently needed.

Disclosure of Invention

In view of this, the embodiments of the present disclosure provide a method for analyzing stability of a three-phase voltage-type rectifier based on analog resistance control, which at least partially solves the problems of complex calculation, and poor stability and robustness in the prior art.

In a first aspect, an embodiment of the present disclosure provides a method for analyzing stability of a three-phase voltage-type rectifier based on analog resistance control, including:

analyzing an initial loop corresponding to a rectifier connected with a target power grid, wherein the initial loop comprises an alternating current loop and a direct current loop;

modeling the alternating current loop under a dq synchronous rotation coordinate system to obtain a first frequency domain expression corresponding to the alternating current loop, and modeling the direct current loop under the dq synchronous rotation coordinate system to obtain a second frequency domain expression corresponding to the direct current loop;

the first frequency domain expression and the second frequency domain expression are combined to obtain a small signal admittance model corresponding to the rectifier;

and calculating to obtain a stable interval of the rectifier according to the small signal admittance model, the power grid impedance model and the generalized Nyquist criterion.

According to a specific implementation manner of the embodiment of the present disclosure, the step of performing modeling operation on the ac loop under a dq synchronous rotation coordinate system to obtain a first frequency domain expression corresponding to the ac loop includes:

injecting small signal disturbance to the network side of the target power grid to obtain an input current time domain expression of the alternating current loop in the dq synchronous rotating coordinate system, and converting the input current time domain expression into an input current frequency domain expression;

and substituting the linearized current controller into the input current frequency domain expression to obtain the first frequency domain expression.

According to a specific implementation manner of the embodiment of the present disclosure, the step of performing modeling operation on the dc loop under the dq synchronous rotation coordinate system to obtain a second frequency domain expression corresponding to the dc loop includes:

calculating an output voltage frequency domain expression of the direct current loop in the dq synchronous rotation coordinate system according to output and input power balance;

and substituting the linearized voltage loop controller into the output voltage frequency domain expression to obtain a second frequency domain expression.

According to a specific implementation manner of the embodiment of the present disclosure, before the step of calculating the stable interval of the rectifier according to the small signal admittance model, the power grid impedance model and the generalized nyquist criterion, the method further includes:

and establishing the power grid impedance model based on the weak electric property of the target power grid.

According to a specific implementation manner of the embodiment of the present disclosure, the step of calculating a stable interval of the rectifier according to the small signal admittance model, the power grid impedance model and the generalized nyquist criterion includes:

obtaining an impedance ratio matrix according to the small signal admittance model and the power grid impedance model;

and calculating a stable interval of the rectifier according to the generalized Nyquist criterion and the impedance ratio matrix.

The three-phase voltage type rectifier stability analysis scheme based on analog resistance control in the embodiment of the disclosure includes: analyzing an initial loop corresponding to a rectifier connected with a target power grid, wherein the initial loop comprises an alternating current loop and a direct current loop; modeling the alternating current loop under a dq synchronous rotation coordinate system to obtain a first frequency domain expression corresponding to the alternating current loop, and modeling the direct current loop under the dq synchronous rotation coordinate system to obtain a second frequency domain expression corresponding to the direct current loop; the first frequency domain expression and the second frequency domain expression are combined to obtain a small signal admittance model corresponding to the rectifier; and calculating to obtain a stable interval of the rectifier according to the small signal admittance model, the power grid impedance model and the generalized Nyquist criterion.

The beneficial effects of the embodiment of the disclosure are: according to the scheme, the small signal admittance model of the three-phase voltage rectifier controlled by the analog resistor is established under the dq synchronous rotation coordinate system, the stable boundary of the system under different parameters is obtained based on the small signal admittance model of the three-phase rectifier, the power grid impedance model and the generalized Nyquist stability criterion, the influence of the different parameters on the stability of the system is analyzed, the modeling difficulty and the calculation cost are reduced, and the stability and the robustness of the rectifier are improved.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings needed to be used in the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present disclosure, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic flowchart of a method for analyzing stability of a three-phase voltage-type rectifier based on analog resistance control according to an embodiment of the present disclosure;

fig. 2 is a schematic diagram of a power grid-rectifier circuit involved in a method for analyzing stability of a three-phase voltage-type rectifier based on analog resistance control according to an embodiment of the present disclosure;

fig. 3 is a schematic diagram of a grid-rectifier circuit involved in another analog resistance control-based three-phase voltage-type rectifier stability analysis method provided in the embodiment of the present disclosure;

fig. 4 is a schematic diagram of a frequency sweep measurement result (Ydd) related to a method for analyzing stability of a three-phase voltage-type rectifier based on analog resistance control according to an embodiment of the present disclosure;

fig. 5 is a schematic diagram of a frequency sweep measurement result (Ydq) related to a method for analyzing stability of a three-phase voltage-type rectifier based on analog resistance control according to an embodiment of the present disclosure;

fig. 6 is a schematic diagram of a frequency sweep measurement result (Yqd) related to a method for analyzing stability of a three-phase voltage-type rectifier based on analog resistance control according to an embodiment of the present disclosure;

fig. 7 is a schematic diagram of a frequency sweep measurement result (Yqq) involved in another method for analyzing stability of a three-phase voltage-type rectifier based on analog resistance control according to an embodiment of the present disclosure;

fig. 8 is a nyquist diagram of different grid-side inductance values involved in the method for analyzing the stability of a three-phase voltage-type rectifier based on analog resistance control according to the embodiment of the present disclosure;

fig. 9 is a nyquist diagram of different filter inductance values involved in the method for analyzing stability of a three-phase voltage-type rectifier based on analog resistance control according to the embodiment of the disclosure;

fig. 10 is a nyquist diagram of the three-phase voltage-type rectifier stability analysis method based on analog resistance control according to the embodiment of the disclosure under different voltage loop control bandwidths;

fig. 11 is a graph illustrating that a network side inductance involved in the method for analyzing the stability of a three-phase voltage-type rectifier based on analog resistance control according to the embodiment of the present disclosure is L_gWhen the voltage is 26mH, the measurement result of the direct-current side voltage and the alternating-current input current is shown in a diagram;

fig. 12 is a graph illustrating that a network side inductance involved in a method for analyzing stability of a three-phase voltage-type rectifier based on analog resistance control according to an embodiment of the present disclosure is L_gWhen the voltage on the direct current side and the alternating current are 28mH, the measurement result is shown in a schematic diagram;

fig. 13 shows that the inductance of the grid side involved in the method for analyzing the stability of a three-phase voltage-type rectifier based on analog resistance control according to the embodiment of the present disclosure is L_fWhen the voltage is 20mH, the measurement result of the direct-current side voltage and the alternating-current input current is shown in a schematic diagram;

fig. 14 shows that the inductance of the grid side involved in the method for analyzing the stability of a three-phase voltage-type rectifier based on analog resistance control according to the embodiment of the present disclosure is L_fWhen the voltage is 22mH, the measurement result of the direct-current side voltage and the alternating-current input current is shown in a schematic diagram;

fig. 15 is a schematic diagram illustrating a result of an influence of a voltage loop control bandwidth on rectifier stability involved in a three-phase voltage-type rectifier stability analysis method based on analog resistance control according to an embodiment of the present disclosure.

Detailed Description

The embodiments of the present disclosure are described in detail below with reference to the accompanying drawings.

The embodiments of the present disclosure are described below with specific examples, and other advantages and effects of the present disclosure will be readily apparent to those skilled in the art from the disclosure in the specification. It is to be understood that the described embodiments are merely illustrative of some, and not restrictive, of the embodiments of the disclosure. The disclosure may be embodied or carried out in various other specific embodiments, and various modifications and changes may be made in the details within the description without departing from the spirit of the disclosure. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict. All other embodiments, which can be derived by a person skilled in the art from the embodiments disclosed herein without making any creative effort, shall fall within the protection scope of the present disclosure.

It is noted that various aspects of the embodiments are described below within the scope of the appended claims. It should be apparent that the aspects described herein may be embodied in a wide variety of forms and that any specific structure and/or function described herein is merely illustrative. Based on the disclosure, one skilled in the art should appreciate that one aspect described herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented and/or a method practiced using any number of the aspects set forth herein. Additionally, such an apparatus may be implemented and/or such a method may be practiced using other structure and/or functionality in addition to one or more of the aspects set forth herein.

It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present disclosure, and the drawings only show the components related to the present disclosure rather than the number, shape and size of the components in actual implementation, and the type, amount and ratio of the components in actual implementation may be changed arbitrarily, and the layout of the components may be more complicated.

In addition, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, it will be understood by those skilled in the art that the aspects may be practiced without these specific details.

In recent years, voltage source converters have found increasing application in modern power systems incorporating renewable energy sources. The controllability of the power system is improved, and meanwhile, the stability problem caused by interaction of the converter and the power grid is more and more, so that the difficulty is brought to the operation of the converter. Various studies have shown that voltage mode rectifiers oscillate when connected to a weak grid. Rectifiers using conventional double closed loop control may be unstable when connected to weak grids due to the influence of phase locked loop parameters. Furthermore, with double closed loop control, reactive control may affect the stability limit of the voltage mode rectifier.

In order to improve the stability of the system and further avoid the oscillation phenomenon caused by the instability of the small signal, it is necessary to analyze the stability of the small signal of the two controlled systems. The small signal stability analysis method is many. In recent years, some documents propose a state space stability analysis method for analyzing the stability of a system by calculating a characteristic value by a state space model. The method is advantageous for predicting the stability of the system by analyzing the eigenvalues of the state matrix. In addition, the method can also analyze the influence factors. However, the state space model requires all system parameters, which can be difficult to measure and acquire. Furthermore, when the system changes, the state space model needs to be reconstructed. Another approach is stability analysis based on impedance (admittance) modeling. The method is implemented by an impedance ratio determined by the grid impedance and the transformer admittance. This approach works even if the detailed parameters of the transducer are unknown, because the impedance (admittance) of the transducer can be obtained and verified by analytical modeling or measurement.

Currently, a grid-rectifier system stability analysis based on dual closed-loop control of impedance (admittance) modeling has been studied. In this approach, a phase-locked loop is typically required to achieve grid synchronization. In this method, a three-phase alternating current signal is converted into a direct current component in a dq coordinate system. Due to the influence of the phase-locked loop on the frequency domain characteristics, the dynamic characteristics of the phase-locked loop need to be considered. It can be easily seen that under the traditional double closed loop control, the admittance matrix of the grid-connected rectifiers is asymmetric. An asymmetric system may be represented by a multiple-input multiple-output transmission matrix. Thus, the generalized nyquist criterion can be used to analyze the stability of the grid-converter system. Because the impedance ratio is a matrix of 2 × 2, the transfer function matrix has two eigenvalues, and thus two nyquist curves can be drawn. Besides the generalized nyquist criterion, the determinant of the impedance ratio matrix can be derived to analyze the stability of the grid-connected converter.

However, aiming at other control strategies such as good robustness, low cost and simpler realization of analog resistance control, the stability and the characteristics of the method in stability are not researched, and aiming at a three-phase power grid-rectifier system based on analog resistance control, stability analysis based on impedance modeling is carried out in a dq coordinate system, so that the problem of small-signal impedance modeling of a three-phase voltage type rectifier under analog resistance control is solved, and the blank of converter grid-connected stability analysis based on analog resistance control is filled. This disclosure has analyzed the influence of net side inductance, filter inductance and control bandwidth to system stability, and system stability under with analog resistance control and the system stability under the control of traditional two closed loops have carried out contrastive analysis, the result shows, along with the inductance component increase of electric wire netting impedance, the system under two kinds of control all can become unstablely by stabilizing, nevertheless under the same and other control parameter of voltage loop bandwidth select the suitable circumstances, the system under the analog resistance control can bear bigger net side impedance, have wider stable domain when being connected with the light current net. In a certain range, along with the increase of the filter inductance, the system under the control of the analog resistance is changed from stable to unstable, and the system under the control of the double closed loops is changed from unstable to stable. With the increase of the voltage loop bandwidth, the systems under the two controls can be changed from stable to unstable, but the system under the control of the analog resistor can have higher voltage loop bandwidth

The embodiment of the disclosure provides a three-phase voltage type rectifier stability analysis method based on analog resistance control, and the method can be applied to a small signal stability analysis process in a scene that a voltage type rectifier is connected to a power grid, a new energy station and the like in a remote area.

Referring to fig. 1, a schematic flow chart of a method for analyzing stability of a three-phase voltage-type rectifier based on analog resistance control according to an embodiment of the present disclosure is shown. As shown in fig. 1, the method mainly comprises the following steps:

s101, analyzing an initial loop corresponding to a rectifier connected with a target power grid, wherein the initial loop comprises an alternating current loop and a direct current loop;

for example, when the application scenario is that a voltage-type rectifier is connected to a power grid in an area a, the stability of a small signal in the power grid in the area a needs to be analyzed, when the rectifier is connected to the target power grid, a circuit connection relationship is as shown in fig. 2 and 3, an initial loop corresponding to the rectifier connected to the target power grid may be analyzed, and then a three-phase rectifier system connected to the power grid may be divided into two loops, that is, the ac loop and the dc loop.

S102, carrying out modeling operation on the alternating current loop under a dq synchronous rotating coordinate system to obtain a first frequency domain expression corresponding to the alternating current loop, and carrying out modeling operation on the direct current loop under the dq synchronous rotating coordinate system to obtain a second frequency domain expression corresponding to the direct current loop;

in specific implementation, modeling operation needs to be performed on the alternating current loop under the dq synchronous rotation coordinate system, and modeling operation needs to be performed on the direct current loop under the dq synchronous rotation coordinate system, so that each parameter in the alternating current loop and each parameter in the direct current loop are calculated, and then a first frequency domain expression corresponding to the alternating current loop and a second frequency domain expression corresponding to the direct current loop are obtained, so that subsequent steps can be performed conveniently.

S103, the first frequency domain expression and the second frequency domain expression are combined to obtain a small signal admittance model corresponding to the rectifier;

in specific implementation, after the alternating current loop and the direct current loop are respectively modeled to obtain a first frequency domain expression corresponding to the alternating current loop and a second frequency domain expression corresponding to the direct current loop, the first frequency domain expression and the second frequency domain expression are combined to eliminate analog resistance, and finally, a frequency domain relational expression of input current and common coupling point voltage of the three-phase voltage type rectifier under the control of the analog resistance is obtained, so that an input admittance matrix of the rectifier can be obtained, and a small signal admittance model corresponding to the rectifier is formed.

Certainly, after the small-signal admittance model is obtained, frequency sweeping can be performed on the small-signal admittance model to verify the correctness and accuracy of admittance modeling of the three-phase voltage-type rectifier under the control of the analog resistor, as shown in fig. 4 to 10, the impedance measurement result is well matched with the established admittance model, and the correctness of admittance modeling of the three-phase voltage-type rectifier under the control of the analog resistor is proved.

And S104, calculating to obtain a stable interval of the rectifier according to the small signal admittance model, the power grid impedance model and the generalized Nyquist criterion.

In specific implementation, after the small signal admittance model is obtained, the influence of the power grid side inductance, the converter filter inductance and the voltage loop control bandwidth on the stability of the system is analyzed by combining the power grid impedance model and the generalized Nyquist criterion, so that the stable domain of the rectifier is obtained and is used as the stable interval output.

According to the method for analyzing the stability of the three-phase voltage type rectifier based on the analog resistance control, the small signal admittance model of the three-phase voltage rectifier controlled by the analog resistance is established under the dq synchronous rotation coordinate system, and the influence of the network side inductance, the filter inductance of the converter and the voltage loop control bandwidth on the system stability is analyzed based on the established small signal admittance model, the power grid impedance model and the generalized Nyquist stability criterion, so that the modeling difficulty and the calculation cost are reduced, and the stability and the robustness of the rectifier are improved.

On the basis of the foregoing embodiment, in step S102, performing modeling operation on the ac loop under the dq synchronous rotation coordinate system to obtain a first frequency domain expression corresponding to the ac loop includes:

injecting small signal disturbance to the network side of the target power grid to obtain an input current time domain expression of the alternating current loop in the dq synchronous rotating coordinate system, and converting the input current time domain expression into an input current frequency domain expression;

for example, sine waves with different values are sequentially input to the grid side of the target power grid as the small signal disturbance, and a time domain expression of an alternating-current side input current of a rectifier in a dq coordinate system is as follows:

wherein L is_fRepresenting the filter inductance, i, of the converter^cRepresenting the input current in dq coordinate system, E^cVoltage, v, representing point of common coupling in dq coordinate system^cRepresenting the rectifier input voltage in the dq coordinate system.

And substituting the linearized current controller into the input current frequency domain expression to obtain the first frequency domain expression.

In specific implementation, the current controller after linearization is substitutedThe input current Δ i can be obtained^cAnd a point of common coupling voltage Δ E^cAnd an analog resistance Δ r_eAnd then converting into the first frequency domain expression as follows:

wherein R is_eRepresenting the steady state value of the analog resistance, G_dA transfer function representing the dead band of the switch and the control delay.

Further, in step S102, performing modeling operation on the dc loop under the dq synchronous rotation coordinate system to obtain a second frequency domain expression corresponding to the dc loop, where the modeling operation includes:

calculating an output voltage frequency domain expression of the direct current loop in the dq synchronous rotation coordinate system according to output and input power balance;

in specific implementation, for the dc loop, the following may be obtained according to the output-input balance:wherein, C_dcIs a DC side capacitor, R_LIs a direct current side load, P is instantaneous active power,thereby obtaining the output voltage delta V of the direct current side_dcAnd a point of common coupling voltage Δ E^cAnd an analog resistance Δ r_eThe frequency domain relationship of (a) is as follows:

and substituting the linearized voltage loop controller into the output voltage frequency domain expression to obtain a second frequency domain expression.

After the output voltage frequency domain expression is obtained through calculation, the linearized voltage loop controller is substituted into the output voltage frequency domain expression to obtain the input current delta i^cAnd a point of common coupling voltage Δ E^cAnd an analog resistance Δ r_eAs the second frequency domain expression Δ r_e(s)＝F_dc(s)G₂(s)ΔE^c(s)+F_dc(s)H₂(s)Δi^c(s)。

On the basis of the foregoing embodiment, before calculating the stable interval of the rectifier according to the small signal admittance model, the grid impedance model and the generalized nyquist criterion in step S104, the method further includes:

and establishing the power grid impedance model based on the weak electric property of the target power grid.

In specific implementation, before analyzing the stability interval corresponding to the rectifier connected to the target power grid, a power grid impedance model corresponding to the target power grid needs to be calculated, and the power grid impedance model can be established based on the weak electric property of the target power grid.

Further, in step S104, calculating a stable interval of the rectifier according to the small signal admittance model, the power grid impedance model and the generalized nyquist criterion, including:

obtaining an impedance ratio matrix according to the small signal admittance model and the power grid impedance model;

and calculating a stable interval of the rectifier according to the generalized Nyquist criterion and the impedance ratio matrix.

Specifically, after the small signal admittance model and the power grid impedance model are obtained, the impedance ratio matrix may be obtained by multiplying the small signal admittance model, i.e., the input admittance matrix of the three-phase voltage-type rectifier controlled by the analog resistance, by the small signal admittance model of the power grid, as shown in fig. 11 to 15, and then the impedance ratio matrix is analyzed by using the generalized nyquist criterion for the influence of the power grid side inductance, the converter inductance, and the voltage loop control bandwidth on the stability, so as to obtain the stable critical value of the rectifier, and form the stable interval.

For example, as shown in fig. 11 and 12, the nyquist curve more easily encloses the (-1, j0) point and the system is less stable when the grid-side inductance is increased, i.e., the weaker the grid, when L_gAt 28mH or more, the Nyquist curve encloses the point (-1, j0), and the system begins to oscillate unstably. Specifically, when the network side inductance L_gWhen the voltage is 26mH, the voltage can stably track the set value 650V, the current is sinusoidal, and the system is stable; but the net side inductance increases to L_gAt 28mH, the voltage begins to oscillate, the current is distorted, the system is changed from stable to unstable, the accuracy of stability analysis is verified, and the stability boundary is at the inductance L_gAbout 28 mH.

As shown in fig. 13 and 14, the easier the nyquist curve surrounds the (-1, j0) point, the more unstable the system, when L is increased as the filter inductance of the rectifier is increased_gNot less than 28mH (in this case, the network side impedance is L)_g＝6mH，R_g0.0001 Ω), the nyquist curve encloses the point (-1, j0), and the system begins to oscillate destabilized. In particular, when the filter inductance L_fAt 20mH, the system is stable, but as the filter inductance increases to L_fWhen the voltage is 22mH, the voltage begins to oscillate, the current is distorted, the system is changed from stable to unstable, the accuracy of stability analysis is verified, and the stable boundary is at the filter inductance L_fAbout 22 mH.

As shown in FIG. 15, the easier the Nyquist curve is to wrap around (-1) as the control bandwidth of the voltage loop increasesJ0), the more unstable the system, when w_dAt 933rad/s or more, the Nyquist curve encloses a point of (-1, j0), and the system begins to oscillate unstably. Specifically, when the voltage loop bandwidth is limited by ω_d654rad/s is increased to w_dWhen the rate is 933rad/s, the system is changed from stable to unstable, the accuracy of stability analysis is verified, and the stable boundary is w_d933rad/s or so. The stable interval may be formed based on the above measurement results.

It should be understood that portions of the present disclosure may be implemented in hardware, software, firmware, or a combination thereof.

The above description is only for the specific embodiments of the present disclosure, but the scope of the present disclosure is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present disclosure should be covered within the scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the protection scope of the claims.