Method and device for judging stability of multi-bus direct current system based on bus admittance matrix

Abstract

The invention discloses a method and a device for judging the stability of a multi-bus direct-current system based on a bus admittance matrix, the method and the device are suitable for a cascade multi-bus direct-current system, the multi-bus direct-current system comprises k direct-current buses and k-1 direct-current transformers, and the method is based on bus port impedance. The direct-current system of a single bus can be regarded as stable operation before being connected to the multi-bus type direct-current system, and the necessary and sufficient condition for the stability of the whole system is that the number of zero points of the right half plane of a bus admittance matrix Ybus determinant is 0. The criterion is not influenced by the stability condition of the subsystem, and the stability of the multi-bus type direct current system can still be effectively evaluated when the subsystem is unstable. All elements in the bus admittance matrix Ybus can be obtained through measurement, detailed information and working states of all converters in the system do not need to be obtained, the whole system is a black box system, and the stability of the system can be visually, conveniently and accurately judged.

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 DC transmission technology, multi-bus DC systems have received extensive attention in applications such as power transmission, distributed energy access, and large-scale interconnection. Multi-bus DC systems have higher flexibility and reliability, and can effectively cope with complex grid structures and diverse power demands. However, as the scale of the system increases, the parallel operation of multiple power electronic converters makes the dynamic behavior of the system more complex, especially the strong coupling between the converters will cause bus oscillations in the DC system.

[0003] In order to evaluate the stability of DC systems, many scholars at home and abroad have taken the lead in proposing impedance criteria in single-bus systems, such as impedance ratio, impedance sum, bus node impedance criterion, bus port impedance criterion, etc., for the evaluation of the stability of various types of single-bus DC systems. With the increasing complexity of DC system architecture, relevant scholars have extended the impedance criterion based on single-bus systems to multi-bus DC systems. For the evaluation of multi-bus DC systems, the premise of ensuring that all converters can operate stably independently may cause misjudgment of impedance ratio, impedance sum, bus node impedance criterion, and bus port impedance criterion. It is necessary to know the right half plane pole situation of the subsystem composed of some buses as a potential premise. At the same time, due to confidentiality agreements and user privacy reasons, some devices in the system are black box systems. The accurate right half plane pole situation of the subsystem cannot be directly measured. The above methods are prone to misjudgment of stability. Without considering the stability of the subsystem, the above methods, especially the impedance ratio criterion, are only sufficient conditions for judging the stability of the system. In addition, the existing method directly uses the number of Nyquist curve encirclements 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 encirclements, 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-bus type “black box” DC distribution system without being affected by the integral term. Summary of the invention

[0005] The object of the present invention is 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 stability of a multi-bus type DC system based on a bus admittance matrix, wherein the multi-bus type DC system comprises k DC buses and k-1 DC transformers. The method is based on bus port impedance and specifically comprises the following steps:

[0008] According to the bus port characteristics of the converter, the converter on each DC bus is divided into two types: 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 presents an impedance characteristic, and the admittance Y-type converter is a converter whose bus port presents an admittance characteristic;

[0009] 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 obtained.

[0010] The bus admittance matrix Y is obtained by impedance measurement method bus All elements of the busbar admittance matrix are constructed;

[0011] By analyzing the determinant of the busbar admittance matrix det(Y bus ) characteristics, we can obtain the necessary and sufficient conditions for determining the stability of a multi-bus DC system: the determinant of the bus admittance matrix det(Y bus ) has zero right half plane zero points;

[0012] According to the determinant of the busbar admittance matrix det(Y bus ) of the Bode diagram, 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 det(Y bus ) 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 model of the Z-type converter and the Y-type converter is used to obtain a two-port small signal general model of a multi-bus DC system, and 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 , a two-port small signal simplest model of a multi-bus DC system is constructed according to the network structure to cope with the impedance measurement of various types of DC systems.

[0015] In one embodiment, the conditions for the impedance Z-type converter and the admittance Y-type converter to operate stably independently are:

[0016]

[0017] in, Represents the number of right half plane poles of the transfer function; Z oS,k,i represents the output impedance of the i-th Z-type converter on the k-th DC bus; Y iL,k,j represents the input admittance of the j-th Y-type converter on the k-th DC bus.

[0018] In one embodiment, the busbar admittance matrix Y is obtained by the impedance measurement method. bus The specific method is: inject bus current disturbance into 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 mutual admittance Y bus,ij (i≠j).

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

[0020]

[0021] Among them, the diagonal elements (Y bus,11 , Y bus,22 , …) is the matrix self-admittance; the off-diagonal elements (Y bus,12 , Y bus,21 , …) is the matrix mutual admittance.

[0022] In one implementation manner, 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] Since the single bus impedance Z bus,i There is no right half plane zero and pole coexistence, from Z bus,i The Bode plot amplitude at the anti-resonance point can be used to determine the multiple of 90° phase drop. bus,i The number of zeros in the right half plane Number of right half plane poles of busbar admittance matrix It is expressed as:

[0026]

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

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

[0029]

[0030] Among them, f osc+ and f osc- Expressed as the frequency points before and after resonance occurs; d|Z bus,i | / df| fosc+fosc- Indicates the change in the amplitude slope of the equivalent impedance of a single bus before and after resonance occurs; ∠Z bus,i | fosc+fosc- Indicates the phase change before and after the equivalent impedance resonance of a single bus.

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

[0032]

[0033] in, It represents the change of 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 used to classify the converters on each DC bus into two categories: impedance Z-type converters and admittance Y-type converters according to the port characteristics of the converters. 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.

[0036] A two-port small signal minimal model building module is used to build a two-port small signal minimal model according to 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 Y through impedance measurement method bus All elements of the busbar admittance matrix are constructed;

[0038] The stability criterion acquisition module analyzes the determinant of the busbar admittance matrix det(Y bus ) characteristics, we obtain the necessary and sufficient conditions for the stability of multi-bus DC systems: the determinant of the bus admittance matrix det(Y bus ) has zero right half plane zero points;

[0039] The evaluation module uses the determinant of the busbar admittance matrix det(Y bus ) of the Bode diagram, 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 det(Y bus ) is zero, which is a necessary and sufficient condition for judging the stability of the multi-bus DC system.

[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 point 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, does not require internal information of the converter in the system, and does not require 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 DC system as a black box system. When the subsystem composed of some buses is unstable, the stability of the multi-bus DC system can still be accurately evaluated by the impedance measurement method. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation of the present invention. Obviously, the accompanying drawings described below are only some embodiments. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

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

[0047] Figure 2 A flow chart of a method for determining stability of a multi-bus type DC system based on a bus admittance matrix provided by an 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 application example simulation topology 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 when Z o,1 , Z o,2 and det(Y bus )’s Bode plot;

[0051] Figure 6 R provided by an embodiment of the present invention L =1.44Ω is Z o,2 and Z in,3 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 =1.44Ω when Z o,1 , Z o,2 and det(Y bus )’s Bode plot;

[0053] Figure 8 R provided by an embodiment of the present invention L =7.2Ω when v bus,1 、v bus,2 、v o,3 and i o,3Experimental waveform diagram of

[0054] Fig. 9 R provided by an embodiment of the present invention L =1.44Ω, in the subsystem composed of converters 2 and 3, v bus,2 、v o,3 and i o,3 Experimental waveform diagram of

[0055] Fig.10 R provided by an embodiment of the present invention L =1.44Ω when v bus,1 、v bus,2 、v o,3 and i o,3 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 are intended 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 recognition and understanding of the present invention, the technical solution of the present invention is further introduced below in conjunction with the accompanying drawings and specific implementation methods. The following embodiments are explanations of the present invention and the present invention is not limited to the following embodiments.

[0058] The technical solution of the invention is described in detail below by taking a multi-bus type DC system as an example in conjunction with the accompanying drawings.

[0059] The topology of a multi-bus DC system is as follows: Figure 1 As shown in FIG. 1 , a 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 transformer 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, 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 a multi-bus DC system.

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

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

[0064]

[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 Z bus,i , thus constructing the simplest two-port small signal model of multi-bus DC system according to the network structure, making the stability analysis simpler and providing a model basis for the implementation of impedance measurement method 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; Y bus,1,…,k 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; Y iT,i , G vvT,i , G iiT,i and Z oT,i is the transfer function of the ith DCT.

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

[0069] The busbar admittance matrix Y can be obtained by impedance measurement method. bus 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 Y bus,ij , i≠j.

[0071] Further, construct the busbar admittance matrix Y bus for:

[0072]

[0073] Step S400: By analyzing the determinant of the busbar admittance matrix det(Y bus ) characteristics, we can obtain the necessary and sufficient conditions for determining the stability of a multi-bus DC system: the determinant of the bus admittance matrix det(Y bus ) has zero right half plane zero points.

[0074] According to classical control theory, the necessary and sufficient condition for the stability of a multi-bus DC system is the determinant of the bus admittance matrix det(Y bus ) has no zero point in the right half plane, that is

[0075]

[0076] Therefore, the necessary and sufficient condition for the stability of the multi-bus DC system is det(Y bus ) has zero right half plane zero points.

[0077] Step S500: According to the determinant det(Y bus ) of the Bode diagram, 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 det(Y bus ) 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 transformer and N i The single bus system with a Y-type converter is running stably before being connected to the multi-bus DC system. The bus equivalent admittance is Y bus,i ,therefore

[0079]

[0080] Because Z bus,iThere is no right half plane zero and pole coexistence, from Z bus,i The Bode plot amplitude at the anti-resonance point can be used to determine the multiple of 90° phase drop. bus,i The number of right half plane poles Therefore, the number of right half planes of the busbar admittance matrix is It can be expressed as:

[0081]

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

[0083]

[0084] Among them, f osc+ and f osc- Expressed as the frequency points before and after resonance occurs; d|Z bus,i | / df| fosc+fosc- Indicates the change in the amplitude slope of the equivalent impedance of a single bus before and after resonance occurs; ∠Z bus,i | fosc+fosc- Indicates the phase change before and after the equivalent impedance resonance of a single bus.

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

[0086]

[0087] in, It represents the change of 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.

[0088] Therefore, the necessary and sufficient condition for the stability of a multi-bus DC system is is zero, according to formulas (6) and (7), since Z bus,i There is no right half plane pole, so det(Y bus ) can be calculated by substituting the amplitude and phase changes at the anti-resonance point into formula (6). bus ) does not exist in the right half plane, det(Y bus ) can be obtained by det(Y bus )'s Bode diagram at the resonance point, the amplitude and phase change trend are directly obtained by substituting it into formula (7); when det(Y bus ) has a right half plane pole, for possible adjacent right half plane zeros and poles, det(Y bus) at the resonance point is substituted into formula (7) to obtain the amplitude and phase of the Bode diagram.

[0089] The stability of the DC power distribution system of the present invention can be obtained by the bus admittance matrix Y bus Directly judge whether the number of zero points in the right half plane of the determinant is zero. bus The impedance analyzer is used to directly measure from the DC bus port, which is not affected by mode changes and does not require knowing 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.

[0090] The following example uses a simple three-stage cascaded DC system consisting of three Buck converters in cascade. Figure 4 As shown in the figure, Q x , D x , L x and C x (x=1,2,3) are the switch tube, diode, inductor and capacitor of the converter respectively; R L is the load resistance; v in,1 、v bus,1 、v bus,2 、v o,3 and i o,3 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, I bus_vi and I bus_ci are the output current and input current of the bus terminal of the source converter and the load converter respectively; V bus is the bus voltage; Z oSi is the output impedance of the ith source converter; Y iLj is the input impedance of the jth load converter; and is the system disturbance; and is the system response; Z bus is the bus port impedance; R L is the load resistance; v in,1 、v bus,1 、v bus,2 、v o,3 and i o,3 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.

[0091] The main parameters of the experimental system are shown in Table 1.

[0092] Table 1 Main parameters of the experiment

[0093]

[0094] Figure 5 Given R L =7.2Ω when Z o,1 , Z o,2 and det(Y bus ) of the Bode diagram. From the figure, we can see that Z o,1 , Z o,2 and det(Y bus ) has the same amplitude and phase change trend, so The DC system is stable.

[0095] Figure 6 Given R L =1.44Ω, Z in the subsystem composed of converters 2 and 3 o,2 and Z in,3 Bode plot, according to the impedance ratio criterion, Z o,2 and Z in,3 There is overlap at 860Hz, the phase difference is greater than 180°, and the subsystem is unstable. Figure 7 Given R L =1.44Ω when Z o,1 , Z o,2 and det(Y bus )'s Bode plot, from Figure 7 As can be seen from (a) and (b), Z o,1 and Z o,2 The amplitude and phase change trends of from Figure 7 As can be seen in (c), there is an anti-resonance point at 760 Hz, the amplitude increases, the phase decreases by about 180°, 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.

[0096] Figure 8 Given R L =7.2Ω when v bus,1 、v bus,2 、v o,3 and i o,3 Experimental waveform diagram, from which we can see that the system is stable, Figure 5 The predicted results are consistent.

[0097] Fig. 9 Given R L =1.44Ω when the main working waveform of the subsystem vbus,2 、v o,3 and i o,3 Experimental diagram. From the diagram, we can see that there is an oscillation of about 850Hz in the system. Figure 6 The forecast analysis results are basically consistent.

[0098] Fig.10 Given R L =1.44Ω when v bus,1 、v bus,2 、v o,3 and i o,3 Experimental waveform diagram. From the figure, we can see that there is an oscillation frequency of about 750Hz in the system, which is Figure 7 The results are consistent with the predictions, indicating that the present invention is effective even when the subsystem is unstable.

[0099] 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 Y bus Determine whether the Bode curve has a right half-plane zero.

[0100] In one embodiment, a multi-bus type DC system stability judgment device based on a bus admittance matrix is ​​proposed, the device comprising:

[0101] A converter classification module is used to classify the converters on each DC bus into two categories: impedance Z-type converters and admittance Y-type converters according to the port characteristics of the converters. 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.

[0102] A two-port small-signal general model building module is used to obtain a two-port small-signal general model of a multi-bus DC system using the small-signal models of the Z-type converter and the Y-type converter;

[0103] Bus admittance matrix building module, used to obtain the bus admittance matrix Y through impedance measurement method bus All elements of the busbar admittance matrix are constructed;

[0104] The necessary and sufficient condition acquisition module is used to obtain the determinant of the busbar admittance matrix det(Y bus ) of the Bode diagram, the necessary and sufficient conditions for the stability of the multi-bus DC system are obtained: the determinant of the bus admittance matrix det(Y bus ) has zero right half plane zero points;

[0105] 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 det(Y bus ) is zero, which is a necessary and sufficient condition for judging the stability of the multi-bus DC system.

[0106] 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 applications, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the device is 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 belong to 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.

[0107] In one embodiment, a computer-readable storage medium is proposed, and 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 comprising: according to the port characteristics of the converter, the converter on each DC bus is divided into two categories: impedance Z-type converter and admittance Y-type converter, and each DC bus is connected in parallel with a plurality of impedance Z-type converters and admittance Y-type converters; the plurality of 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 model of the Z-type converter and the Y-type converter, a two-port small signal general model of the multi-bus type DC system is obtained; the bus admittance matrix Y is obtained by an impedance measurement method. bus All elements of the busbar admittance matrix are constructed; by analyzing the determinant of the busbar admittance matrix det(Y bus ) characteristics, we can obtain the necessary and sufficient conditions for determining the stability of a multi-bus DC system: the determinant of the bus admittance matrix det(Y bus ) has zero points in the right half plane; according to the determinant of the busbar admittance matrix det(Y bus ) of the Bode diagram, 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 det(Y bus ) The necessary and sufficient condition that is zero is used to determine the stability of the multi-bus DC system.

[0108] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program, and the computer program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, the aforementioned storage medium can be a non-volatile storage medium such as a disk, an optical disk, a read-only memory (ROM), or a random access memory (RAM).

[0109] In the description provided herein, a large number of specific details are described. However, it is understood that embodiments of the present invention can 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.

[0110] In addition, those skilled in the art will understand that, although some embodiments described herein include certain features included in other embodiments but not other features, the combination of features of different embodiments also means being within the scope of protection of the present invention and forming different embodiments. For example, in the above embodiments, those skilled in the art can use them in combination according to the known technical solutions and the technical problems to be solved by this application.

[0111] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this patent can make some changes or modify the technical contents suggested above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the solution of the present invention.

Claims

1. A method for determining stability of a multi-bus type DC system based on a bus admittance matrix, characterized in that: The multi-bus type DC system comprises k DC buses and k-1 DC transformers. The method is based on bus port impedance and specifically comprises the following steps: According to the bus port characteristics of the converter, the converter on each DC bus is divided into two types: 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 presents an impedance characteristic, and the admittance Y-type converter is a converter whose bus port presents an admittance characteristic; 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 obtained. The bus admittance matrix Y is obtained by impedance measurement method bus All elements of the busbar admittance matrix are constructed; By analyzing the determinant of the busbar admittance matrix det(Y bus ) characteristics, we can obtain the necessary and sufficient conditions for determining the stability of a multi-bus DC system: the determinant of the bus admittance matrix det(Y bus ) has zero right half plane zero points; According to the determinant of the busbar admittance matrix det(Y bus ) of the Bode diagram, 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 det(Y bus ) The necessary and sufficient condition that is zero is used to determine the stability of the multi-bus DC system.

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

3. The method for determining stability of a multi-bus type DC system based on a bus admittance matrix according to claim 1, characterized in that: The conditions for the impedance Z-type converter and the admittance Y-type converter to operate stably independently are: in, Represents the number of right half plane poles of the transfer function; Z oS,k,i represents the output impedance of the i-th Z-type converter on the k-th DC bus; Y iL,k,j represents the input admittance of the j-th Y-type converter on the k-th DC bus.

4. The method for determining stability of a multi-bus type DC system based on a bus admittance matrix according to claim 1, characterized in that: The busbar admittance matrix Y is obtained by the impedance measurement method bus The specific method is: inject bus current disturbance into 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 mutual admittance Y bus,ij (i≠j).

5. The method for determining stability of a multi-bus type DC system based on a bus admittance matrix according to claim 4, characterized in that: The busbar admittance matrix Y is constructed bus for: Among them, the diagonal elements (Y bus,11 , Y bus,22 , …) is the matrix self-admittance; the off-diagonal elements (Y bus,12 , Y bus,21 , …) is the matrix mutual admittance.

6. The method for determining 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: Since the single bus impedance Z bus,i There is no right half plane zero and pole coexistence, from a single bus impedance Z bus,i The impedance Z of a single bus can be determined by the multiple of 90° phase drop at the anti-resonance point of the Bode plot amplitude. bus,i The number of zeros in the right half plane Number of right half plane poles of busbar admittance matrix It is expressed as: The number of right half plane poles via the bus admittance matrix Get the number of right half plane zeros of the busbar admittance matrix 7. The method for determining stability of a multi-bus type DC system based on a bus admittance matrix according to claim 6, characterized in that: The number of right half plane poles The equivalent impedance Z of a single busbar can be bus,i The Bode plot of Z bus,i If there is a right half plane zero, an anti-resonance point will appear. The number of right half plane poles can be directly obtained by the amplitude and phase changes at the anti-resonance point of the Bode diagram, that is: Among them, f osc+ and f osc- Expressed as the frequency points before and after resonance occurs; d|Z bus,i | / df| fosc+fosc- Indicates the change in the amplitude slope of the equivalent impedance of a single bus before and after resonance occurs; ∠Z bus,i | fosc+fosc- Indicates the phase change before and after the equivalent impedance resonance of a single bus.

8. The method for determining stability of a multi-bus type DC system based on a bus admittance matrix according to claim 7, characterized in that: The number of right half plane zeros of the busbar admittance matrix is ​​expressed as: in, It represents the change of 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.

9. 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 used to classify the converters on each DC bus into two categories: impedance Z-type converters and admittance Y-type converters according to the port characteristics of the converters. 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. A two-port small signal minimal model building module is used to build a two-port small signal minimal model according to 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 Y through impedance measurement method bus All elements of the busbar admittance matrix are constructed; The stability criterion acquisition module analyzes the determinant of the busbar admittance matrix det(Y bus ) characteristics, we obtain the necessary and sufficient conditions for the stability of multi-bus DC systems: the determinant of the bus admittance matrix det(Y bus ) has zero right half plane zero points; The evaluation module uses the determinant of the busbar admittance matrix det(Y bus ) of the Bode diagram, 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 det(Y bus ) is zero, which is a necessary and sufficient condition for judging the stability of the multi-bus DC system.

10. A computer-readable storage medium, characterized in that: When the computer-readable instructions are executed by one or more processors, the one or more processors execute the steps of the method for determining stability of a multi-bus type DC system based on a bus admittance matrix as described in any one of claims 1 to 8.

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