Method and device for judging stability of multi-bus type DC system based on bus admittance matrix

Abstract

The present invention discloses a method and device for determining the stability of a multi-bus DC system based on a bus admittance matrix. The present invention is applicable to a cascaded multi-bus DC system comprising k DC buses and k-1 DC transformers. The method is based on bus port impedance. A DC system with a single bus can be considered to be operating stably before being connected to the multi-bus DC system. The necessary and sufficient condition for the stability of the entire system is the bus admittance matrix Y bus The number of zeros in the right half plane of the determinant is 0. This criterion is not affected by the stability of the subsystem and can still effectively evaluate the stability of the multi-bus DC system when the subsystem is unstable. bus All elements in the system can be measured and obtained without knowing the detailed information and working status of each converter in the system. The entire system is a black box system, which can intuitively, conveniently and accurately judge the system stability.

Description

Technical Field

[0001] The invention discloses a multi-bus type DC system stability judgment method and device based on a bus admittance matrix, belonging to the technical field of power electronics. Background Art

[0002] With the rapid development of direct current (DC) transmission technology, multi-busbar DC systems have attracted widespread attention in applications such as power transmission, distributed energy access, and large-scale interconnection. Multi-busbar DC systems offer greater flexibility and reliability, effectively addressing complex grid structures and diverse power demands. However, as system scale increases, the parallel operation of multiple power electronic converters complicates the system's dynamic behavior. In particular, strong coupling between converters can cause busbar oscillations in the DC system.

[0003] To assess DC system stability, many researchers, both domestically and internationally, have pioneered impedance criteria for single-bus systems, such as impedance ratio, impedance sum, bus node impedance, and bus port impedance. These criteria have been used to assess the stability of various types of single-bus DC systems. As DC system architectures become increasingly complex, researchers have extended the impedance criteria used in single-bus systems to multi-bus DC systems. For multi-bus DC system assessments, ensuring that all converters can operate independently and stably can lead to misjudgments of impedance ratio, impedance sum, bus node impedance, and bus port impedance. This requires additional knowledge of the right-half-plane poles of some subsystems comprising the busbars. Furthermore, due to confidentiality agreements and user privacy concerns, some devices in the system behave as black-box systems, making it impossible to directly measure the exact right-half-plane poles of these subsystems. These methods are prone to misjudgments of stability. Without considering the stability of these subsystems, these methods, particularly the impedance ratio criterion, are only sufficient to determine system stability. In addition, the existing method directly uses the number of Nyquist curve circles without considering the influence of the integral term (1 / s). The existence of the integral term will affect the judgment of the number of Nyquist curve circles, which can easily cause system misjudgment and make the stability analysis process more complicated.

[0004] Therefore, there is an urgent need for a new criterion that can directly judge the stability of a multi-busbar "black box" DC distribution system without being affected by the integral term. Summary of the Invention

[0005] The present invention aims to provide a method and device for determining the stability of a multi-bus type DC system based on a bus admittance matrix, so as to solve the above technical problems.

[0006] The present invention adopts the following technical solutions to solve the above technical problems:

[0007] In a first aspect, the present invention provides a method for determining the stability of a multi-bus DC system based on a bus admittance matrix, wherein the multi-bus DC system includes k DC buses and k-1 DC transformers. The method is based on bus port impedance and specifically includes the following steps:

[0008] Based on the bus port characteristics of the converter, the converter on each DC bus is divided into two categories: an impedance Z-type converter and an admittance Y-type converter. Multiple impedance Z-type converters and admittance Y-type converters are connected in parallel on each DC bus. The multiple impedance Z-type converters and admittance Y-type converters can operate stably before being connected to a multi-bus DC system. The impedance Z-type converter is a converter whose bus port exhibits impedance characteristics, and the admittance Y-type converter is a converter whose bus port exhibits admittance characteristics.

[0009] By using the small signal models of Z-type converter and Y-type converter, the two-port small signal simplest model of multi-bus DC system is derived.

[0010] Obtaining the busbar admittance matrix by impedance measurement All elements of , construct the busbar admittance matrix;

[0011] By analyzing the determinant of the busbar admittance matrix The necessary and sufficient conditions for judging the stability of multi-bus DC systems are obtained: the determinant of the bus admittance matrix The number of zero points in the right half plane is zero;

[0012] According to the determinant of the busbar admittance matrix The amplitude and phase change trend of the Bode diagram is used to calculate the number of right half plane zeros of the bus admittance matrix of the multi-bus type DC system to be judged, and the determinant of the bus admittance matrix is ​​used The number of right half plane zeros The necessary and sufficient condition that is zero is used to determine the stability of the multi-bus DC system.

[0013] In one embodiment, the small signal models of the Z-type converter and the Y-type converter are used to derive a two-port small signal universal model of a multi-bus DC system. The specific method is as follows:

[0014] The Z-type and Y-type small signal models on the i-th DC bus are equivalent to a single bus impedance Z bus,i , based on the network structure, a two-port small signal simplest model of a multi-bus DC system is constructed to cope with the impedance measurement of various types of DC systems.

[0015] In one embodiment, the conditions for the independent stable operation of the impedance Z-type converter and the admittance Y-type converter are:

[0016] ,

[0017] in, represents the number of right half plane poles of the transfer function; represents the output impedance of the vth Z-type converter on the kth DC bus; represents the input admittance of the jth Y-type converter on the kth DC bus.

[0018] In one embodiment, the busbar admittance matrix is ​​obtained by the impedance measurement method. All elements of the busbar current disturbance are injected into the i-th busbar. , the impedance analyzer directly measures the impedance of the i-th bus ,pass Get the matrix self-admittance ;Measure the jth busbar ,pass Get matrix transadmittance .

[0019] In one embodiment, the busbar admittance matrix is ​​constructed for:

[0020] ,

[0021] Among them, the diagonal elements is the matrix self-admittance; the off-diagonal elements is the matrix mutual admittance.

[0022] In one embodiment, the calculation of the number of right half plane zeros of the bus admittance matrix of the multi-bus type DC system to be determined is specifically performed as follows:

[0023] The single-bus DC system contains multiple impedance Z-type converters and admittance Y-type converters. It operates stably before being connected to the multi-bus DC system, so it can be expressed as:

[0024] ,

[0025] Due to the impedance of a single bus There is no coexistence of right half plane zeros and poles, from The Bode plot amplitude at the anti-resonance point can be judged by the multiple of 90° phase drop. The number of right half plane zeros , the number of right half plane poles of the busbar admittance matrix Expressed as:

[0026] ,

[0027] The number of right half plane poles via the busbar admittance matrix Get the number of right half plane zeros of the busbar admittance matrix .

[0028] In one embodiment, the number of right half plane poles The equivalent impedance of a single bus The Bode plot of If there is a right half plane zero, an antiresonance point will appear. The number of right half plane poles can be directly obtained by the amplitude and phase changes at the antiresonance point of the Bode diagram, that is:

[0029]

[0030] in, and Expressed as the frequency points before and after resonance occurs; Indicates the change in the amplitude slope of the equivalent impedance of a single bus before and after resonance occurs; Indicates the phase change before and after the equivalent impedance resonance of a single busbar occurs.

[0031] In one embodiment, the number of right half plane zeros of the busbar admittance matrix is ​​expressed as:

[0032] ,

[0033] in, Indicates the change in the amplitude slope of the busbar admittance matrix before and after the determinant resonance occurs; It represents the phase change before and after the determinant resonance of the busbar admittance matrix occurs.

[0034] In a second aspect, the present invention provides a multi-bus type DC system stability judgment device based on a bus admittance matrix, the device comprising:

[0035] A converter classification module is configured to classify converters on each DC bus into two categories: impedance Z-type converters and admittance Y-type converters, based on converter port characteristics. Multiple impedance Z-type converters and admittance Y-type converters are connected in parallel on each DC bus. These multiple impedance Z-type converters and admittance Y-type converters are capable of stable operation before being connected to a multi-bus DC system.

[0036] A two-port small-signal minimalist model construction module is used to construct a two-port small-signal minimalist model based on a multi-bus DC system structure using the small-signal models of the Z-type converter and the Y-type converter;

[0037] Bus admittance matrix building module, used to obtain the bus admittance matrix through impedance measurement method All elements of , construct the busbar admittance matrix;

[0038] Stability criterion acquisition module, by analyzing the determinant of the busbar admittance matrix The necessary and sufficient conditions for the stability of multi-bus DC systems are obtained: the determinant of the bus admittance matrix The number of zero points in the right half plane is zero;

[0039] Evaluation and judgment module, based on the determinant of the busbar admittance matrix The amplitude and phase change trend of the Bode diagram is used to calculate the number of right half plane zeros of the bus admittance matrix of the multi-bus type DC system to be judged, and the determinant of the bus admittance matrix is ​​used The stability of the multi-bus DC system is judged based on the necessary and sufficient condition that the number of zero points in the right half plane is zero.

[0040] In a third aspect, the present invention provides a computer-readable storage medium having computer program instructions stored thereon, which, when executed by a processor, implement the above-mentioned multi-bus type DC system stability judgment method based on the bus admittance matrix.

[0041] Beneficial effects

[0042] (1) The proposed system stability criterion based on the bus admittance matrix is ​​applicable to cascaded multi-bus DC systems. The right half plane zero is determined by whether the amplitude and phase change trends in the Bode diagram are consistent. It is not affected by the integral term of the transfer function and is a necessary and sufficient condition for judging system stability.

[0043] (2) The criterion proposed in the present invention is based on bus port impedance, which is simple and easy to measure. It does not require internal information of the converter in the system or stability information of the subsystem, thus overcoming the limitations of existing criterion.

[0044] (3) The system stability criterion based on the bus admittance matrix can regard the multi-bus type DC system as a black box system. When the subsystem composed of some buses is unstable, the stability of the multi-bus type DC system can still be accurately evaluated by the impedance measurement method. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings, as part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention but do not constitute undue limitations thereon. Obviously, the drawings described below are merely examples, and those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0046] Figure 1 This is a topological diagram of a multi-bus DC system;

[0047] Figure 2A flow chart of a method for determining stability of a multi-bus DC system based on a bus admittance matrix provided by one embodiment of the present invention;

[0048] Figure 3 A two-port small signal model diagram of a multi-bus DC system provided by an embodiment of the present invention;

[0049] Figure 4 The simulation topology of an application example provided by an embodiment of the present invention;

[0050] Figure 5 A Bode diagram is provided in one embodiment of the present invention, wherein Figure 5 (a) Figure 5 (b) and Figure 5 (c) R L =7.2Ω 、 and Bode plot of

[0051] Figure 6 R provided by one embodiment of the present invention L =1.44 Ω and Bode plot of

[0052] Figure 7 A Bode diagram is provided for another embodiment of the present invention, wherein Figure 7 (a) Figure 7 (b) and Figure 7 (c) R L =1.44 Ω 、 and Bode plot of

[0053] Figure 8 R provided by one embodiment of the present invention L =7.2Ω 、 、 and Experimental waveform diagram;

[0054] Figure 9 R provided by one embodiment of the present invention L =1.44Ω in the subsystem composed of converters 2 and 3 、 and Experimental waveform diagram;

[0055] Figure 10 R provided by one embodiment of the present invention L =1.44Ω 、 、 and Experimental waveform diagram.

[0056] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but rather to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0057] In order to deepen the knowledge and understanding of the present invention, the technical solution of the present invention is further described below with reference to the accompanying drawings and specific implementation methods. The following embodiments are intended to explain the present invention but the present invention is not limited to the following embodiments.

[0058] The technical solution of the invention will be described in detail below with reference to the accompanying drawings, taking a multi-bus DC system as an example.

[0059] The topology of a multi-bus DC system is as follows: Figure 1 As shown in the figure, the multi-bus DC system includes k buses and k-1 DC transformers (DCTs). Multiple impedance Z-type converters and admittance Y-type converters are connected in parallel on each DC bus. Figure 1 In the figure, each DC bus is connected in parallel with M i Z-type converter and N i A Y-type converter.

[0060] The embodiment of the present invention provides a method for determining the stability of a multi-bus type DC system based on a bus admittance matrix. Figure 2 As shown in FIG, the method is based on bus port impedance and specifically includes the following steps:

[0061] Step S100: According to the port characteristics of the converter, the converter on each DC bus is divided into two categories: an impedance Z-type converter and an admittance Y-type converter. Multiple impedance Z-type converters and admittance Y-type converters are connected in parallel on each DC bus; the multiple impedance Z-type converters and admittance Y-type converters can operate stably before being connected to the multi-bus DC system.

[0062] In the embodiment of the present application, the impedance Z-type transformer is a transformer whose busbar port presents an impedance characteristic, and the admittance Y-type transformer is a transformer whose busbar port presents an admittance characteristic.

[0063] Furthermore, the conditions for the stable operation of the impedance Z-type converter and the admittance Y-type converter individually are:

[0064] (1)

[0065] in, Represents the number of right half-plane poles of the transfer function.

[0066] Step S200: Using the small signal models of the Z-type converter and the Y-type converter, the small signal models of the Z-type and Y-type on the i-th DC bus are equivalent to a single bus impedance. , thus constructing a two-port small-signal simplest model of a multi-bus DC system based on the network structure, making stability analysis simpler and providing a model basis for the implementation of impedance measurement methods to cope with impedance measurement of various types of DC systems;

[0067] Specifically, through the two-port small signal equivalent model, the two-port small signal general model of the multi-bus DC system can be obtained, such as Figure 3 As shown in the figure. is the system Norton equivalent current; is the port equivalent impedance of busbars 1,…,k; is the voltage of busbars 1,…,k; and are the input current and output current of the i-th (i=1, 2, …, k) DCT respectively; 、 、 and is the transfer function of the i-th DCT.

[0068] Step S300: Obtain the busbar admittance matrix by impedance measurement method All elements of , construct the busbar admittance matrix.

[0069] The busbar admittance matrix can be obtained by impedance measurement method All elements of , the specific method is:

[0070] Inject bus current disturbance on the i-th bus , the impedance analyzer directly measures the impedance of the i-th bus ,pass Get the matrix self-admittance Y bus,ii ;Measure the jth busbar ,pass Get the matrix self-admittance .

[0071] Further, the busbar admittance matrix is ​​constructed for:

[0072] (2)

[0073] Step S400: Analyze the determinant of the busbar admittance matrix The necessary and sufficient conditions for judging the stability of multi-bus DC systems are obtained: the determinant of the bus admittance matrix The number of right half plane zeros is zero.

[0074] According to classical control theory, the necessary and sufficient conditions for the stability of a multi-bus DC system are the determinant of the bus admittance matrix. There is no right half plane zero, that is

[0075] (3)

[0076] Therefore, the necessary and sufficient condition for the stability of multi-bus DC system is The number of right half plane zeros is zero.

[0077] Step S500: Based on the determinant of the busbar admittance matrix The amplitude and phase change trend of the Bode diagram is used to calculate the number of right half plane zeros of the bus admittance matrix of the multi-bus type DC system to be judged, and the determinant of the bus admittance matrix is ​​used The number of right half plane zeros The necessary and sufficient condition that is zero is used to determine the stability of the multi-bus DC system.

[0078] In the embodiment of the present application, M i Z-type converter and N i The single bus system of a Y-type converter is operating stably before being connected to the multi-bus DC system. The bus equivalent admittance is ,therefore

[0079] (4)

[0080] because There is no coexistence of right half plane zeros and poles, from The Bode plot amplitude at the anti-resonance point can be judged by the multiple of 90° phase drop. The number of right half plane poles , so the number of right half planes of the busbar admittance matrix is It can be expressed as:

[0081] (5)

[0082] From (5), we can see that It can be obtained by the Bode plot of a single Thevenin impedance, that is

[0083] (6)

[0084] in, and Expressed as the frequency points before and after resonance occurs; Indicates the change in the amplitude slope of the equivalent impedance of a single bus before and after resonance occurs; Indicates the phase change before and after the equivalent impedance resonance of a single busbar occurs.

[0085] Therefore, the number of RHP zeros in the busbar admittance matrix can be expressed as:

[0086] (7)

[0087] Therefore, the necessary and sufficient condition for the stability of the multi-bus DC system is (7) is zero, according to formulas (6) and (7), since There are no right half plane poles, so The number of right half plane poles can be calculated by substituting the amplitude and phase changes at the antiresonance point into formula (6). When there are no right half plane poles, The right half plane zero of The amplitude and phase change trends of the Bode diagram at the resonance point are directly obtained by substituting them into formula (7); when When there are right half plane poles, for possible adjacent right half plane zeros and poles, The amplitude and phase of the Bode diagram at the resonance point are substituted into formula (7) to obtain.

[0088] The stability of the DC power distribution system of the present invention can be determined by the bus admittance matrix Directly judge whether the number of zero points in the right half plane of the determinant is zero. The impedance analyzer is used to directly measure from the DC bus port, which is not affected by mode changes and does not require knowledge of the voltage or current source characteristics of each power electronic converter. The multi-bus DC system can be treated as a black box system, which is convenient for practical application.

[0089] The following example uses a simple three-stage cascaded DC system consisting of three Buck converters. Figure 4 As shown in the figure 、 、 and They are the switch tube, diode, inductor and capacitor of the converter; R L is the load resistance; 、 、 、 and are input voltage, bus voltage 1, bus voltage 2, load voltage and current; is the PI controller of converters 1, 2, and 3; is the transfer function of the PWM generator, and are the output current and input current at the bus terminals of the source converter and the load converter, respectively; is the bus voltage; is the output impedance of the i-th source converter; is the input impedance of the jth load converter; and is the system disturbance; and is the system response; Z bus is the busbar port impedance; R L is the load resistance; v in,1 、v bus,1 、v bus,2 、v o,3 and are input voltage, bus voltage 1, bus voltage 2, load voltage and current; G v,1,2,3 is the PI controller of converters 1, 2, and 3; G m,1,2,3 is the transfer function of the PWM generator.

[0090] The main parameters of the experimental system are shown in Table 1.

[0091] Table 1 Main experimental parameters

[0092]

[0093] Figure 5 Given R L =7.2Ω 、 and Bode diagram, as can be seen from the figure, 、 and The amplitude and phase change trends of , the DC system is stable.

[0094] Figure 6 Given R L =1.44Ω in the subsystem composed of converters 2 and 3 and Bode diagram, according to the impedance ratio criterion, and There is overlap at 860 Hz, the phase difference is greater than 180°, and the subsystem is unstable. Figure 7 Given R L =1.44 Ω 、 and The Bode plot of Figure 7 As can be seen from (a) and (b), and The amplitude and phase change trends of .from Figure 7 As can be seen in (c), there is an antiresonance point at 760 Hz, the amplitude increases, the phase decreases by about 180°, and there are two right-half-plane zeros on the surface. The system is unstable, and the oscillation frequency in the DC bus is about 760 Hz.

[0095] Figure 8 Given R L =7.2Ω 、 、 and Experimental waveform, from the figure we can see that the system is stable, Figure 5 The predicted results are consistent.

[0096] Figure 9 Given R L =1.44Ω when the main working waveform of the subsystem 、 and Experimental diagram, from the figure we can see that there is an oscillation of about 850Hz in the system, which is consistent with Figure 6 The forecast analysis results are basically consistent.

[0097] Figure 10 Given R L =1.44 Ω 、 、 and Experimental waveform. From the figure, we can see that there is an oscillation frequency of about 750 Hz in the system, which is consistent with Figure 7 The results are consistent with the prediction, which shows that the present invention is effective even when the subsystem is unstable.

[0098] In summary, the experiment verifies the stability criterion of a multi-bus DC system based on the bus admittance matrix of the present invention. The system stability can be determined by the bus admittance matrix. Determine whether the Bode curve has a right half plane zero.

[0099] In one embodiment, a multi-bus type DC system stability determination device based on a bus admittance matrix is ​​proposed, the device comprising:

[0100] A converter classification module is configured to classify converters on each DC bus into two categories: impedance Z-type converters and admittance Y-type converters, based on converter port characteristics. Multiple impedance Z-type converters and admittance Y-type converters are connected in parallel on each DC bus. These multiple impedance Z-type converters and admittance Y-type converters are capable of stable operation before being connected to a multi-bus DC system.

[0101] A two-port small-signal universal model construction module is used to derive a two-port small-signal universal model of a multi-bus DC system using the small-signal models of the Z-type converter and the Y-type converter;

[0102] Bus admittance matrix building module, used to obtain the bus admittance matrix through impedance measurement method All elements of , construct the busbar admittance matrix;

[0103] The necessary and sufficient condition acquisition module is used to obtain the determinant of the busbar admittance matrix The amplitude and phase variation trends of the Bode diagram are used to obtain the necessary and sufficient conditions for the stability of the multi-bus DC system: the determinant of the bus admittance matrix The number of zero points in the right half plane is zero;

[0104] The evaluation and judgment module is used to calculate the number of right half plane zeros of the bus admittance matrix of the multi-bus type DC system to be judged, and according to the determinant of the bus admittance matrix The stability of the multi-bus DC system is judged based on the necessary and sufficient condition that the number of zero points in the right half plane is zero.

[0105] It should be noted that the multi-bus type DC system stability judgment device based on the bus admittance matrix provided in the above embodiment only uses the division of the above functional modules as an example when executing the multi-bus type DC system stability judgment method based on the bus admittance matrix. In actual application, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the device can be divided into different functional modules to complete all or part of the functions described above. In addition, the multi-bus type DC system stability judgment device based on the bus admittance matrix provided in the above embodiment and the multi-bus type DC system stability judgment method based on the bus admittance matrix embodiment are of the same concept. The implementation process thereof is detailed in the multi-bus type DC system stability judgment method based on the bus admittance matrix embodiment, which will not be repeated here.

[0106] In one embodiment, a computer-readable storage medium is proposed. When the computer-readable instructions are executed by one or more processors, the one or more processors execute the steps of the above-mentioned multi-bus type DC system stability judgment method based on the bus admittance matrix. The steps include: dividing the converter on each DC bus into two categories: impedance Z-type converter and admittance Y-type converter according to the port characteristics of the converter, and connecting multiple impedance Z-type converters and admittance Y-type converters in parallel on each DC bus; the multiple impedance Z-type converters and admittance Y-type converters can operate stably before being connected to the multi-bus type DC system; using the small signal models of the Z-type converter and the Y-type converter, a two-port small signal universal model of the multi-bus type DC system is obtained; and obtaining the bus admittance matrix by an impedance measurement method. All elements of the busbar admittance matrix are constructed; by analyzing the determinant of the busbar admittance matrix The necessary and sufficient conditions for judging the stability of multi-bus DC systems are obtained: the determinant of the bus admittance matrix The number of zero points in the right half plane is zero; according to the determinant of the busbar admittance matrix The amplitude and phase change trend of the Bode diagram is used to calculate the number of right half plane zeros of the bus admittance matrix of the multi-bus type DC system to be judged, and the determinant of the bus admittance matrix is ​​used The number of right half plane zeros The necessary and sufficient condition that is zero is used to determine the stability of the multi-bus DC system.

[0107] Those skilled in the art will appreciate that all or part of the processes in the above-described method embodiments can be implemented by instructing related hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When executed, the program can include the processes in the above-described method embodiments. The aforementioned storage medium can be a non-volatile storage medium such as a magnetic disk, an optical disk, a read-only memory (ROM), or a random access memory (RAM).

[0108] In the description provided herein, numerous specific details are described. However, it is understood that embodiments of the present invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques are not shown in detail so as not to obscure the understanding of this description.

[0109] Furthermore, those skilled in the art will appreciate that, although some embodiments described herein include certain features included in other embodiments but not other features, combinations of features from different embodiments are also intended to fall within the scope of protection of the present invention and form different embodiments. For example, in the above embodiments, those skilled in the art will be able to use them in combination based on the known technical solutions and the technical problems to be solved by this application.

[0110] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with this patent can make slight changes or modifications to equivalent embodiments using the above-mentioned technical contents without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the solution of the present invention.

Claims

1. A method for determining the stability of a multi-bus DC system based on a bus admittance matrix, characterized in that: The multi-bus type DC system includes k DC buses and k-1 DC transformers. The method is based on bus port impedance and specifically includes the following steps: Based on the bus port characteristics of the converter, the converter on each DC bus is divided into two categories: an impedance Z-type converter and an admittance Y-type converter. Multiple impedance Z-type converters and admittance Y-type converters are connected in parallel on each DC bus. The multiple impedance Z-type converters and admittance Y-type converters can operate stably before being connected to a multi-bus DC system. The impedance Z-type converter is a converter whose bus port exhibits impedance characteristics, and the admittance Y-type converter is a converter whose bus port exhibits admittance characteristics. By using the small signal models of Z-type converter and Y-type converter, the two-port small signal simplest model of multi-bus DC system is derived. Obtaining the busbar admittance matrix by impedance measurement All elements of , construct the busbar admittance matrix; By analyzing the determinant of the busbar admittance matrix The necessary and sufficient conditions for judging the stability of multi-bus DC systems are obtained: the determinant of the bus admittance matrix The number of zero points in the right half plane is zero; According to the determinant of the busbar admittance matrix The amplitude and phase change trend of the Bode diagram is used to calculate the number of right half plane zeros of the bus admittance matrix of the multi-bus type DC system to be judged, and the determinant of the bus admittance matrix is ​​used The number of right half plane zeros The necessary and sufficient condition that the value of the sigma-thick DC system is zero is used to determine the stability of the multi-bus DC system. The busbar admittance matrix is ​​obtained by the impedance measurement method All elements of the busbar current disturbance are injected into the i-th busbar. , the impedance analyzer directly measures the impedance of the i-th bus ,pass Get the matrix self-admittance ;Measure the jth busbar ,pass Get matrix transadmittance , i≠j; The busbar admittance matrix is ​​constructed for: ， Among them, the diagonal elements is the matrix self-admittance; the off-diagonal elements is the matrix mutual admittance.

2. The method for determining the stability of a multi-bus type DC system based on a bus admittance matrix according to claim 1, characterized in that: The small signal models of the Z-type converter and the Y-type converter are used to obtain a two-port small signal universal model of a multi-bus DC system. The specific method is as follows: The Z-type and Y-type small signal models on the i-th DC bus are equivalent to a single bus impedance Z bus,i , based on the network structure, a two-port small signal simplest model of a multi-bus DC system is constructed to cope with the impedance measurement of various types of DC systems.

3. The method for determining the stability of a multi-bus DC system based on a bus admittance matrix according to claim 1, wherein: The conditions for the stable operation of the impedance Z-type converter and the admittance Y-type converter individually are: ， in, represents the number of right half plane poles of the transfer function; Indicates the k On the DC bus v The output impedance of a Z-type converter; Indicates the jth DC bus on the kth DC bus Y The input admittance of the converter.

4. The method for determining the stability of a multi-bus type DC system based on a bus admittance matrix according to claim 3, characterized in that: The specific method for calculating the number of right half plane zeros of the bus admittance matrix of the multi-bus type DC system to be determined is as follows: The single-bus DC system contains multiple impedance Z-type converters and admittance Y-type converters. It operates stably before being connected to the multi-bus DC system, so it can be expressed as: ， Due to the impedance of a single bus There is no right half plane zero and pole coexistence, from a single bus impedance The impedance of a single bus can be determined by the multiple of 90° phase drop at the anti-resonance point of the Bode plot amplitude. The number of right half plane zeros , the number of right half plane poles of the busbar admittance matrix Expressed as: ， The number of right half plane poles via the busbar admittance matrix Get the number of right half plane zeros of the busbar admittance matrix .

5. The method for determining the stability of a multi-bus type DC system based on a bus admittance matrix according to claim 4, characterized in that: The number of right half plane poles The equivalent impedance of a single bus The Bode plot of If there is a right half plane zero, an antiresonance point will appear. The number of right half plane poles can be directly obtained by the amplitude and phase changes at the antiresonance point of the Bode diagram, that is: ， in, and Expressed as the frequency points before and after resonance occurs; Indicates the change in the amplitude slope of the equivalent impedance of a single bus before and after resonance occurs; Indicates the phase change before and after the equivalent impedance resonance of a single busbar occurs.

6. The method for determining the stability of a multi-bus DC system based on a bus admittance matrix according to claim 5, characterized in that: The number of right half plane zeros of the busbar admittance matrix is ​​expressed as: ， in, Indicates the change in the amplitude slope of the busbar admittance matrix before and after the determinant resonance occurs; It represents the phase change before and after the determinant resonance of the busbar admittance matrix occurs.

7. A multi-bus type DC system stability judgment device based on bus admittance matrix, characterized in that: The device comprises: A converter classification module is configured to classify converters on each DC bus into two categories: impedance Z-type converters and admittance Y-type converters, based on converter port characteristics. Multiple impedance Z-type converters and admittance Y-type converters are connected in parallel on each DC bus. These multiple impedance Z-type converters and admittance Y-type converters are capable of stable operation before being connected to a multi-bus DC system. A two-port small-signal minimalist model construction module is used to construct a two-port small-signal minimalist model based on a multi-bus DC system structure using the small-signal models of the Z-type converter and the Y-type converter; Bus admittance matrix building module, used to obtain the bus admittance matrix through impedance measurement method All elements of , construct the busbar admittance matrix; Stability criterion acquisition module, by analyzing the determinant of the busbar admittance matrix The necessary and sufficient conditions for the stability of multi-bus DC systems are obtained: the determinant of the bus admittance matrix The number of zero points in the right half plane is zero; Evaluation and judgment module, based on the determinant of the busbar admittance matrix The amplitude and phase change trend of the Bode diagram is used to calculate the number of right half plane zeros of the bus admittance matrix of the multi-bus type DC system to be judged, and the determinant of the bus admittance matrix is ​​used The necessary and sufficient condition that the number of right half plane zeros is zero is used to determine the stability of the multi-bus DC system. The busbar admittance matrix is ​​obtained by the impedance measurement method All elements of the busbar current disturbance are injected into the i-th busbar. , the impedance analyzer directly measures the impedance of the i-th bus ,pass Get the matrix self-admittance ;Measure the jth busbar ,pass Get matrix transadmittance , ; The busbar admittance matrix is ​​constructed for: ， Among them, the diagonal elements is the matrix self-admittance; the off-diagonal elements is the matrix mutual admittance.

8. A computer-readable storage medium, characterized in that The computer-readable storage medium stores computer-readable instructions. When the computer-readable instructions are executed by one or more processors, the one or more processors execute the steps of the multi-bus type DC system stability judgment method based on the bus admittance matrix according to any one of claims 1 to 6.

Images