Local oscillation identification method and device based on bus admittance matrix determinant

Abstract

The invention discloses a bus admittance matrix determinant-based local oscillation identification method and device, and the method and device are suitable for a multi-bus DC power distribution system, and the multi-bus DC power distribution system comprises r DC buses and r-1 interconnection converters. It is assumed that all bus nodes are stable before accessing the system, all interconnection converters operate independently and stably, and the judgment condition of system local oscillation is that a transformation matrix determinant of a bus admittance matrix does not have a right half plane zero point; the same right half plane zero point exists in the admittance matrix determinant of the subsystem and the matrix determinant of the whole system. The oscillation region can be judged by transforming the amplitude and phase change of the determinant sum of the matrix. All elements in the admittance matrix can be obtained through measurement, and the method can be used for oscillation type identification and oscillation area positioning of the black box system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronics, and particularly relates to a local oscillation identification method and device based on a bus admittance matrix determinant. BACKGROUND

[0002] With a large amount of new energy connected to the power grid system, a DC distribution system with high flexibility, high efficiency and greater transmission energy has attracted widespread attention. However, the traditional single-bus DC distribution system cannot meet the power supply demand of various types of DC loads, and the DC distribution system presents a multi-bus characteristic. However, the series and parallel connection of a large number of power electronic converters in the multi-bus DC distribution system leads to weak damping characteristics of the DC distribution system, and the strong coupling between the power electronic converters leads to oscillation problems in the bus of the system.

[0003] With the diversified development of new energy and DC loads, a DC distribution power system (DPS) is widely used in new energy power grids, data centers, ship power systems and electric vehicle charging networks. Such a system usually adopts a multi-bus structure, and each bus is connected to each other through multiple power electronic converters, thereby realizing the control of energy flow in multiple voltage levels. Due to the parallel operation of a large number of power electronic devices in the system and the complex control coupling relationship, the stability problem of the system is increasingly prominent, especially the small signal oscillation and the mutual coupling oscillation between the multi-buses.

[0004] The existing stability analysis methods are mainly based on impedance ratio criterion or admittance matrix method. Among them, the impedance ratio method establishes the equivalent circuit of the source side and the load side impedance, and uses the Nyquist criterion to judge whether the system is stable. This method has good applicability in single-bus systems, but in multi-bus systems, due to the sharp increase in the order of transfer function, the calculation complexity is significantly improved, and the premise that each subsystem has no right half plane pole is difficult to meet, resulting in inaccurate criterion results.

[0005] To overcome the limitations of the impedance ratio method, some researches have proposed improved criteria based on node admittance matrix or bus admittance matrix, which realize the evaluation of the overall stability of the system by calculating the determinant or eigenvalue of the system admittance matrix. However, this kind of method can only judge whether the system is stable as a whole, and cannot distinguish the difference between local oscillation and global oscillation. In the multi-bus DC system, the control strategy and parameter difference of the power electronic converters of different buses may lead to oscillation in only part of the buses, while other buses remain stable, i.e. local oscillation phenomenon. The existing criterion cannot accurately locate the oscillation source bus, and cannot distinguish the type of oscillation.

[0006] In addition, the existing Nyquist or Bode diagram analysis method is easily affected by the phase shift caused by the integral element in the multi-bus system, resulting in misjudgment. With the increase of the scale and complexity of the DC power distribution system, there is an urgent need for a multi-bus type DC power distribution system oscillation identification method capable of distinguishing global and local oscillations. SUMMARY

[0007] The purpose of the present application is to provide a local oscillation identification method and device based on the determinant of the bus admittance matrix, which is used to solve the above technical problems.

[0008] The present application solves the above technical problems by using the following technical solutions:

[0009] The present application provides a local oscillation identification method based on the determinant of the bus admittance matrix, wherein the multi-bus type DC power distribution system includes r DC buses and r-1 interconnected converters, and the method comprises:

[0010] An equivalent admittance model of a single bus and a small signal model of the i-th interconnected converter are established; the models are established on the premise that the equivalent output impedance of the single bus terminal has no right half plane pole and all interconnected converters are stable alone;

[0011] The small signal model of the i-th interconnected converter includes , , and , wherein , , and are the closed-loop transfer functions of the i-th interconnected converter from , to , to and to , wherein and represent the bus voltage, and represent the input current and output current of the i-th interconnected converter;

[0012] Based on the small signal model of the i-th interconnected converter, the bus admittance matrix model of the multi-bus type DC power distribution system is obtained ;

[0013] Based on the bus admittance matrix model , the sufficient and necessary condition for the stability of the entire multi-bus type DC power distribution is that the determinant of the bus admittance matrix has no right half plane zero, and the stability of the DC power distribution system is evaluated through the Bode diagram amplitude and phase information of the bus admittance matrix model;

[0014] The multi-bus type DC power distribution system is divided into two subsystem areas, and the bus admittance matrix model is divided into four matrices 、 、 and ; wherein, the and respectively represent the bus admittance matrix of the subsystem area 1 and area 2, the and represent mutual admittance matrix;

[0015] According to the mathematical equivalent relationship of the bus admittance matrix model and the bus admittance matrix of the subsystem area 1 and area 2, the condition of local oscillation determination is obtained; the condition of local oscillation determination is that the determinant has no right half plane zero point.

[0016] In an embodiment, the equivalent admittance model of the single bus and the closed-loop transfer function of the ith interconnected converter 、 、 and are obtained by the method of impedance measurement.

[0017] The precondition of impedance measurement is that the single bus is stable before being connected to the system, and all interconnected converters are stably operated alone, which satisfies the following conditions:

[0018] ,

[0019] ,

[0020] In the formula, and respectively represent the number of right half plane zero points and poles of the transfer function; 、 、 represent the equivalent admittance of the single bus before being connected to the system.

[0021] In an embodiment, based on the small signal model of the interconnected converter, the expression of the bus admittance matrix of the multi-bus type DC power distribution system is obtained as follows:

[0022] ,

[0023] In the formula, is the input admittance transfer function of the first interconnected converter, 、 the output admittance transfer function of the 1st, r-1th interconnected converter, respectively, , the closed-loop transfer function of the 1st, r-1th interconnected converter from to , respectively, , the closed-loop transfer function of the 1st, r-1th interconnected converter from to .

[0024] In an embodiment, the sufficient and necessary condition for the stability of the entire multi-bus type DC power distribution system is that the determinant of the bus admittance matrix has no right half plane zero, the right half plane zero of which is obtained through the amplitude frequency and phase frequency information of :

[0025] ,

[0026] wherein, and represent the frequency points before and after the resonance occurs; represents the change of the amplitude slope of the determinant of the bus admittance matrix before and after the resonance occurs; represents the phase change of the determinant of the bus admittance matrix before and after the resonance occurs; and represent the number of right half plane zeros and poles of , respectively;

[0027] the right half plane pole of is obtained through the amplitude frequency and phase frequency information of the equivalent admittance model of a single bus

[0028] ,

[0029] wherein, represents the number of right half plane poles of ; represents the change of the amplitude slope of the equivalent admittance of a single bus before and after the resonance occurs; represents the phase change of the equivalent admittance of a single bus before and after the resonance occurs.

[0030] In an embodiment, the bus admittance matrix of the subsystem area 1 and the bus admittance matrix of the area 2 have the following relationship with the bus admittance matrix model :

[0031] ,

[0032] wherein and denote the mutual admittance matrix.

[0033] In one embodiment, the determinant The right half plane zero is denoted as:

[0034] ,

[0035] wherein denotes the amplitude and phase variation at the oscillation frequency ; denotes the change of amplitude slope before and after the resonance occurs; denotes the phase variation before and after the resonance occurs.

[0036] When is 0, it indicates that the system has a local oscillation;

[0037] When is not 0, the system has a global oscillation.

[0038] In one embodiment, the method further comprises: judging the range of local oscillation by transforming the determinant and the amplitude and phase variation at the oscillation frequency.

[0039] In one embodiment, the method of judging the range of local oscillation by transforming the determinant and the amplitude and phase information at the oscillation frequency, specifically:

[0040] ,

[0041] ,

[0042] wherein and denote and d the amplitude and phase variation at the oscillation frequency ; and denote and the change of amplitude slope before and after the resonance occurs; and denote and the phase variation before and after the resonance occurs.

[0043] When when k is 0, there is no right half plane zero at the oscillation frequency indicating that the oscillation range is subsystem region 1;

[0044] when k is 0, there is no right half plane zero at the oscillation frequency indicating that the oscillation range is subsystem region 2.

[0045] The application also provides a local oscillation identification device for a multi-bus type DC power distribution system, the multi-bus type DC power distribution system comprising r DC buses and r-1 interconnected converters, the device comprising:

[0046] an equivalent admittance and small signal model construction module, configured to establish an equivalent admittance model of a single bus and a small signal model of an i-th interconnected converter; the model is established on the premise that the equivalent output impedance of a single bus terminal has no right half plane pole and all interconnected converters are stable independently;

[0047] the small signal model of the i-th interconnected converter comprises , , and , wherein , , and are closed-loop transfer functions of the i-th interconnected converter from to , to , to and to , wherein and represent bus voltages, and represent input and output currents of the i-th interconnected converter;

[0048] a bus admittance matrix model module, configured to derive a bus admittance matrix model of the multi-bus type DC power distribution system based on the small signal model of the i-th interconnected converter ;

[0049] a multi-bus type DC power distribution stability determination module, configured to derive a sufficient and necessary condition for the stability of the entire multi-bus type DC power distribution based on the bus admittance matrix model , that is, the bus admittance matrix has no right half plane zero, and evaluate the stability of the DC power distribution system through the amplitude and phase information of the Bode plot of the bus admittance matrix model;

[0050] ​​The regional division module is configured to divide the multi-bus type DC power distribution system into two subsystem regions and divide the bus admittance matrix model into four matrices 、 、 and ; wherein, the and respectively represent bus admittance matrices of the subsystem region 1 and the region 2, and the and represent mutual admittance matrices

[0051] The oscillation identification module is configured to obtain a condition for local area oscillation determination according to the mathematical equivalent relationship between the bus admittance matrix model and the bus admittance matrices of the subsystem region 1 and the region 2. The condition for the local area oscillation determination is that the determinant

[0052] In an embodiment, the device further comprises: a module for judging the range of the local area oscillation by the amplitude and phase changes of the determinant and of the transformation matrix at the oscillation frequency.

[0053] Advantages of the application:

[0054] (1) The application is suitable for the cascade type or parallel type multi-bus DC system, and for the system instability, the amplitude and phase change trend in the Bode diagram is used to judge the local area oscillation, without requiring detailed internal parameter information, and the application is suitable for black box system.

[0055] (2) For the local area oscillation problem, the amplitude and phase frequency change trend of the bus admittance matrix transformation matrix can be used to directly judge the oscillation range.

[0056] (3) All elements in the matrix can be obtained by impedance measurement, without requiring internal parameter information of the multi-bus system, and the application is convenient for engineering practice. BRIEF DESCRIPTION OF DRAWINGS

[0057] The accompanying drawings, which are part of the present application, serve to further understand the present application, and the schematic embodiments of the present application and the descriptions thereof serve to explain the present application, but do not constitute improper limitation on the present application. Obviously, the accompanying drawings in the following description are only some embodiments, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the drawings.

[0058] Figure 1 It is a topological structure diagram of the multi-bus type DC system;

[0059] Figure 2An embodiment of the present application provides a local oscillation identification method based on bus admittance matrix determinant flow chart;

[0060] Figure 3 For multi-bus type DC system two-port small signal model diagram;

[0061] Figure 4 For the three-bus DC system application example simulation topology provided in an embodiment of the present application;

[0062] Figure 5 For the Bode diagram provided in an embodiment of the present application, wherein Figure 5 In (a), when and , , , and Bode diagram, Figure 5 In (b), when and , and Bode diagram, Figure 5 In (c), when and , and Bode diagram;

[0063] Figure 6 For the experimental waveform diagram provided in an embodiment of the present application, wherein Figure 6 In (a), when and , , and Waveform diagram, Figure 6 In (b), when and , , , and Waveform diagram, Figure 6 In (c), when and , , , and Waveform diagram, Figure 6 (d) is and , , , and Waveform diagram.

[0064] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0065] To enhance understanding of the present invention, the technical solution of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The following embodiments are explanations of the present invention, but the present invention is not limited to the following embodiments.

[0066] 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.

[0067] The topology of a multi-bus DC system is as follows: Figure 1 As shown, a multi-bus DC system comprises r DC buses and r-1 interconnecting converters. Multiple GVS (Generalized Voltage Source) and GCS (Generalized Current Source) are connected in parallel on each DC bus. Figure 1 The middle part indicates that each DC bus is connected in parallel. GVS and One GCS.

[0068] Reference Figure 2 As shown in the figure, an embodiment of the present invention illustrates a method for identifying local oscillations based on the determinant of the bus admittance matrix. The method includes the following steps:

[0069] Step S100: Establish the equivalent admittance model of a single bus and the small-signal model of the i-th interconnect converter.

[0070] The equivalent admittance model of a single bus and the small-signal model of the i-th interconnect converter are established under the premise that the equivalent output impedance of a single bus terminal has no right half-plane poles and all interconnect converters are individually stable.

[0071] Reference Figure 3 As shown in the figure Let be the Norton equivalent current of the 1st, 2nd, ..., rth buses; System response quantity; The input current disturbance of the first, second, ..., r buses. and Let x be the input / output current disturbance of the x-th interconnect converter. .

[0072] Based on the port characteristics of GVS and GCS, an equivalent admittance model for a single bus is established. and the small-signal model of the i-th interconnect converter , , and The equivalent output impedance of the single bus terminal has no right half plane pole and all the interconnecting converters are individually stable.

[0073] , , and are the closed loop transfer functions of the ithinterconnecting converter from to , to , to and to respectively. That is, the small signal model of the ithinterconnecting converter is represented by the closed loop transfer functions of the ithinterconnecting converter from bus voltage to interconnecting converter input current , bus voltage to interconnecting converter input current , bus voltage to ithinterconnecting converter output current and bus voltage to ithinterconnecting converter output current .

[0074] Further, the equivalent admittance model of the single bus and the closed loop transfer functions of the ithinterconnecting converter , , and are obtained by the method of impedance measurement. The preconditions of impedance measurement are that the single bus is stable before it is connected to the multi-bus DC system and all the interconnecting converters are individually stable and satisfy the following conditions:

[0075] (1)

[0076] (2)

[0077] where and are the number of right half plane zeros and poles of the transfer function respectively, , , is the equivalent admittance of the single bus before it is connected to the system; , , and are the small signal closed loop transfer functions of the ithinterconnecting converter.

[0078] Step S200: Based on the small signal model of the ith interconnected converter, the bus admittance matrix model of the multi-bus DC power distribution system is derived .

[0079] Further, the expression of the bus admittance matrix is:

[0080] (3)

[0081] In the formula, is the input admittance transfer function of the 1st interconnected converter, , are the output admittance transfer functions of the 1st and r-1th interconnected converters respectively, , are the closed-loop transfer functions of the 1st and r-1th interconnected converters from to , , are the closed-loop transfer functions of the 1st and r-1th interconnected converters from to .

[0082] Step S300: Based on the bus admittance matrix model , the sufficient and necessary condition for the stability of the entire multi-bus DC power distribution system is that the bus admittance matrix determinant has no right half plane zero, and the stability of the DC power distribution system is evaluated through the amplitude and phase information of the Bode diagram of the bus admittance matrix model.

[0083] Further, the sufficient and necessary condition for the stability of the entire DC power distribution system is that the bus admittance matrix determinant has no right half plane zero, the right half plane zero of can be directly obtained through the amplitude and phase information of :

[0084] (4)

[0085] In the formula, and represent the frequency points before and after the resonance occurs; represents the change of the amplitude slope of the bus admittance matrix determinant before and after the resonance occurs; represents the phase change of the bus admittance matrix determinant before and after the resonance occurs; and respectively represent the number of right half plane zeros and poles of ;

[0086] The equivalent admittance model of the right half plane pole of a single bus The amplitude and phase information of

[0087] (5)

[0088] In the formula, represents The number of right half plane poles of represents the change of amplitude slope of the equivalent admittance of a single bus before and after the resonance occurs. represents the phase change of the equivalent admittance of a single bus before and after the resonance occurs.

[0089] Step S400: Divide the multi-bus type DC power distribution system into two subsystem areas, and divide the bus admittance matrix model into four matrices 、 、 and .

[0090] Specifically, the multi-bus type DC power distribution system is divided into two subsystem areas, and the bus admittance matrix model is divided into 、 、 and four matrices, and represent the bus admittance matrix of the subsystem area 1 and area 2 respectively, and represent the mutual admittance matrix.

[0091] Further, the bus admittance matrix of the subsystem area 1 and the bus admittance matrix of the area 2 The mutual relationship of the bus admittance matrix model is:

[0092] (6)

[0093] In the formula, and represent the mutual admittance matrix.

[0094] Step S500: According to the mathematical equivalent relationship of the bus admittance matrix model and the bus admittance matrix of the subsystem area 1 and area 2, the condition for local oscillation determination is obtained.

[0095] The condition for local oscillation determination is that the determinant has no right half plane zero point.

[0096] Further, the right half plane zero point of the determinant is expressed as:

[0097] (7)

[0098] wherein, represents the amplitude and phase variation at the oscillation frequency ; represents the variation of amplitude slope before and after the resonance occurs; represents the phase variation before and after the resonance occurs;

[0099] The specific determination method is: when is 0, it indicates that the system occurs local oscillation, and when is not 0, it indicates that the system occurs global oscillation.

[0100] In a preferred embodiment, after identifying that the system occurs oscillation, further comprising: judging the range of local oscillation by the amplitude and phase variation of the transformation matrix determinant and at the oscillation frequency.

[0101] The specific method is: by the amplitude and phase variation of the transformation matrix determinant

[0102] (8)

[0103] (9)

[0104] wherein, and represent and the amplitude and phase variation at the oscillation frequency ; and represent and the variation of amplitude slope before and after the resonance occurs; and represent and the phase variation before and after the resonance occurs.

[0105] When is 0, there is no right half plane zero point at the oscillation frequency , which indicates that the oscillation range is the subsystem region 1;

[0106] When is 0, there is no right half plane zero point at the oscillation frequency , which indicates that the oscillation range is the subsystem region 2. ​

[0107] The following takes a three-bus type DC system composed of six Buck converters as an example, as shown in Figure 4 . , , and are the switch tube, diode, inductor and capacitor of the Buck converter respectively; and are load resistances; and are the input voltage of converter 1, the input voltage of converter 5, bus voltage 1, bus voltage 2, bus voltage 3, the output voltage of converter 3, the output voltage of converter 6, the output current of converter 2, the output current of converter 3, the output current of converter 4 and the output current of converter 6 respectively. and are the output impedance of converter 1 and converter 5; and are the input impedance of converter 3 and converter 6.

[0108] The application effect of the technical scheme of the present application is verified in combination with experimental results. The main parameters of the experimental system are shown in Table 1.

[0109] Table 1 Main parameters of experiment

[0110]

[0111] Figure 5 Fig. (a) gives the Bode diagram of and when , and , it can be seen from the figure that the amplitude and phase change trend of , and are consistent, so , indicating .

[0112] Figure 5 Fig. (b) gives the Bode diagram of and when and , it can be seen from the figure that the phase frequency curve of exists a anti-resonance point at 580Hz, and the phase drops by 180°, indicating there are two right half plane (right half plane, RHP) zero points, and the whole system is unstable. The amplitude and phase change are consistent, and there is no right half plane zero or pole at 580Hz, so the system has local oscillation problem. Figure 5 In (c) of the drawings and When and The Bode diagram can be seen from the figure, The amplitude and phase change are consistent, and there is no right half plane zero or pole, which means that the subsystem 1 is unstable. There are two right half plane zeros at the oscillation frequency 580Hz, which means that the subsystem 2 is stable.

[0113] Figure 6 In (a) of the drawings and When , and The waveform diagram can be seen from the figure, the system is obviously unstable, and and There is oscillation in (c), while There is no oscillation in (d), which indicates that there is a local oscillation problem in the system, and the subsystem 1 is unstable, and the subsystem 2 is stable, and the oscillation frequency is 580Hz, which is consistent with Figure 5 The analysis result. Figure 6 In (b) of the drawings and When , , and The waveform diagram can be seen from the figure, and the subsystem 1 is unstable, which is consistent with Figure 5 The result in (c) of the drawings. Figure 6 In (c) and (d) of the drawings and When , , , , and The waveform diagram can be seen from the figure, , and are stable, and the subsystem 2 is stable, which is consistent with Figure 5 The result in (c) of the drawings.

[0114] In summary, the experiment verifies that the local area oscillation identification and positioning method of the multi-bus type DC system based on the bus admittance matrix determinant of the application, the local oscillation can be judged by the Bode diagram of the bus admittance matrix determinant Whether there is a right half plane zero at the oscillation frequency.

[0115] The following is an embodiment of the local oscillation identification device based on the bus admittance matrix determinant of the present invention, which can be used to execute the local oscillation identification method based on the bus admittance matrix determinant of the present invention.

[0116] This invention discloses a local oscillation identification device for a multi-bus DC distribution system. The multi-bus DC distribution system includes r DC buses and r-1 interconnecting converters. The device includes:

[0117] The equivalent admittance and small-signal model construction module is used to establish the equivalent admittance model of a single bus and the small-signal model of the i-th interconnect converter. The model is established under the premise that the equivalent output impedance of a single bus terminal has no right half-plane poles and all interconnect converters are individually stable.

[0118] The small-signal model of the i-th interconnect converter includes , , and The , , and The i-th interconnect converter is from arrive , arrive , arrive and arrive The closed-loop transfer function, where and Indicates bus voltage. and This represents the input and output currents of the i-th interconnect converter;

[0119] The bus admittance matrix model module is used to derive the bus admittance matrix model of a multi-bus DC distribution system based on the small-signal model of the i-th interconnected converter. ;

[0120] Multi-bus DC power distribution stability determination module, used for bus admittance matrix model The necessary and sufficient condition for the stability of the entire multi-bus DC power distribution system is the determinant of the bus admittance matrix. Without right-half-plane zeros, the stability of the DC power distribution system is evaluated using the Bode plot magnitude and phase information of the bus admittance matrix model;

[0121] The region division module is used to divide a multi-bus DC power distribution system into two subsystem regions and to divide the bus admittance matrix model into four matrices. , , and ; wherein, the and respectively represent the bus admittance matrix of subsystem area 1 and area 2, the and represent the mutual admittance matrix;

[0122] an oscillation identification module, configured to derive a condition of local area oscillation determination according to the mathematical equivalent relationship between the bus admittance matrix model and the bus admittance matrix of subsystem area 1 and area 2; the condition of local area oscillation determination is that the determinant has no right half plane zero point.

[0123] In a preferred embodiment, the device further comprises a positioning module, configured to determine the range of local area oscillation by transforming the determinant and of the amplitude and phase variation at the oscillation frequency.

[0124] It should be noted that the multi-bus type DC power distribution system local area oscillation identification device provided in the above embodiments is only used for example to divide the above functional modules when the multi-bus type DC power distribution system local area oscillation identification method is executed, and in actual application, the above functions can be completed by different functional modules according to needs, that is, the internal structure of the device is divided into different functional modules to complete all or part of the above described functions. In addition, the multi-bus type DC power distribution system local area oscillation identification device and the multi-bus type DC power distribution system local area oscillation identification method provided in the above embodiments belong to the same concept, and the implementation process is described in detail in the multi-bus type DC power distribution system local area oscillation identification method, which will not be repeated here.

[0125] The above only describes preferred embodiments of the present application and does not limit the present application in any form. Although the present application has been disclosed as above, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above-mentioned technical content without departing from the scope of the technical solution of the present application, and any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present application still belong to the scope of the present application.

Claims

1. A method and device for identifying local oscillation based on bus admittance matrix determinant, characterized in that: The multi-bus type direct current power distribution system contains r direct current buses and r-1 interconnected converters, and the method comprises: establishing an equivalent admittance model of a single bus and a small signal model of the i th interconnected converter; the models are established on the premise of ensuring that the equivalent output impedance of the terminal of the single bus has no right half plane pole and all interconnected converters are stable alone; The ith interconnected converter small signal model comprises , , and , the , , and are closed-loop transfer functions from to , to , to and to of the ith interconnected converter, wherein and represent bus voltages, and represent input and output currents of the ith interconnected converter; Based on the small signal model of the ith interconnected converter, the bus admittance matrix model of the whole multi-bus DC distribution system is derived ; Bus admittance matrix model The sufficient and necessary condition for the stability of the entire multi-bus type DC power distribution is the determinant of the bus admittance matrix Without the right half plane zero point, and through the amplitude and phase information of the Bode diagram of the bus admittance matrix model to evaluate the stability of the DC power distribution system; The multi-bus type DC power distribution system is divided into two subsystem areas, and the bus admittance matrix model is divided into four matrices 、 、 and ; wherein, the and respectively represent the bus admittance matrix of the subsystem area 1 and area 2, and the and represent mutual admittance matrixes; According to the bus admittance matrix model The mathematical equivalent relationship of the bus admittance matrix of the subsystem area 1 and the area 2 is obtained, and the condition of the local oscillation determination is obtained; the condition of the local oscillation determination is that the determinant There is no right half plane zero point.

2. The bus admittance matrix determinant based local oscillation identification method and device according to claim 1, characterized in that: Obtaining an equivalent admittance model of a single busbar by means of impedance measurements and the closed loop transfer function of the ith interlinked converter 、 、 and ; The premise condition of impedance measurement is that the single bus is stable before being connected to the system, and all interconnected converters are stably operated alone, and the following conditions are met: ， ， wherein and denote the number of right half plane zero and pole of the transfer function, respectively; , , denotes the equivalent admittance of the single bus before connecting to the system.

3. The bus admittance matrix determinant-based local oscillation identification method and device according to claim 2, characterized in that: The bus admittance matrix model The expression is: ， wherein G1is the input admittance transfer function of the first interconnection transformer, , G1, Gr-1are the output admittance transfer functions of the first, r-1 interconnection transformer, respectively, , G1, Gr-1are the closed loop transfer functions of the first, r-1 interconnection transformer from to , respectively, , G1, Gr-1are the closed loop transfer functions of the first, r-1 interconnection transformer from to , respectively.

4. The bus admittance matrix determinant-based local oscillation identification method and device according to claim 3, characterized in that: The sufficient and necessary condition of the stability of the whole multi-bus type DC power distribution system is the bus admittance matrix determinant There is no right half-plane zero, The right half-plane zero of the transfer function is obtained by The amplitude and phase information of the transfer function ， In the formula, and indicates the frequency point before and after the resonance occurs; indicates the change in amplitude slope of the determinant of the bus admittance matrix before and after the resonance occurs; indicates the phase change of the determinant of the bus admittance matrix before and after the resonance occurs; and respectively indicate the number of right half-plane zero points and poles of Right half plane pole of the equivalent admittance model of a single bus Magnitude and phase information is obtained: ， In the formula, represents the number of right half plane poles of the transfer function represents the change in the amplitude slope of the single bus equivalent admittance before and after resonance occurs; represents the change in the phase of the single bus equivalent admittance before and after resonance occurs.

5. The bus admittance matrix determinant-based local oscillation identification method and device according to claim 1 or 4, characterized in that: bus admittance matrix of subsystem area 1 bus admittance matrix of area 2 correlation with bus admittance matrix model of ， wherein and denotes the mutual admittance matrix.

6. The bus admittance matrix determinant based local oscillation identification method and device according to claim 5, characterized in that: determinant The right half plane zero is represented as: ， wherein represents the amplitude and phase changes at the oscillation frequency at the oscillation frequency; represents the change in the slope of the amplitude before and after resonance occurs; represents the change in the phase before and after resonance occurs; When is 0, it indicates that the system has local oscillation; When If not 0, it indicates that the system has global oscillation.

7. The bus admittance matrix determinant based method and apparatus for identifying local oscillations as recited in claim 6, characterized in that: The method further comprises: By the determinant of the transformation matrix and The amplitude and phase changes at the oscillation frequency are used to determine the extent of the local oscillation.

8. The bus admittance matrix determinant-based local oscillation identification method and device according to claim 7, characterized in that: The determinant of the transformation matrix And The amplitude and phase information at the oscillation frequency are used to determine the range of the local oscillation. The specific method is: ， ， wherein and denotes and the amplitude-frequency and phase-frequency change at the oscillation frequency ; and denotes and the change in the slope of the amplitude before and after the resonance occurs; and denotes and the phase change before and after the resonance occurs; When is 0, there is no right-half plane zero at the oscillation frequency , indicating that the oscillation range is subsystem region 1; When For 0, there is no right-half plane zero at the oscillation frequency place, indicating that the oscillation range is subsystem region 2.

9. A method and device for identifying local oscillation based on bus admittance matrix determinant, characterized in that: The multi-bus type direct current power distribution system contains r direct current buses and r-1 interconnected converters, and the device comprises: an equivalent admittance and small signal model construction module, configured to establish an equivalent admittance model of a single bus and a small signal model of the i th interconnected converter; the models are established on the premise of ensuring that the equivalent output impedance of the terminal of the single bus has no right half plane pole and all interconnected converters are stable alone; The ith interconnected converter small signal model comprises , , and , wherein , , and are closed-loop transfer functions from to , to , to and to respectively, wherein and denote bus voltages, and denote input and output currents of the ith interconnected converter; a bus admittance matrix model module configured to derive a bus admittance matrix model of the multi-bus DC distribution system based on a small signal model of the ith interconnected converter ; The multi-bus type DC power distribution stability determination module is used for determining the stability of the multi-bus type DC power distribution system based on the bus admittance matrix model , and the sufficient and necessary condition for the stability of the entire multi-bus type DC power distribution system is that the bus admittance matrix determinant has no right half-plane zero point, and the stability of the DC power distribution system is evaluated through the amplitude and phase information of the Bode diagram of the bus admittance matrix model. The regional division module is used for dividing the multi-bus type DC power distribution system into two subsystem regions and dividing the bus admittance matrix model into four matrices 、 、 and ; wherein, the and respectively represent the bus admittance matrix of the subsystem region 1 and region 2, and the and represent the mutual admittance matrix; The oscillation identification module is used to identify the oscillation based on the bus admittance matrix model. Based on the mathematical equivalence relationship between the bus admittance matrices of subsystem regions 1 and 2, the condition for determining local oscillations is derived; the condition for determining local oscillations is: determinant There is no zero point in the right half-plane.

10. The method and device for identifying local oscillation based on bus admittance matrix determinant according to claim 9, characterized in that: The device further comprises: a positioning module for determining the position of the device by means of the determinant of the transformation matrix and the amplitude and phase change at the oscillation frequency to determine the range of the local oscillation.

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