M3C power frequency and low frequency coupling characteristic analysis method and system

Abstract

The invention discloses an M3C power frequency and low frequency coupling characteristic analysis method and system. The method comprises the steps that S1, positive sequence small signal voltage disturbance is injected into the power frequency side and the low frequency side of an M3C; s2, based on the positive sequence small signal voltage disturbance, establishing a frequency domain response model of M3C bridge arm voltage and equivalent module capacitor voltage, and analyzing frequency distribution through Fourier transform; s3, determining small signal frequency components coupled with the power frequency and the low frequency in the bridge arm voltage and the equivalent module capacitor voltage according to the phase sequence relation of the power frequency side control signal and the low frequency side control signal; and S4, offsetting the coupling frequency component through the phase sequence relation of the power frequency side control signal and the low frequency side control signal, so that the coupling frequency component has no influence on the dynamic characteristics of the power frequency side and the low frequency side of the M3C. According to the invention, the dynamic performance and stability of the M3C system can be optimized.

Description

TECHNICAL FIELD

[0001] The present application mainly relates to the technical field of power grid, and particularly relates to a M3C power frequency and low frequency frequency coupling characteristic analysis method and system. BACKGROUND

[0002] M3C (Modular Multilevel Matrix Converter) is a topological structure suitable for medium and high voltage and high power electric energy conversion, which is formed by interconnecting a plurality of sub-modules (SM) in a matrix form, each phase containing a plurality of series-connected sub-modules, and each sub-module being composed of a half-bridge or full-bridge circuit and a capacitor. The input side (high voltage) and the output side (low voltage) both adopt a three-phase structure, and the energy flows bidirectionally through the charging and discharging of the sub-module capacitors, and supports voltage conversion of different frequencies / amplitudes.

[0003] The M3C (Modular Multilevel Matrix Converter) high / low frequency side is connected through the same bridge arm, and the dynamic characteristics of the equivalent module capacitor voltage of the bridge arm and the bridge arm voltage may cause frequency coupling effect on the high / low frequency side, and the ambiguous high / low voltage side coupling characteristics are not conducive to the development of control strategies. SUMMARY

[0004] In view of the technical problems existing in the prior art, the present application provides a M3C power frequency and low frequency frequency coupling characteristic analysis method and system for optimizing the dynamic performance and stability of the M3C system.

[0005] To solve the above technical problems, the technical solution provided by the present application is as follows:

[0006] A M3C power frequency and low frequency frequency coupling characteristic analysis method, comprising the following steps:

[0007] Injecting a positive sequence small signal voltage disturbance on the power frequency side and the low frequency side of the M3C respectively;

[0008] Based on the positive sequence small signal voltage disturbance, a frequency domain response model of the bridge arm voltage and the equivalent module capacitor voltage of the M3C is established, and the frequency distribution is analyzed by Fourier transform;

[0009] According to the phase sequence relationship of the control signals on the power frequency side and the low frequency side, the small signal frequency components in the bridge arm voltage and the equivalent module capacitor voltage which are coupled with the power frequency and the low frequency are determined;

[0010] The coupled frequency components are offset by the phase sequence relationship of the control signals on the power frequency side and the low frequency side, so that the coupled frequency components have no influence on the dynamic characteristics of the M3C power frequency side and the low frequency side.

[0011] Preferably, based on the positive sequence small signal voltage disturbance, a frequency domain response model of the M3C bridge arm voltage and the equivalent module capacitor voltage is established, and the specific process of analyzing the frequency distribution thereof through Fourier transform is as follows:

[0012] According to the M3C average equivalent circuit, the bridge arm voltage of the M3C is equivalent to:

[0013] u yx = m yx v cyx (1)

[0014] In the formula, x is a, b, and c, which correspond to the a, b, and c phases of the low-frequency side of the M3C; y is u, v, and w, which correspond to the u, v, and w phases of the power frequency side of the M3C; u yx is the voltage of the bridge arm yx; v cyx is the equivalent module capacitor voltage of the bridge arm yx; m yx is the total control signal of the bridge arm yx;

[0015] The overall control of the M3C is composed of the control of the power / low-frequency sides, and the control signal of the M3C is divided into the power frequency side control signal and the low frequency side control signal; formula (1) is further rewritten as:

[0016]

[0017] In the formula, m yxh is the power frequency side y phase control signal; m yxl is the low frequency side x phase control signal;

[0018] The variables in formula (2) are described in the form of vectors by performing Fourier transform on the equivalent module capacitor voltage of the M3C and the power / low-frequency side control signal, and the expression of the M3C bridge arm voltage u yx in the frequency domain is written as:

[0019]

[0020] In the formula, the frequency distribution of the power frequency side control signal m yxh contains ±f1, the frequency distribution of the bridge arm equivalent module capacitor voltage v cyx contains ±2f1, ±(f1+f2), ±2f2, and ±(f1-f2), and the frequency distribution of the low frequency side control signal m yxl contains ±f2.

[0021] Preferably, the phase sequence relationship of the M3C power / low-frequency control signals m yxh and m yxl in each sub-converter is:

[0022] For the M3C power / low-frequency control signal m yxh, the phase sequence relationship in the a, b and c phase sub-converter is positive sequence, and the phase sequence relationship in the u, v and w phase sub-converter is zero sequence;

[0023] For M3C, the high-frequency control signal m yxl , the phase sequence relationship in the a, b and c phase sub-converter is zero sequence, and the phase sequence relationship in the u, v and w phase sub-converter is positive sequence.

[0024] Preferably, the cancellation mechanism of the phase sequence relationship is specifically: when a disturbance is injected on the high-frequency side, the positive sequence and negative sequence components coupled with the high-frequency frequency in the equivalent module capacitor voltage are cancelled in the view of the high-frequency sub-converter; when a disturbance is injected on the low-frequency side, the positive sequence and negative sequence components coupled with the low-frequency frequency in the bridge arm voltage are cancelled in the view of the low-frequency sub-converter.

[0025] Preferably, the influence of the 3 times high-frequency / low-frequency frequency components on the stability of the system is suppressed by increasing the cascade sub-module capacitor or setting an angle connection transformer on the high / low-frequency side.

[0026] Preferably, it further includes verifying the effectiveness of the cancellation mechanism, including harmonic spectrum analysis of the bridge arm voltage and the equivalent module capacitor voltage in the simulation model.

[0027] Preferably, the specific process of verifying the effectiveness of the cancellation mechanism is: building an M3C model in a simulation platform, analyzing the frequency spectrum of the bridge arm voltage and the equivalent module capacitor voltage through fast Fourier transform, and verifying that the amplitude of the coupled frequency components is lower than a preset threshold.

[0028] The application further discloses a computer program product, including a computer program, which executes the steps of the method when run by a processor.

[0029] The application further discloses a computer readable storage medium, which stores a computer program, and the computer program executes the steps of the method when run by a processor.

[0030] The application further discloses an M3C high-frequency and low-frequency frequency coupling characteristic analysis system, including a memory and a processor connected with each other, the memory stores a computer program, and the computer program executes the steps of the method when run by the processor.

[0031] Compared with the prior art, the application has the following advantages:

[0032] The application is directed to an innovative analysis method for the frequency coupling characteristics of a modular multilevel matrix converter (M3C) at power frequency and low frequency, which reveals the generation path and cancellation mechanism of the coupled frequency components by theoretical modeling, frequency domain analysis and simulation verification, significantly optimizing the dynamic performance and stability of the M3C system; by injecting positive sequence small signal voltage disturbance on the power frequency side and the low frequency side respectively, combining Fourier transform and frequency domain convolution analysis, the distribution law of the coupled frequency components in the bridge arm voltage and the equivalent module capacitor voltage is determined. The coupled frequency components are effectively cancelled in the sub-converter due to the phase sequence asymmetry of the control signals on the power frequency side and the low frequency side (positive sequence / zero sequence complementary). By increasing the cascade sub-module capacitor or configuring an angle transformer on the power / low frequency side, the current generated by the 3 times power / low frequency frequency components is suppressed to avoid system oscillation or equipment overheating problems.

[0033] The M3C power / low frequency frequency coupling characteristic analysis method based on small signal frequency convolution of the application analyzes whether there is a frequency coupling effect on the power / low frequency side of the M3C, determines the influence of the M3C bridge arm voltage and the equivalent module capacitor voltage on the power / low frequency side dynamic characteristics, solves the dynamic characteristic ambiguity problem caused by the multi-frequency coupling of the M3C through frequency domain modeling and phase sequence cancellation mechanism, provides an effective technical path for harmonic suppression, stability improvement and control strategy optimization of complex converter systems, and is suitable for new energy grid connection, flexible power transmission and other high-performance power electronic application scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 It is an M3C bridge arm voltage harmonic convolution diagram in the application.

[0035] Figure 2 It is an M3C equivalent module capacitor voltage small signal convolution diagram in the application.

[0036] Figure 3 It is an M3C bridge arm voltage small signal convolution diagram in the application.

[0037] Figure 4 It is a u-phase sub-converter bridge arm voltage spectrum diagram in the M3C in the application.

[0038] Figure 5 It is a u-phase sub-converter bridge arm voltage spectrum diagram in the M3C in the application.

[0039] Figure 6 It is a u-phase equivalent module capacitor voltage spectrum diagram in the M3C in the application.

[0040] Figure 7 It is a u-phase bridge arm voltage spectrum diagram in the M3C in the application.

[0041] Figure 8M3C average equivalent circuit diagram in the application.

[0042] Figure 9 Flowchart of the analysis method in the application. DETAILED DESCRIPTION

[0043] The application will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0044] As shown in the drawings, Figure 9 the M3C power frequency and low frequency frequency coupling characteristic analysis method provided by the embodiments of the application comprises the following steps:

[0045] Injecting positive sequence small signal voltage disturbance on the power frequency side and the low frequency side of the M3C;

[0046] Based on the positive sequence small signal voltage disturbance, establishing a frequency domain response model of the bridge arm voltage and the equivalent module capacitor voltage of the M3C, and analyzing the frequency distribution thereof through Fourier transform;

[0047] According to the phase sequence relationship of the control signals on the power frequency side and the low frequency side, determining the small signal frequency components in the bridge arm voltage and the equivalent module capacitor voltage that are coupled with the power frequency and the low frequency;

[0048] Through the phase sequence relationship of the control signals on the power frequency side and the low frequency side, canceling the coupled frequency components, so that the coupled frequency components have no influence on the dynamic characteristics of the power frequency side and the low frequency side of the M3C;

[0049] Verifying the effectiveness of the cancellation mechanism, including harmonic spectrum analysis of the bridge arm voltage and the equivalent module capacitor voltage in the simulation model.

[0050] In order to better understand the above technical solutions, the above technical solutions will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0051] As shown in the drawings, Figure 8 the M3C average equivalent circuit, Figure 8 v cua , v cva , v cwa is the total control signal of the bridge arm u a , v a , w a The sum of the cascade module capacitor voltages; m ua , m va , m wa is the total control signal of the bridge arm u a , v a , w a The equivalent module capacitor of the cascade module is C, and C=C a , v a , w a m ​ / N.

[0052] From the average value model, the bridge arm voltage of M3C can be equivalent to:

[0053] u yx = m yx v cyx (1)

[0054] where x is a, b, c corresponding to a, b, c phase of M3C low frequency side; y is u, v, w corresponding to u, v, w phase of M3C power frequency side; u yx is the voltage of bridge arm yx; v cyx is the equivalent module capacitor voltage of bridge arm yx; m yx is the total control signal of bridge arm yx.

[0055] The overall control of M3C is composed of the control of power / low frequency side respectively, and the control signal of M3C can be divided into power frequency side control signal and low frequency side control signal.

[0056] Formula (1) can be further written as:

[0057]

[0058] where m yxh is the power frequency side y phase control signal; m yxl is the low frequency side x phase control signal.

[0059] By Fourier transform on the equivalent module capacitor voltage of M3C, power / low frequency side control signal, each variable in formula (2) is described in the form of vector, and the expression of M3C bridge arm voltage u yx in frequency domain can be written as:

[0060]

[0061] where the frequency distribution of power frequency side control signal m yxh contains ±f1, the frequency distribution of bridge arm equivalent module capacitor voltage v cyx contains ±2f1, ±(f1+f2), ±2f2, ±(f1-f2), and the frequency distribution of low frequency side control signal m yxl contains ±f2.

[0062] The frequency convolution process of power / low frequency side control signal m yxh , m yxl and bridge arm equivalent module capacitor voltage v cyx and the frequency distribution of bridge arm voltage u yx are shown in Figure 1 .

[0063] M3C power / low frequency control signal myxh 、m yxl The phase sequence relationship in each sub-converter is shown in Table 1.

[0064] Table 1 Phase sequence relationship of M3C industrial / low frequency control signals

[0065]

[0066] Combine Figure 1 From Table 1, we can get the M3C bridge arm voltage u yx The harmonic frequency distribution and phase sequence relationship in each sub-converter are shown in Table 2.

[0067] Table 2 M3C bridge arm voltage harmonic components and phase sequence relationship

[0068]

[0069] Therefore, it can be seen from Table 2 that the M3C bridge arm voltage u yx There are zero-sequence components with frequencies of 3f1, f2, and 3f2 in the a, b, and c phase sub-converters. The frequency components f1, 2f1+f2, f1+2f2, f1-2f2, and 2f1-f2 will be offset due to the phase sequence relationship; the bridge arm voltage u yx There are zero-sequence components with frequencies of 3f1, f1, and 3f2 in the u, v, and w phase sub-converters, and the frequency components f2, 2f1+f2, f1+2f2, f1-2f2, and 2f1-f2 will be offset due to the phase sequence relationship.

[0070] M3C bridge arm voltage u yx The current generated by the three times power / low frequency component flowing into the power / low frequency grid will cause stability problems in the power / low frequency system.

[0071] To this end, the current generated by the three-times-power / low-frequency components can be suppressed by increasing the capacitance of the cascaded submodules and installing delta transformers on the power / low-frequency sides. Therefore, when separately modeling the impedance of the M3C power / low-frequency sides, the impact of the three-times-power / low-frequency components on the M3C's dynamic characteristics can be ignored, and the M3C power / low-frequency sides can still be considered decoupled.

[0072] By injecting small signal voltage disturbance into the power frequency side, the coupling characteristics of the power and low frequency sides under small signal disturbance are analyzed.

[0073] From the instantaneous power balance of the AC and DC sides of the equivalent module, it can be seen that the relationship between the AC and DC side electrical components of the M3C equivalent module is:

[0074]

[0075] In the formula, x is a, b, c, which corresponds to a, b, c phase of M3C low frequency side; y is u, v, w, which corresponds to u, v, w phase of M3C power frequency side; i yx is the bridge arm current of the bridge arm yx.

[0076] The left side of the formula (4) is the expression of the instantaneous power of the DC side of the equivalent module, and the right side is the instantaneous expression formula of the AC side power of the equivalent module. Further simplifying the formula (4) can obtain:

[0077]

[0078] The overall control of M3C is composed of the control of the power / low frequency side, and the control signal of M3C can be divided into the power frequency side control signal and the low frequency side control signal; at the same time, the bridge arm current of M3C is composed of the power frequency component and the low frequency component. The formula (5) can be further written as:

[0079]

[0080] Wherein, i yxh is the power frequency component of the steady-state current of the bridge arm yx; i yxl is the low frequency component of the steady-state current of the bridge arm yx.

[0081] The variables in the formula (6) are described in the form of vectors by Fourier transform of the equivalent module capacitor voltage, power / low frequency side control signal and bridge arm current. The expression of the relationship between the AC and DC side electrical components of the M3C equivalent module in the frequency domain is:

[0082]

[0083] In the formula,

[0084] The vector m yxh , i yxh The frequencies corresponding to the elements from top to bottom are-3f1, -2f1, -f1, 0, f1, 2f1, 3f1, and f1 is the power frequency; the vector m yxl , i yxl The frequencies corresponding to the elements from top to bottom are-3f2, -2f2, -f2, 0, f2, 2f2, 3f2, and f2 is the low frequency.

[0085] Suppose the power frequency side injects a positive sequence small signal voltage disturbance with a frequency of f p , linearize the formula (7), and the expression of the small signal vector of the capacitor voltage of the M3C equivalent module is:

[0086]

[0087] Wherein,​ They are the small signal vector of the power frequency side component of the bridge arm current and the power frequency side control small signal vector respectively.

[0088] Equivalent module capacitance voltage small signal vector The frequency distribution of and the convolution process of formula (8) are as follows Figure 2 shown.

[0089] Equivalent module capacitance voltage small signal vector The phase sequence relationship of each frequency component in the u, v, and w phase sub-converters is shown in Table 3.

[0090] Table 3 Phase sequence relationship of the frequency component of the capacitor voltage small signal of the M3C equivalent module

[0091]

[0092] From Table 3, we can see that the equivalent module capacitor voltage small signal The frequency f of the frequency component coupled with the low frequency p +f2、f p -f2 is positive sequence and negative sequence in the u, v, and w phase sub-converters respectively, and the equivalent module capacitor voltage f p +f2、f p The -f2 small signal frequency component will be offset due to the phase sequence relationship from the perspective of the power frequency u, v, and w phases, and will not affect the dynamic characteristics of the M3C power frequency side.

[0093] Similarly, when the low-frequency side injection frequency is f p When the positive sequence small signal voltage is disturbed, the small signal frequency component coupled with the power frequency in the small signal frequency distribution of the equivalent module capacitor voltage will also be offset due to the phase sequence relationship, and the small signal frequency component coupled with the power frequency will not affect the dynamic characteristics of the low frequency side of M3C.

[0094] Substituting the small signal vector into equation (3) yields the bridge arm voltage small signal vector: expression:

[0095]

[0096] The equivalent module capacitor voltage small signal vector in formula (9) is Power frequency side control small signal vector Low-frequency side steady-state control signal vector m yxl , equivalent module capacitor voltage harmonic vector v cyx The frequency distribution obtained by convolution is as follows Figure 3 shown.

[0097] Bridge arm voltage small signal vector The phase sequence relationship of each frequency component of the bridge arm voltage in the u, v, w phase sub-converter is shown in Table 4.

[0098] Table 4 Small-signal frequency components and phase sequence relationship of M3C bridge arm voltage

[0099]

[0100] It can be obtained from Table 4 that the frequency components of the bridge arm voltage small-signal vector coupled with the low-frequency frequency f p +2f2, f p -2f2, f p +f1+f2, f p -f1-f2, f p +f1-f2, f p -f1+f2 are respectively negative sequence, positive sequence, positive sequence, negative sequence, negative sequence, and positive sequence in the u, v, w phase sub-converter, and the f p +2f2, f p -2f2, f p +f1+f2, f p -f1-f2, f p +f1-f2, f p -f1+f2 small-signal frequency components of the bridge arm voltage will be cancelled due to the phase sequence relationship in the power frequency u, v, w phase, and will not affect the dynamic characteristics of the M3C power frequency side. Similarly, when the low-frequency side injects a positive sequence small-signal voltage disturbance with a frequency of f p , the small-signal frequency components coupled with the power frequency in the small-signal frequency distribution of the bridge arm voltage will also be cancelled due to the phase sequence relationship, and will not affect the dynamic characteristics of the M3C low-frequency side.

[0101] Therefore, when the power / low-frequency side respectively injects a positive sequence small-signal voltage disturbance, the power and low-frequency frequency coupling generated by the M3C equivalent module capacitor voltage and the bridge arm voltage will not affect the dynamic characteristics of the M3C power / low-frequency side. Similarly, when the low-frequency side injects a positive sequence small-signal voltage disturbance with a frequency of f p , the small-signal frequency components coupled with the power frequency in the small-signal frequency distribution of the bridge arm voltage will also be cancelled due to the phase sequence relationship, and will not affect the dynamic characteristics of the M3C low-frequency side.

[0102] The application is directed to an innovative analysis method for the frequency coupling characteristics of a modular multilevel matrix converter (M3C) at power frequency and low frequency. Through theoretical modeling, frequency domain analysis and simulation verification, the generation path and cancellation mechanism of the coupled frequency components are revealed, significantly optimizing the dynamic performance and stability of the M3C system. By injecting positive sequence small signal voltage disturbances on the power frequency side and the low frequency side, and combining Fourier transform and frequency domain convolution analysis, the distribution law of the coupled frequency components in the bridge arm voltage and the equivalent module capacitor voltage is determined. The coupled frequency components are effectively canceled in the sub-converter due to the phase sequence asymmetry of the control signals on the power frequency side and the low frequency side (positive sequence / zero sequence complementary). By increasing the cascade sub-module capacitor or configuring an angle-connected transformer on the power / low frequency side, the current generated by the 3 times power / low frequency frequency components is suppressed, avoiding system oscillation or equipment overheating problems.

[0103] The M3C power / low frequency frequency coupling characteristic analysis method based on small signal frequency convolution analyzes whether there is a frequency coupling effect on the power / low frequency side of the M3C, determines the influence of the M3C bridge arm voltage and the equivalent module capacitor voltage on the power / low frequency side dynamic characteristics, solves the dynamic characteristic ambiguity problem caused by M3C multi-frequency coupling through frequency domain modeling and phase sequence cancellation mechanism, provides an effective technical path for harmonic suppression, stability improvement and control strategy optimization of complex converter systems, and is suitable for new energy grid-connected, flexible power transmission and other high-performance power electronic application scenarios.

[0104] Simulation verification:

[0105] Firstly, the bridge arm voltage steady-state harmonic characteristics and phase sequence relationship derived above are verified. Further, the frequency distribution of the M3C equivalent module capacitor voltage and the bridge arm voltage under small signal disturbance and the phase sequence relationship in each sub-converter are verified by injecting small signal voltage disturbance on the power frequency side of the M3C.

[0106] To verify the coupling characteristics of the M3C power / low frequency side equivalent module capacitor voltage and bridge arm voltage under steady state and under small signal disturbance, an M3C simulation model is built on the Matlab / Simulink simulation platform, and the model parameters are shown in Table 5.

[0107] Table 5 M3C simulation model parameters

[0108]

[0109] Secondly, M3C bridge arm voltage steady-state harmonic component verification: by adding the bridge arm voltages of phase a, phase b and phase c sub-converters in the simulation model and performing fast Fourier transform on them, the frequency spectrum of the phase a bridge arm voltage in the M3C can be obtained as shown in Figure 5. a b c Secondly, M3C bridge arm voltage steady-state harmonic component verification: by adding the bridge arm voltages of phase a, phase b and phase c sub-converters in the simulation model and performing fast Fourier transform on them, the frequency spectrum of the phase a bridge arm voltage in the M3C can be obtained as shown in Figure 5.​​Figure 4 As shown in the figure, it can be seen that there are no other harmonic components except 3f1 and 3f2 analyzed before; similarly, the u in M3C a 、u b 、u c By adding the bridge arm voltages of the phase sub-converters, the voltage spectrum of the equivalent module capacitor of phase a in M3C can be obtained as follows: Figure 5 As shown, it can be seen that there are no other harmonic components except 3f1 analyzed previously, which verifies the correctness of the M3C bridge arm voltage harmonic frequency distribution and phase sequence analysis.

[0110] Again, the M3C equivalent module capacitor voltage small signal disturbance frequency verification: by injecting a 20Hz small signal voltage disturbance to the M3C power frequency grid side, the u a 、u b 、u c The voltage spectrum of the capacitor of the equivalent module of the phase sub-converter is obtained by adding the voltage of the capacitor of the equivalent module of the phase sub-converter and performing fast Fourier transform on it. Figure 6 shown.

[0111] Consistent with the previous analysis, the voltage spectrum of the equivalent module capacitor of phase u in M3C has only f in addition to the steady-state harmonic component 2f1. p +f1、f p -f1 frequency component. It proves that when the power frequency side of M3C is disturbed by a small signal voltage, the small signal frequency component f of the equivalent module capacitor voltage is p +f2、f p -f2 will be cancelled out due to the phase sequence relationship from the perspective of the power frequency u, v, and w phases, and the frequency components coupled with the low-frequency phases will not affect the dynamic characteristics of the M3C power frequency side.

[0112] Furthermore, the frequency of the small signal disturbance of the M3C bridge arm voltage is verified: by injecting a 20Hz small signal voltage disturbance into the M3C power grid side, the u a 、v a 、w a The voltage spectrum of the u-phase bridge arm of the M3C power frequency side under the condition of small signal disturbance can be obtained by adding the voltage of the bridge arm of the phase sub-converter and performing fast Fourier transform. Figure 7 shown.

[0113] It can be seen that, consistent with the previous analysis, in addition to the steady-state fundamental component f1, the voltage spectrum of the u-phase bridge arm in M3C only has f p +2f1、f p -2f1、f pThe frequency component of the small signal voltage disturbance is coupled with the low frequency component of the bridge arm voltage. It is proved that the small signal frequency component of the bridge arm voltage coupled with the low frequency component will be cancelled out in the view of the u, v and w phase of the M3C power frequency side due to the phase sequence relationship, and will not affect the dynamic characteristics of the M3C power frequency side.

[0114] The application further discloses a computer program product comprising a computer program which, when executed by a processor, performs the steps of the method described above. The application further discloses a computer-readable storage medium having stored thereon a computer program which, when executed by a processor, performs the steps of the method described above. The application further discloses an M3C power frequency and low frequency frequency coupling characteristic analysis system comprising a memory and a processor connected to each other, wherein the memory has stored thereon a computer program which, when executed by the processor, performs the steps of the method described above. The product, medium and system of the application correspond to the method described above, and have the advantages of the method described above.

[0115] The application can realize all or part of the processes in the above-mentioned embodiment method, and can also be completed by computer program instruction related hardware. The computer program can be stored in a computer readable storage medium, and the computer program can realize the steps of the above-mentioned method embodiment when executed by a processor. The computer program includes computer program code, which can be in the form of source code, object code, executable files or some intermediate forms. The computer readable storage medium includes any entity or device capable of carrying computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal and software distribution medium, etc. The memory is used to store computer programs and / or modules, and the processor realizes various functions by running or executing the computer programs and / or modules stored in the memory, and calling data stored in the memory. The memory can include high-speed random access memory, and can also include non-volatile memory, such as hard disk, memory, plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, at least one magnetic disk storage device, flash memory device, or other volatile solid-state storage device, etc.

[0116] The above are only preferred embodiments of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiments. Any technical scheme falling within the concept of the present application shall fall within the protection scope of the present application. It should be noted that, for ordinary skilled in the art, some improvements and refinements without departing from the principles of the present application shall be considered as the protection scope of the present application.

Claims

1. A method for analyzing the coupling characteristics of M3C power frequency and low frequency, characterized in that: Including steps: Positive sequence small signal voltage disturbances are injected into the power frequency side and low frequency side of M3C respectively; Based on the positive sequence small signal voltage disturbance, a frequency domain response model of the M3C bridge arm voltage and the equivalent module capacitor voltage is established, and its frequency distribution is analyzed by Fourier transform; According to the phase sequence relationship of the control signals on the power frequency side and the low frequency side, the small signal frequency components in the bridge arm voltage and the equivalent module capacitor voltage that are coupled with the power frequency and the low frequency are determined; The coupling frequency component is offset by the phase sequence relationship of the control signals on the power frequency side and the low frequency side, so that the coupling frequency component has no effect on the dynamic characteristics of the power frequency side and the low frequency side of the M3C.

2. The M3C power frequency and low frequency coupling characteristic analysis method according to claim 1 is characterized in that: Based on the positive sequence small signal voltage disturbance, the frequency domain response model of the M3C bridge arm voltage and the equivalent module capacitor voltage is established. The specific process of analyzing its frequency distribution through Fourier transform is as follows: According to the average equivalent circuit of M3C, the bridge arm voltage of M3C is equivalent to: uyx=myxvcyx (1) Where, x is a, b, c, corresponding to phases a, b, and c on the low-frequency side of M3C respectively; y is u, v, and w, corresponding to phases u, v, and w on the power-frequency side of M3C respectively; uyx is the voltage of bridge arm yx; vcyx is the equivalent module capacitor voltage of bridge arm yx; myx is the total control signal of bridge arm yx; The overall control of M3C consists of the control of the power frequency side and the low frequency side. The control signal of M3C is divided into the power frequency side control signal and the low frequency side control signal. Equation (1) can be further rewritten as: Among them, myxh is the y-phase control signal on the power frequency side; myxl is the x-phase control signal on the low frequency side; By performing Fourier transform on the capacitor voltage, power frequency and low-frequency side control signals of the M3C equivalent module, the variables in equation (2) are described in the form of vectors. The expression of the M3C bridge arm voltage uyx in the frequency domain is written as: Among them, the frequency distribution of the industrial frequency side control signal myxh includes ±f1, the frequency distribution of the bridge arm equivalent module capacitor voltage vcyx includes ±2f1, ±(f1+f2), ±2f2, ±(f1-f2), and the frequency distribution of the low-frequency side control signal myxl includes ±f2.

3. The M3C power frequency and low frequency coupling characteristic analysis method according to claim 2 is characterized in that: The phase sequence relationship between the M3C power frequency and low-frequency control signals myxh and myxl in each sub-converter is: For the M3C power frequency and low-frequency control signal myxh, the phase sequence relationship within the a, b, c phase sub-converter is positive sequence, and the phase sequence relationship within the u, v, w phase sub-converter is zero sequence; For the M3C power frequency and low-frequency control signal myxl, the phase sequence relationship within the a, b, and c phase sub-converters is zero sequence, and the phase sequence relationship within the u, v, and w phase sub-converters is positive sequence.

4. The M3C power frequency and low frequency coupling characteristic analysis method according to claim 3 is characterized in that: The specific cancellation mechanism of the phase sequence relationship is as follows: when a disturbance is injected on the power frequency side, the positive and negative sequence components of the equivalent module capacitor voltage coupled with the low frequency are cancelled out from the perspective of the power frequency sub-converter; when a disturbance is injected on the low frequency side, the positive and negative sequence components of the bridge arm voltage coupled with the power frequency are cancelled out from the perspective of the low frequency sub-converter.

5. The M3C power frequency and low frequency coupling characteristic analysis method according to any one of claims 1 to 4, characterized in that: By increasing the capacitance of the cascaded sub-modules or setting a delta-connected transformer on the power frequency and low frequency sides, the impact of the three times power frequency and low frequency components on the system stability can be suppressed.

6. The M3C power frequency and low frequency coupling characteristic analysis method according to any one of claims 1 to 4, characterized in that: It also includes verification of the effectiveness of the cancellation mechanism, including harmonic spectrum analysis of the bridge arm voltage and equivalent module capacitor voltage in the simulation model.

7. The M3C power frequency and low frequency coupling characteristic analysis method according to claim 6, characterized in that: The specific process of verifying the effectiveness of the cancellation mechanism is as follows: building an M3C model in the simulation platform, analyzing the frequency spectrum of the bridge arm voltage and the equivalent module capacitor voltage through fast Fourier transform, and verifying that the amplitude of the coupling frequency component is lower than the preset threshold.

8. A computer program product comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are performed.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the computer program performs the steps of the method according to any one of claims 1 to 7.

10. An M3C power frequency and low frequency coupling characteristic analysis system, comprising a memory and a processor connected to each other, wherein a computer program is stored in the memory, characterized in that: When the computer program is executed by a processor, the computer program performs the steps of the method according to any one of claims 1 to 7.

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