CN112270075A - Small signal model analysis method for virtual synchronous machine of MMC interconnection converter - Google Patents

Small signal model analysis method for virtual synchronous machine of MMC interconnection converter Download PDF

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CN112270075A
CN112270075A CN202011097782.7A CN202011097782A CN112270075A CN 112270075 A CN112270075 A CN 112270075A CN 202011097782 A CN202011097782 A CN 202011097782A CN 112270075 A CN112270075 A CN 112270075A
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mmc
synchronous machine
signal model
virtual
interconnection converter
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CN112270075B (en
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冯仰敏
王恩南
杨沛豪
王羚宇
高峰
韩毅
常洋涛
杨洋
宋子琛
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Xian Thermal Power Research Institute Co Ltd
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Xian Thermal Power Research Institute Co Ltd
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/20—Design optimisation, verification or simulation
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2113/00—Details relating to the application field
    • G06F2113/04—Power grid distribution networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Abstract

The invention discloses a small signal model analysis method for a virtual synchronous machine of an MMC interconnection converter, which comprises the following steps of: starting from an alternating-current side angle of an MMC interconnection converter of an alternating-current and direct-current hybrid micro-grid to obtain a voltage equation; establishing an MMC interconnection converter power output equation; establishing an expression of an output complex power S of the MMC interconnection converter; establishing an active power small signal model and a reactive power small signal model; a virtual synchronous machine control mechanical equation and a virtual synchronous machine reactive power excitation control equation based on a power transmission principle; establishing a small signal model of virtual control; defining a parameter matrix according to the small signal model of virtual control; obtaining a small signal model of the virtual synchronous machine system of the MMC interconnection converter in a stable operation state; analyzing the influence of the virtual moment of inertia J on the stability of the control system; and analyzing the influence of the virtual damping coefficient D on the stability of the control system. According to the invention, the stability of the virtual synchronous machine control system of the MMC interconnection converter is verified by researching the root track of the virtual parameters.

Description

Small signal model analysis method for virtual synchronous machine of MMC interconnection converter
Technical Field
The invention relates to a small signal model analysis method for a virtual synchronous machine of an MMC interconnection converter, which verifies the stability of a virtual synchronous machine control system of the MMC interconnection converter by researching a virtual parameter root track.
Background
An MMC interconnection converter interface converter in an alternating current-direct current hybrid micro-grid generally adopts droop control, the conventional droop control does not have inertia and damping links, the high permeability of a distributed power supply cannot be maintained, and a Virtual Synchronous Generator (VSG) can provide inertia and damping support for a system by simulating the characteristics of a Synchronous generator, so that primary frequency modulation and primary voltage regulation are realized. In the transient transformation process of the virtual synchronous machine, the buffer energy variation is represented by virtual moment of inertia J variation, and various frictional resistances are represented by virtual damping coefficient D variation. In order to verify the stability of the virtual synchronous machine control system of the MMC interconnection converter of the alternating current-direct current hybrid micro-grid, the stability of the virtual synchronous machine control system needs to be researched.
Disclosure of Invention
The invention provides a small signal model analysis method for a virtual synchronous machine of an MMC interconnection converter, which comprises the steps of firstly establishing a virtual synchronous machine control model of the MMC interconnection converter of a hybrid micro-grid based on a power transmission principle; then analyzing a small signal model of the virtual synchronous machine for transmitting active power and reactive power; then analyzing a small signal model controlled by the virtual synchronous machine; and finally, verifying the stability of the virtual synchronous machine control system of the MMC interconnection converter by researching the root track of the virtual parameters.
The invention is realized by adopting the following technical scheme:
a small signal model analysis method for a virtual synchronous machine of an MMC interconnection converter comprises the following steps:
1) starting from an alternating-current side angle of an MMC interconnection converter of an alternating-current and direct-current hybrid micro-grid to obtain a voltage equation;
2) establishing a power output equation of the MMC interconnection converter according to the AC side voltage equation of the MMC interconnection converter in the step 1);
3) establishing an expression of the output complex power S of the MMC interconnection converter according to the power transmission equation of the MMC interconnection converter in the step 2);
4) establishing an active power small signal model and a reactive power small signal model according to the expression of the complex power S output by the MMC interconnection converter in the step 3);
5) according to the method, according to the fact that instantaneous active power variation of an alternating-current micro-grid and a direct-current micro-grid are the same in an MMC interconnection converter control system of an alternating-current and direct-current hybrid micro-grid, the characteristic of a synchronous machine is injected into the MMC interconnection converter control system, and a virtual synchronous machine control mechanical equation and a virtual synchronous machine reactive power excitation control equation based on a power transmission principle are obtained;
6) controlling a mechanical equation according to the virtual synchronous machine based on the power transmission principle in the step 5), and establishing a small signal model of virtual control;
7) defining a parameter matrix according to the small signal model virtually controlled in the step 6);
8) combining the active power small-signal model and the reactive power small-signal model in the step 4), the small-signal model virtually controlled in the step 6) and the parameter matrix in the step 7) to obtain a small-signal model when the virtual synchronous machine system of the MMC interconnection converter is in a stable operation state;
9) according to the small signal model of the MMC interconnection converter virtual synchronous machine system in the stable operation state in the step 8), drawing a root track change diagram of the virtual moment of inertia J, and analyzing the influence of the virtual moment of inertia J on the stability of the control system;
10) and according to the small signal model of the MMC interconnection converter virtual synchronous machine system in the stable running state in the step 8), drawing a root track change diagram of the virtual damping coefficient D, and analyzing the influence of the virtual damping coefficient D on the stability of the control system.
The further improvement of the invention is that step 1) starts from the angle of the alternating current side of the MMC interconnection converter of the alternating current-direct current hybrid micro-grid to obtain a voltage equation,
Figure BDA0002724317640000021
wherein:
Figure BDA0002724317640000022
for AC mains voltage e0A corresponding vector;
Figure BDA0002724317640000023
for MMC interconnected converter AC side voltage UacA corresponding vector;
Figure BDA0002724317640000024
for alternating mains current i0The corresponding vector.
The further improvement of the invention is that the specific implementation method of the step 2) is as follows: establishing a power transmission equation of the MMC interconnection converter according to the voltage equation of the AC side of the MMC interconnection converter in the step 1):
Figure BDA0002724317640000031
wherein: rf、XfThe resistance value and the inductive reactance of the filter circuit; delta is the AC mains voltage vector
Figure BDA0002724317640000032
AC side voltage vector of converter interconnected with MMC
Figure BDA0002724317640000033
The phase angle difference between them; AC mains voltage e0Can be analogous to the armature electromotive force of synchronous motor; AC side voltage U of MMC interconnection converteracAnalogous to synchronous machine terminal voltage; synchronous motor based on armature electromotive force and terminal voltage phase anglePositive and negative of the difference, i.e., as a motor or generator; similarly, in the alternating current-direct current hybrid micro-grid MMC interconnection converter control system, power bidirectional flow is realized by controlling delta positive and negative; when the delta is greater than 0, the data is converted into a binary data,
Figure BDA0002724317640000034
advance in
Figure BDA0002724317640000035
The MMC interconnection converter operates in an inversion mode, and power is transmitted from the direct-current micro-grid to the alternating-current micro-grid; when the delta is less than 0, the crystal grain size is more than zero,
Figure BDA0002724317640000036
hysteresis
Figure BDA0002724317640000037
The MMC interconnection converter operates in a rectification mode, and power is transmitted from the alternating-current micro-grid to the direct-current micro-grid; when the delta is equal to 0, the second phase is zero,
Figure BDA0002724317640000038
and
Figure BDA0002724317640000039
and in the same phase, no power is exchanged between the alternating current micro-grid and the direct current micro-grid.
The further improvement of the invention is that the specific implementation method of the step 3) is as follows: according to the power transmission equation of the MMC interconnection converter in the step 2), establishing an expression of the output complex power S of the MMC interconnection converter:
Figure BDA00027243176400000310
the further improvement of the invention is that the specific implementation method of the step 4) is as follows: establishing an active power small signal model and a reactive power small signal model according to the expression of the complex power S output by the MMC interconnection converter in the step 3):
Figure BDA00027243176400000311
Figure BDA0002724317640000041
the further improvement of the invention is that the concrete implementation method of the step 5) is as follows: according to the mixed little electric wire netting MMC interconnection converter control system of alternating current-direct current, alternating current little electric wire netting, direct current little electric wire netting instantaneous active power variation are the same, inject the synchronous machine characteristic at MMC interconnection converter control system, obtain the virtual synchronous machine control mechanical equation based on power transmission principle:
Figure BDA0002724317640000042
wherein: j is a virtual moment of inertia; the current value of the side angular frequency of the alternating-current microgrid is obtained; the initial value of the side angular frequency of the alternating-current micro-grid is obtained; d is a virtual damping coefficient; k is a radical ofudcThe droop adjusting coefficient of the direct current micro-grid is obtained; u shapedcThe current value is the current value of the bus voltage at the direct current side; u shapedc0The initial value of the DC side bus voltage is obtained; cdcIs a DC side capacitance value; in the control of the virtual synchronous machine of the MMC interconnection converter, the active power regulation control of the AC-DC hybrid micro-grid is realized by directly controlling the AC frequency and the DC voltage, and the active load of the hybrid micro-grid is balanced; when the mixed little electric wire netting MMC interconnection of alternating current-direct current transform transverter power regulating variable does not have undulant, control system steady state operation promptly, alternating current frequency and direct current voltage reach the stable value, exist:
Figure BDA0002724317640000043
the virtual synchronous machine induction internal potential consists of two parts: one part is idle load, the idle load electromotive force corresponding to the virtual excitation voltage is generated by the reactive power deviation, and the virtual synchronous machine reactive excitation control equation is a virtual synchronous machine reactive excitation control equation: e ═ E0+kq(Qref-Q); wherein: e is an effective value of the induced internal potential of the virtual synchronous machine; e0Is an excitation no-load electromotive force effective value; k is a radical ofqThe reactive voltage droop control coefficient is obtained; qrefIs a reactive power reference value; q is the current value of reactive power; synthesis ofVirtual rotor angular frequency and phase angle difference delta obtained by virtual synchronous machine active frequency control calculation are obtained, and three-phase voltage modulation signals of an equivalent alternating current output port of an alternating current-direct current hybrid micro-grid MMC interconnection converter are obtained
Figure BDA0002724317640000044
The further improvement of the invention is that the specific implementation method of the step 6) is as follows: controlling a mechanical equation according to the virtual synchronous machine based on the power transmission principle in the step 5), and establishing a small signal model of virtual control:
Figure BDA0002724317640000051
the further improvement of the invention is that the specific implementation method of the step 7) is as follows: defining a parameter matrix according to the small signal model virtually controlled in the step 6): y ═ delta ', delta U'ac，Δδ，ΔUac) (ii) a Wherein: delta delta 'is the derivative of Delta delta, Delta U'acIs to Δ UacThe derivative of (c).
The further improvement of the invention is that the specific implementation method of the step 8) is as follows: combining the active power small-signal model and the reactive power small-signal model in the step 4), the small-signal model virtually controlled in the step 6) and the parameter matrix in the step 7), and obtaining the small-signal model when the virtual synchronous machine system of the MMC interconnection converter is in a stable operation state:
Figure BDA0002724317640000052
the expressions of the variables a, b, c, d are:
Figure BDA0002724317640000053
the further improvement of the invention is that the specific implementation method of the step 9) is as follows: according to the small signal model of the MMC interconnection converter virtual synchronous machine system in the stable operation state in the step 8), drawing a root track change diagram of the virtual moment of inertia J, and analyzing the influence of the virtual moment of inertia J on the stability of the control system;
the specific implementation method of the step 10) comprises the following steps: according to the small signal model of the MMC interconnection converter virtual synchronous machine system in the stable operation state in the step 8), drawing a root track change diagram of a virtual damping coefficient D, and analyzing the influence of the virtual damping coefficient D on the stability of the control system; as D increases, the system gradually goes to steady state.
Compared with the prior art, the invention has at least the following beneficial technical effects:
1. the invention provides a small-signal model analysis method for a virtual synchronous machine of an MMC interconnection converter, which is used for verifying the stability of a control model of the virtual synchronous machine based on a power transmission principle and is more suitable for a control system of the MMC interconnection converter of a hybrid micro-grid.
2. The method respectively verifies the influence of the virtual moment of inertia and the virtual damping coefficient on the stability of the virtual synchronous machine control system by analyzing four characteristic roots of the small signal model.
Drawings
FIG. 1 is a topological diagram of a main circuit of an MMC interconnection converter;
FIG. 2 is a control block diagram of a virtual synchronous machine of an MMC interconnection converter based on a power transmission principle;
FIG. 3 is a graph of root locus variation of a virtual moment of inertia J;
fig. 4 is a graph showing a change in root locus of the virtual damping coefficient D.
Detailed Description
The technical solution of the present invention is further described in detail by the accompanying drawings.
As shown in fig. 1, starting from an ac-side angle of an ac-dc hybrid micro-grid MMC interconnection converter, an ac-side voltage equation can be expressed as:
Figure BDA0002724317640000061
in formula (1):
Figure BDA0002724317640000062
for AC mains voltage e0A corresponding vector;
Figure BDA0002724317640000063
for MMC interconnected converter AC side voltage UacA corresponding vector;
Figure BDA0002724317640000064
for alternating mains current i0The corresponding vector. The MMC interconnection converter power transfer equation can be expressed as:
Figure BDA0002724317640000065
in formula (2): rf、XfThe resistance value and the inductive reactance of the filter circuit; delta is the AC mains voltage vector
Figure BDA0002724317640000066
AC side voltage vector of converter interconnected with MMC
Figure BDA0002724317640000067
The phase angle difference between them. The voltage equation and the power transmission equation on the alternating current side of the MMC interconnection converter described by the formula (1) and the formula (2) can be respectively analogized to the voltage equation and the power equation of a synchronous motor. AC mains voltage e0Can be analogous to the armature electromotive force of synchronous motor; AC side voltage U of MMC interconnection converteracAnalogous to synchronous machine terminal voltage. The synchronous machine can be used as a motor or a generator according to the positive and negative of the phase angle difference between the armature electromotive force and the terminal voltage. Similarly, in the alternating current-direct current hybrid micro-grid MMC interconnection converter control system, power bidirectional flow is realized by controlling delta positive and negative. When the delta is greater than 0, the data is converted into a binary data,
Figure BDA0002724317640000071
advance in
Figure BDA0002724317640000072
The MMC interconnection converter operates in an inversion mode, and power is transmitted from the direct-current micro-grid to the alternating-current micro-grid; when the delta is less than 0, the crystal grain size is more than zero,
Figure BDA0002724317640000073
hysteresis
Figure BDA0002724317640000074
The MMC interconnection converter operates in a rectification mode, and power is transmitted from the alternating-current micro-grid to the direct-current micro-grid; when the delta is equal to 0, the second phase is zero,
Figure BDA0002724317640000075
and
Figure BDA0002724317640000076
and in the same phase, no power is exchanged between the alternating current micro-grid and the direct current micro-grid.
According to the power transmission equation of the MMC interconnection converter in the formula (2), the expression of the complex power S output by the system can be obtained as follows:
Figure BDA0002724317640000077
then the active small signal models transmitted by the system are respectively:
Figure BDA0002724317640000078
the reactive small signal models of the system transmission are respectively as follows:
Figure BDA0002724317640000079
as shown in fig. 2, in the ac/dc hybrid microgrid MMC interconnection converter control system, the instantaneous active power variation of the ac microgrid and the dc microgrid is the same, and a virtual synchronous machine control mechanical equation based on the power transmission principle can be obtained as follows:
Figure BDA00027243176400000710
in formula (6): j is a virtual moment of inertia; the current value of the side angular frequency of the alternating-current microgrid is obtained; is a.c.A micro-grid side angular frequency initial value; d is a virtual damping coefficient; k is a radical ofudcThe droop adjusting coefficient of the direct current micro-grid is obtained; u shapedcThe current value is the current value of the bus voltage at the direct current side; u shapedc0The initial value of the DC side bus voltage is obtained; cdcIs a dc side capacitance value. The active power regulation control of the alternating current-direct current hybrid micro-grid can be realized by directly controlling the alternating current frequency and the direct current voltage in the virtual synchronous machine control of the MMC interconnection converter, and the active load of the hybrid micro-grid is balanced.
When the mixed little electric wire netting MMC interconnection of alternating current-direct current transform transverter power regulating variable does not have undulant, control system steady state operation promptly, alternating current frequency and direct current voltage reach the stable value, exist:
Figure BDA0002724317640000081
the virtual synchronous machine induction internal potential consists of two parts: when one part is no-load, the virtual excitation voltage is corresponding to the no-load electromotive force, and the other part is generated by the reactive power deviation, and the virtual synchronous machine reactive excitation control equation is as follows:
E＝E0+kq(Qref-Q) (8)
in formula (8): e is an effective value of the induced internal potential of the virtual synchronous machine; e0Is an excitation no-load electromotive force effective value; k is a radical ofqThe reactive voltage droop control coefficient is obtained; qrefIs a reactive power reference value; q is the current value of reactive power.
The three-phase voltage modulation signal of the equivalent alternating current output port of the MMC interconnection converter of the alternating current-direct current hybrid micro-grid can be obtained by synthesizing the virtual rotor angular frequency and the phase angle difference delta obtained by the active frequency control calculation of the virtual synchronous machine
Figure BDA0002724317640000082
When the MMC interconnection converter virtual synchronous machine system is in a stable grid-connected operation state, the system is set as yes. The droop control of the alternating-current and direct-current hybrid micro-grid is converted into active output variable quantity, and the direct-current voltage reaches a stable value. Combining equation (6) and equation (7), the small signal model for virtual control can be derived as:
Figure BDA0002724317640000083
defining the matrix Y as:
Y＝(Δδ′，ΔU′ac，Δδ，ΔUac) (10)
in formula (10): delta delta 'is the derivative of Delta delta, Delta U'acIs to Δ UacThe derivative of (3) and the small signal model obtained by combining the formula (4), the formula (5) and the formula (9) when the virtual synchronous machine system of the MMC interconnection converter is in the stable operation state are as follows:
Figure BDA0002724317640000091
in the formula (11), the variables a, b, c and d are expressed as follows:
Figure BDA0002724317640000092
as shown in fig. 3, according to the small signal model of the MMC interconnection converter in the stable operation state, the root trajectory change diagram, s, of the virtual moment of inertia J can be drawn1、s2、s3、s4Is four characteristic roots of a system small signal model, wherein s1、s2The method is a dominant characteristic root of the system and plays a main influence role on the dynamic performance of the system; s3、s4On the real axis, the system has no change basically and does not influence the system dynamics. The arrow direction is the variation trend of the dominant characteristic root along with the increase of the parameter. The change of J from an over-damped state to an under-damped state means that the system gradually transitions to an unstable state as J increases, but too small a J results in a system lacking inertial characteristics.
As shown in FIG. 4, according to the small signal model of the MMC interconnection converter virtual synchronous machine system in the stable operation state, the root rail of the virtual damping coefficient D can be drawnTrace change diagram, s1、s2、s3、s4Is four characteristic roots of a system small signal model, wherein s1、s2The method is a dominant characteristic root of the system and plays a main influence role on the dynamic performance of the system; s3、s4On the real axis, the system has no change basically and does not influence the system dynamics. The arrow direction is the variation trend of the dominant characteristic root along with the increase of the parameter. D is changed from an underdamped state to an overdamped state, which shows that the system gradually tends to a stable state along with the increase of D.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, changes and equivalent structural changes made to the above embodiment according to the technical spirit of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims (10)

1. A small signal model analysis method for a virtual synchronous machine of an MMC interconnection converter is characterized by comprising the following steps of:
1) starting from an alternating-current side angle of an MMC interconnection converter of an alternating-current and direct-current hybrid micro-grid to obtain a voltage equation;
2) establishing a power output equation of the MMC interconnection converter according to the AC side voltage equation of the MMC interconnection converter in the step 1);
3) establishing an expression of the output complex power S of the MMC interconnection converter according to the power transmission equation of the MMC interconnection converter in the step 2);
4) establishing an active power small signal model and a reactive power small signal model according to the expression of the complex power S output by the MMC interconnection converter in the step 3);
5) according to the method, according to the fact that instantaneous active power variation of an alternating-current micro-grid and a direct-current micro-grid are the same in an MMC interconnection converter control system of an alternating-current and direct-current hybrid micro-grid, the characteristic of a synchronous machine is injected into the MMC interconnection converter control system, and a virtual synchronous machine control mechanical equation and a virtual synchronous machine reactive power excitation control equation based on a power transmission principle are obtained;
6) controlling a mechanical equation according to the virtual synchronous machine based on the power transmission principle in the step 5), and establishing a small signal model of virtual control;
7) defining a parameter matrix according to the small signal model virtually controlled in the step 6);
8) combining the active power small-signal model and the reactive power small-signal model in the step 4), the small-signal model virtually controlled in the step 6) and the parameter matrix in the step 7) to obtain a small-signal model when the virtual synchronous machine system of the MMC interconnection converter is in a stable operation state;
9) according to the small signal model of the MMC interconnection converter virtual synchronous machine system in the stable operation state in the step 8), drawing a root track change diagram of the virtual moment of inertia J, and analyzing the influence of the virtual moment of inertia J on the stability of the control system;
10) and according to the small signal model of the MMC interconnection converter virtual synchronous machine system in the stable running state in the step 8), drawing a root track change diagram of the virtual damping coefficient D, and analyzing the influence of the virtual damping coefficient D on the stability of the control system.
2. The small-signal model analysis method for the MMC interconnection converter virtual synchronous machine according to claim 1, characterized in that step 1) starts from an angle of an alternating current side of an MMC interconnection converter of an alternating current-direct current hybrid micro-grid to obtain a voltage equation,
Figure FDA0002724317630000021
wherein:
Figure FDA0002724317630000022
for AC mains voltage e0A corresponding vector;
Figure FDA0002724317630000023
for MMC interconnected converter AC side voltage UacA corresponding vector;
Figure FDA0002724317630000024
for alternating mains current i0The corresponding vector.
3. According toThe method for analyzing the small-signal model of the virtual synchronous machine of the MMC interconnection converter as set forth in claim 2, wherein the step 2) is specifically realized by the following steps: establishing a power transmission equation of the MMC interconnection converter according to the voltage equation of the AC side of the MMC interconnection converter in the step 1):
Figure FDA0002724317630000025
wherein: rf、XfThe resistance value and the inductive reactance of the filter circuit; delta is the AC mains voltage vector
Figure FDA0002724317630000026
AC side voltage vector of converter interconnected with MMC
Figure FDA0002724317630000027
The phase angle difference between them; AC mains voltage e0Can be analogous to the armature electromotive force of synchronous motor; AC side voltage U of MMC interconnection converteracAnalogous to synchronous machine terminal voltage; the synchronous motor is used as a motor or a generator according to the positive and negative of the phase angle difference between the armature electromotive force and the terminal voltage; similarly, in the alternating current-direct current hybrid micro-grid MMC interconnection converter control system, power bidirectional flow is realized by controlling delta positive and negative; when the delta is greater than 0, the data is converted into a binary data,
Figure FDA0002724317630000028
advance in
Figure FDA0002724317630000029
The MMC interconnection converter operates in an inversion mode, and power is transmitted from the direct-current micro-grid to the alternating-current micro-grid; when the delta is less than 0, the crystal grain size is more than zero,
Figure FDA00027243176300000210
hysteresis
Figure FDA00027243176300000211
The MMC interconnection converter operates in a rectification mode, and power is transmitted from the alternating current micro-grid to the direct current micro-gridInputting; when the delta is equal to 0, the second phase is zero,
Figure FDA00027243176300000212
and
Figure FDA00027243176300000213
and in the same phase, no power is exchanged between the alternating current micro-grid and the direct current micro-grid.
4. The MMC interconnection converter virtual synchronous machine small-signal model analysis method according to claim 3, wherein the specific implementation method of step 3) is as follows: according to the power transmission equation of the MMC interconnection converter in the step 2), establishing an expression of the output complex power S of the MMC interconnection converter:
Figure FDA00027243176300000214
5. the MMC interconnection converter virtual synchronous machine small-signal model analysis method according to claim 4, characterized in that the specific implementation method of step 4) is as follows: establishing an active power small signal model and a reactive power small signal model according to the expression of the complex power S output by the MMC interconnection converter in the step 3):
Figure FDA0002724317630000031
6. the MMC interconnection converter virtual synchronous machine small-signal model analysis method according to claim 5, wherein the specific implementation method of step 5) is as follows: according to the mixed little electric wire netting MMC interconnection converter control system of alternating current-direct current, alternating current little electric wire netting, direct current little electric wire netting instantaneous active power variation are the same, inject the synchronous machine characteristic at MMC interconnection converter control system, obtain the virtual synchronous machine control mechanical equation based on power transmission principle:
Figure FDA0002724317630000032
wherein: j is a virtual moment of inertia; the current value of the side angular frequency of the alternating-current microgrid is obtained; the initial value of the side angular frequency of the alternating-current micro-grid is obtained; d is a virtual damping coefficient; k is a radical ofudcThe droop adjusting coefficient of the direct current micro-grid is obtained; u shapedcThe current value is the current value of the bus voltage at the direct current side; u shapedc0The initial value of the DC side bus voltage is obtained; cdcIs a DC side capacitance value; in the control of the virtual synchronous machine of the MMC interconnection converter, the active power regulation control of the AC-DC hybrid micro-grid is realized by directly controlling the AC frequency and the DC voltage, and the active load of the hybrid micro-grid is balanced; when the mixed little electric wire netting MMC interconnection of alternating current-direct current transform transverter power regulating variable does not have undulant, control system steady state operation promptly, alternating current frequency and direct current voltage reach the stable value, exist:
Figure FDA0002724317630000033
the virtual synchronous machine induction internal potential consists of two parts: one part is idle load, the idle load electromotive force corresponding to the virtual excitation voltage is generated by the reactive power deviation, and the virtual synchronous machine reactive excitation control equation is a virtual synchronous machine reactive excitation control equation: e ═ E0+kq(Qref-Q); wherein: e is an effective value of the induced internal potential of the virtual synchronous machine; e0Is an excitation no-load electromotive force effective value; k is a radical ofqThe reactive voltage droop control coefficient is obtained; qrefIs a reactive power reference value; q is the current value of reactive power; synthesizing virtual rotor angular frequency and phase angle difference delta obtained by active frequency control calculation of a virtual synchronous machine to obtain a three-phase voltage modulation signal of an equivalent alternating current output port of an alternating current-direct current hybrid micro-grid MMC interconnection converter
Figure FDA0002724317630000041
7. The MMC interconnection converter virtual synchronous machine small-signal model analysis method according to claim 6, wherein the step 6) is implemented by: controlling a virtual synchronous machine based on the power transmission principle according to the step 5)And (3) establishing a small signal model of virtual control by using a mechanical equation:
Figure FDA0002724317630000042
8. the method for analyzing the small-signal model of the MMC interconnection converter virtual synchronous machine according to claim 7, wherein the step 7) is realized by the following steps: defining a parameter matrix according to the small signal model virtually controlled in the step 6): y ═ delta ', delta U'ac，Δδ，ΔUac) (ii) a Wherein: delta delta 'is the derivative of Delta delta, Delta U'acIs to Δ UacThe derivative of (c).
9. The method for analyzing the small-signal model of the virtual synchronous machine of the MMC interconnection converter according to claim 8, wherein the step 8) is specifically realized by the following steps: combining the active power small-signal model and the reactive power small-signal model in the step 4), the small-signal model virtually controlled in the step 6) and the parameter matrix in the step 7), and obtaining the small-signal model when the virtual synchronous machine system of the MMC interconnection converter is in a stable operation state:
Figure FDA0002724317630000043
the expressions of the variables a, b, c, d are:
Figure FDA0002724317630000044
10. the method for analyzing the small-signal model of the virtual synchronous machine of the MMC interconnection converter according to claim 9, wherein the step 9) is specifically realized by: according to the small signal model of the MMC interconnection converter virtual synchronous machine system in the stable operation state in the step 8), drawing a root track change diagram of the virtual moment of inertia J, and analyzing the influence of the virtual moment of inertia J on the stability of the control system;
the specific implementation method of the step 10) comprises the following steps: according to the small signal model of the MMC interconnection converter virtual synchronous machine system in the stable operation state in the step 8), drawing a root track change diagram of a virtual damping coefficient D, and analyzing the influence of the virtual damping coefficient D on the stability of the control system; as D increases, the system gradually goes to steady state.
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