CN113346781A - Passive consistency control method for grid-connected current of modular multilevel converter - Google Patents

Passive consistency control method for grid-connected current of modular multilevel converter Download PDF

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CN113346781A
CN113346781A CN202110734879.2A CN202110734879A CN113346781A CN 113346781 A CN113346781 A CN 113346781A CN 202110734879 A CN202110734879 A CN 202110734879A CN 113346781 A CN113346781 A CN 113346781A
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mmc
passive
consistency
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CN113346781B (en
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薛花
王育飞
田广平
扈曾辉
陈程
杨兴武
刘波
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Shanghai Electric Power University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • 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
    • H02J3/40—Synchronising a generator for connection to a network or to another generator
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/539—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency
    • H02M7/5395—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency by pulse-width modulation
    • 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
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin

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Abstract

The invention relates to a passive consistency control method for modular multilevel grid-connected current, which comprises the following steps: establishing MMC grid-connected current under the condition of unbalanced power grid voltage, and designing an expected global energy function of an MMC grid-connected system to obtain a PCHD model of the MMC grid-connected system under the condition of unbalanced power grid voltage; based on a PCHD model of an MMC grid-connected system, a consistency method is combined to construct an MMC grid-connected passive consistency controller based on the PCHD model under the condition of unbalanced network voltage so as to obtain a control quantity; processing the control quantity by adopting a pulse modulation method to obtain a corresponding trigger pulse signal; and controlling the switching state of the converter of each phase bridge arm submodule of the MMC according to the trigger pulse signal. Compared with the prior art, the method disclosed by the invention is combined with the PCHD model and the consistency method to realize independent synchronous control of the MMC grid-connected positive and negative sequence subsystems, has the advantages of simple control law form, no singular point and good stability, and can effectively improve the synchronous tracking effect of the grid-connected current.

Description

Passive consistency control method for grid-connected current of modular multilevel converter
Technical Field
The invention relates to the technical field of control of modular multilevel converters, in particular to a passive consistency control method for grid-connected current of a modular multilevel converter.
Background
The Modular Multilevel Converter (MMC) is a Multilevel Converter capable of realizing high-voltage and medium-voltage power conversion without a transformer, and the MMC is widely applied to the field of large-scale renewable energy grid connection at present, however, when a single-phase short circuit occurs in a power grid, because a system alternating current can generate a negative sequence component, power oscillation is caused, stable operation of an MMC grid-connected system is finally influenced, and system instability can be caused in a severe case.
Therefore, the MMC grid-connected current needs to be controlled to achieve MMC grid-connected current balance, a vector control method is mostly adopted for control in the prior art, the method is designed for a controller aiming at the nonlinear essence of an MMC grid-connected current system, and the energy is not used, so that when an uncertain disturbance condition exists, the disturbance resistance and robustness of a vector controller face challenges; compared with the traditional vector control method, the prior art is based on a nonlinear control method, and a controller capable of reflecting the nonlinear essence of an MMC grid-connected current system is designed from the energy perspective, the method can improve the control performance of the closed-loop control system in terms of stability and robustness to a certain extent, but is complex in calculation, and cannot solve the problem that the correlation in positive-sequence and negative-sequence current subsystems influences the passive control dynamic tracking performance, so that the control synchronism of the positive-sequence and negative-sequence independent subsystems cannot be ensured, and the synchronous stable tracking of the positive-sequence and negative-sequence systems cannot be reliably realized.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a modularized multi-level grid-connected current passive consistency control method to ensure the synchronous stable tracking of a positive sequence double system and a negative sequence double system.
The purpose of the invention can be realized by the following technical scheme: a passive consistency control method for modular multilevel grid-connected current comprises the following steps:
s1, establishing MMC grid-connected current under the condition of unbalanced grid voltage, and designing an expected global energy function of the MMC grid-connected system to obtain a PCHD (port controlled Hamilton with dispersion) model of the MMC grid-connected system under the condition of unbalanced grid voltage;
s2, constructing a PCHD model-based MMC grid-connected system PCHD model based on the step S1, and combining a consistency method to obtain a controlled variable, wherein the PCHD model-based MMC grid-connected passive consistency controller is based on the PCHD model under the condition of unbalanced power grid voltage;
s3, processing the control quantity by adopting a pulse modulation method to obtain a corresponding trigger pulse signal;
and S4, controlling the switching state of the converter of each phase bridge arm submodule of the MMC according to the trigger pulse signal.
Further, the step S1 specifically includes the following steps:
s11, under the dq rotation coordinate system, defining the state variable as
Figure BDA0003141235510000021
Defining input variables as
Figure BDA0003141235510000022
Figure BDA0003141235510000023
Defining an output variable as
Figure BDA0003141235510000024
Wherein the positive sequence subsystem state variable is
Figure BDA0003141235510000025
Figure BDA0003141235510000026
Negative sequence subsystem state variables of
Figure BDA0003141235510000027
The positive sequence subsystem input variable is
Figure BDA0003141235510000028
Negative sequence subsystem input variables are
Figure BDA0003141235510000029
Figure BDA00031412355100000210
The positive sequence subsystem output variable is
Figure BDA00031412355100000211
The negative sequence subsystem output variable is
Figure BDA00031412355100000212
Wherein L iseqIs the inductance of the bridge arm,
Figure BDA00031412355100000213
respectively the dq axis positive and negative sequence components of the output voltage at the AC side,
Figure BDA00031412355100000214
are the dq axis positive and negative sequence components of the ac side supply current,
Figure BDA00031412355100000215
Figure BDA00031412355100000216
the dq axis positive and negative sequence components of the AC side power supply voltage are respectively;
s12, establishing an MMC grid-connected current state equation based on the PCHD model based on the state variable, the input variable and the output variable in the step S11, designing an expected global energy function of the MMC grid-connected system, and obtaining the PCHD model of the MMC grid-connected system under the condition of unbalanced power grid voltage.
Further, the MMC grid-connected current state equation specifically includes:
Figure BDA00031412355100000217
Figure BDA00031412355100000218
Figure BDA00031412355100000219
Figure BDA00031412355100000220
Figure BDA0003141235510000031
Figure BDA0003141235510000032
Figure BDA0003141235510000033
Figure BDA0003141235510000034
Figure BDA0003141235510000035
wherein the content of the first and second substances,j (x) is an interconnection matrix, R (x) is a damping matrix, g (x) is a port matrix, H (x) is an energy function, omega is a fundamental angular frequency, R is a bridge arm resistance,
Figure BDA0003141235510000036
is a differential operator.
Further, the desired global energy function is specifically:
Figure BDA0003141235510000037
Figure BDA0003141235510000038
Figure BDA0003141235510000039
Figure BDA00031412355100000310
Figure BDA00031412355100000311
wherein x is*Is the desired trajectory for x and is,
Figure BDA00031412355100000312
respectively are the expected positive and negative sequence components of the dq axis of the alternating-current side power supply current, and D is a bridge arm inductance matrix.
Further, the PCHD model of the MMC grid-connected system under the unbalanced power grid voltage specifically comprises:
Figure BDA00031412355100000313
Figure BDA00031412355100000314
Figure BDA00031412355100000315
wherein, Jd(x) Expect an interconnection matrix for the system, Rd(x) Desired damping matrix for the system, Ja(x)、Ra(x) Respectively an injected dissipation matrix and a damping matrix.
Further, the step S2 specifically includes the following steps:
s21, setting Laplacian matrix L of positive sequence subsystem and negative sequence subsystem of MMC grid-connected system by combining consistency method1、L2；
S22, taking the difference between the state variable and the expected balance point as a control target, substituting the grid-connected current state variable error into a PCHD model-based passive consistency control expected energy function, and combining an MMC grid-connected system PCHD model to obtain an MMC grid-connected system closed loop state equation;
and S23, obtaining a passive consistency control law based on the PCHD model by combining an MMC grid-connected system closed loop state equation and an MMC grid-connected current state equation, and obtaining the controlled variable.
Further, Laplace matrix L of positive sequence subsystem and negative sequence subsystem of MMC grid-connected system1、L2The method specifically comprises the following steps:
Figure BDA0003141235510000041
wherein, Delta is L1、L2A is an adjacency matrix.
Further, the grid-connected current state variable error specifically includes:
Figure BDA0003141235510000042
Figure BDA0003141235510000043
Figure BDA0003141235510000044
wherein A isijWhen the subsystems have the same expected track, the alpha is 1; when the desired trajectories of the subsystems are different, α is 0.
Further, the PCHD model-based passive consistency control expected energy function is specifically:
Figure BDA0003141235510000045
further, the closed loop state equation of the MMC grid-connected system specifically includes:
Figure BDA0003141235510000046
further, the passive consistency control law based on the PCHD model is specifically:
Figure BDA0003141235510000047
Figure BDA0003141235510000051
Figure BDA0003141235510000052
Figure BDA0003141235510000053
Figure BDA0003141235510000054
Figure BDA0003141235510000055
Figure BDA0003141235510000056
Figure BDA0003141235510000057
wherein the content of the first and second substances,
Figure BDA0003141235510000058
the dq axis positive and negative sequence components of the AC side power supply voltage are respectively the obtained control quantity ra11、ra12、ra21、ra22Is a coefficient of a passive controller, A1、A2、B1、B2、C1、C2、D1、D2Positive sequence and negative sequence control variables, respectively.
Compared with the prior art, based on PCHD characteristics and passivity theory, the synchronization tracking of the grid-connected positive and negative sequence currents can be realized by introducing a consistency method, so that the synchronization effect is ensured; based on the established PCHD model of the MMC grid-connected system, the control target can obtain the minimum value at an expected balance point through energy function shaping, and the global gradual stability of the system can be effectively ensured by utilizing the input and output mapping of the PCHD system, so that the accuracy of obtaining the subsequent control quantity is ensured, and the synchronous stable tracking of the MMC grid-connected positive and negative sequence dual system is reliably realized;
in addition, the PCHD model-based MMC grid-connected system passive consistency controller can realize synchronous tracking of grid-connected current while ensuring the overall stability of the system, and has the advantages of simple control law form, small calculated amount, and better transient performance and stability.
Drawings
FIG. 1 is a schematic flow diagram of the process of the present invention;
FIG. 2 is a schematic process diagram of an embodiment of the method of the present invention;
FIG. 3 is a schematic diagram of a three-phase MMC circuit structure and its sub-module topology;
FIG. 4a is a schematic diagram of a positive sequence d-axis current waveform of the MMC in the embodiment;
FIG. 4b is a schematic diagram of a positive sequence q-axis current waveform of the MMC in the embodiment;
FIG. 4c is a schematic diagram of the negative sequence d-axis current waveform of the MMC in the embodiment;
FIG. 4d is a schematic diagram of the negative-sequence q-axis current waveform of the MMC in the embodiment.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
Examples
As shown in fig. 1, a passive consistency control method for a modular multilevel grid-connected current includes the following steps:
s1, establishing MMC grid-connected current under the condition of unbalanced grid voltage, and designing an expected global energy function of the MMC grid-connected system to obtain a PCHD model of the MMC grid-connected system under the condition of unbalanced grid voltage, wherein the method comprises the following specific steps:
s11, under the dq rotation coordinate system, defining the state variable as
Figure BDA0003141235510000061
Defining input variables as
Figure BDA0003141235510000062
Figure BDA0003141235510000063
Defining an output variable as
Figure BDA0003141235510000064
Wherein the positive sequence subsystem state variable is
Figure BDA0003141235510000065
Figure BDA0003141235510000066
Negative sequence subsystem state variables of
Figure BDA0003141235510000067
The positive sequence subsystem input variable is
Figure BDA0003141235510000068
Negative sequence subsystem input variables are
Figure BDA0003141235510000069
Figure BDA00031412355100000610
The positive sequence subsystem output variable is
Figure BDA00031412355100000611
The negative sequence subsystem output variable is
Figure BDA00031412355100000612
Wherein L iseqIs the inductance of the bridge arm,
Figure BDA00031412355100000613
respectively the dq axis positive and negative sequence components of the output voltage at the AC side,
Figure BDA00031412355100000614
are the dq axis positive and negative sequence components of the ac side supply current,
Figure BDA00031412355100000615
Figure BDA00031412355100000616
the dq axis positive and negative sequence components of the AC side power supply voltage are respectively;
s12, establishing a PCHD model-based MMC grid-connected current state equation based on the state variable, the input variable and the output variable in the step S11, designing an expected global energy function of the MMC grid-connected system, and obtaining the PCHD model of the MMC grid-connected system under the condition of unbalanced grid voltage, wherein the MMC grid-connected current state equation specifically comprises the following steps:
Figure BDA00031412355100000617
Figure BDA00031412355100000618
Figure BDA00031412355100000619
Figure BDA0003141235510000071
Figure BDA0003141235510000072
Figure BDA0003141235510000073
Figure BDA0003141235510000074
Figure BDA0003141235510000075
Figure BDA0003141235510000076
wherein J (x) is an interconnection matrix, R (x) is a damping matrix, g (x)) Is a port matrix, H (x) is an energy function, omega is a fundamental angular frequency, R is a bridge arm resistance,
Figure BDA0003141235510000077
is a differential operator;
the desired global energy function is specifically:
Figure BDA0003141235510000078
Figure BDA0003141235510000079
Figure BDA00031412355100000710
Figure BDA00031412355100000711
Figure BDA00031412355100000712
wherein x is*Is the desired trajectory for x and is,
Figure BDA00031412355100000713
respectively representing the dq axis expected positive sequence component and the negative sequence component of the alternating-current side power supply current, wherein D is a bridge arm inductance matrix;
the PCHD model of the MMC grid-connected system under the unbalanced power grid voltage specifically comprises the following steps:
Figure BDA00031412355100000714
Figure BDA00031412355100000715
Figure BDA00031412355100000716
wherein, Jd(x) Expect an interconnection matrix for the system, Rd(x) Desired damping matrix for the system, Ja(x)、Ra(x) Respectively an injected dissipation matrix and a damping matrix;
s2, constructing the PCHD model-based MMC grid-connected system PCHD model based on the step S1, and combining a consistency method to obtain a controlled variable, wherein the PCHD model-based MMC grid-connected passive consistency controller is based on the PCHD model under the condition of unbalanced grid voltage:
s21, setting Laplacian matrix L of positive sequence subsystem and negative sequence subsystem of MMC grid-connected system by combining consistency method1、L2：
Figure BDA0003141235510000081
Wherein, Delta is L1、L2A is an adjacency matrix;
s22, taking the difference between the state variable and the expected balance point as zero as a control target, and designing the error of the grid-connected current state variable as follows:
Figure BDA0003141235510000082
Figure BDA0003141235510000083
Figure BDA0003141235510000084
wherein A isijWhen the subsystems have the same expected track, the alpha is 1; when the expected trajectories of the subsystems are different, alpha is 0;
and then substituting the grid-connected current state variable error into a passive consistency control expected energy function based on the PCHD model:
Figure BDA0003141235510000085
and finally, combining with a PCHD model of the MMC grid-connected system to obtain a closed loop state equation of the MMC grid-connected system:
Figure BDA0003141235510000086
s23, combining an MMC grid-connected system closed loop state equation and an MMC grid-connected current state equation to obtain a passive consistency control law based on a PCHD model, namely obtaining a controlled variable, wherein the passive consistency control law based on the PCHD model specifically comprises the following steps:
Figure BDA0003141235510000091
Figure BDA0003141235510000092
Figure BDA0003141235510000093
Figure BDA0003141235510000094
Figure BDA0003141235510000095
Figure BDA0003141235510000096
Figure BDA0003141235510000097
Figure BDA0003141235510000098
wherein the content of the first and second substances,
Figure BDA0003141235510000099
the dq axis positive and negative sequence components of the AC side power supply voltage are respectively the obtained control quantity ra11、ra12、ra21、ra22Is a coefficient of a passive controller, A1、A2、B1、B2、C1、C2、D1、D2Respectively positive sequence control variable and negative sequence control variable;
s3, processing the control quantity by adopting a pulse modulation method to obtain a corresponding trigger pulse signal;
and S4, controlling the switching state of the converter of each phase bridge arm submodule of the MMC according to the trigger pulse signal.
The embodiment applies the above method, as shown in fig. 2, which includes the following steps:
step 1: the three-phase MMC circuit structure and the topological diagram of the sub-modules are shown in FIG. 3, and the MMC grid-connected current positive and negative sequence sub-system dynamic equations under dq rotation coordinate system obtained from FIG. 3 are respectively
Figure BDA00031412355100000910
Figure BDA00031412355100000911
Where ω is the fundamental angular frequency, LeqIs bridge arm inductance, R is bridge arm resistance,
Figure BDA0003141235510000101
respectively, an AC side output voltage urjThe dq-axis positive and negative sequence components of (j ═ a, b, c),
Figure BDA0003141235510000102
are respectively an AC side supply current ijThe dq-axis positive and negative sequence components of (j ═ a, b, c),
Figure BDA0003141235510000103
are respectively an AC side supply voltage ujThe dq-axis positive and negative sequence components of (j ═ a, b, c),
Figure BDA0003141235510000104
t is time, which is a differential operator.
Selecting a state variable x, an input variable u and an output variable y as follows:
Figure BDA0003141235510000105
wherein the content of the first and second substances,
Figure BDA0003141235510000106
Figure BDA0003141235510000107
Figure BDA0003141235510000108
designing an orthodefinite quadratic energy function H (x) as
Figure BDA0003141235510000109
Performing equivalent transformation on MMC grid-connected current positive and negative sequence subsystem dynamic equations (1) and (2) to obtain an MMC grid-connected current state equation as follows:
Figure BDA00031412355100001010
interconnection matrix
Figure BDA00031412355100001011
Damping matrix
Figure BDA00031412355100001012
Port matrix
Figure BDA00031412355100001013
In the formula (I), the compound is shown in the specification,
Figure BDA00031412355100001014
is a differential operator.
The design of the passivity MMC grid-connected system expected energy function based on the PCHD model specifically comprises the following steps:
Figure BDA00031412355100001015
Figure BDA00031412355100001016
and D is a bridge arm inductance matrix.
Introducing a state feedback control law
u1＝δ(x1) (7)
u2＝δ(x2) (8)
The PCHD model of the MMC grid-connected system under the voltage unbalance obtained by respectively substituting the formula (7) and the formula (8) into the formula (5) is concretely as follows:
Figure BDA0003141235510000111
in the formula, Jd(x)＝J(x)+Ja(x) Expect each other for the systemConnection matrix, satisfy
Figure BDA0003141235510000118
Rd(x)＝R(x)+Ra(x) Expect a damping matrix for the system, satisfy
Figure BDA0003141235510000119
Ja(x)、Ra(x) Respectively an injected dissipation matrix and a damping matrix.
The dissipation inequality can be derived from equations (4) and (9):
Figure BDA0003141235510000112
the left side of the equation (10) is increment of the whole MMC grid-connected current system, the right side is external supply energy, and the theory of passivity shows that: mapping u → x is strictly passive in output, and the MMC grid-connected current system has passive characteristics.
Step 2: setting Laplace matrix L of positive sequence subsystem and negative sequence subsystem of MMC grid-connected system by combining consistency method1、L2：
Figure BDA0003141235510000113
In the formula: l isijIs a matrix L1、L2The value of the node (i, j) is L1、L2A is an adjacency matrix.
And (3) designing a grid-connected current state variable error by taking the difference between the state variable and the expected balance point as zero as a control target:
Figure BDA0003141235510000114
in the formula (I), the compound is shown in the specification,
Figure BDA0003141235510000115
Figure BDA0003141235510000116
Figure BDA0003141235510000117
Figure BDA0003141235510000121
when the subsystems have the same desired trajectory, α is 1; when the desired trajectories of the subsystems are different, α is 0.
Substituting the formula (11) into the formula (6) to obtain the PCHD model-based passive consistency control expected energy function specifically as follows:
Figure BDA0003141235510000122
combining with a PCHD model of the MMC grid-connected system to obtain a closed-loop equation of the MMC grid-connected system, wherein the closed-loop equation is as follows:
Figure BDA0003141235510000123
wherein, Jd(x)＝J(x)+Ja(x) Interconnection matrix desired for the system, Rd(x)＝R(x)+Ra(x) Damping matrix desired for the system, Ja(x)、Ra(x) Respectively an injected dissipation matrix and a damping matrix.
The passive consistency control law based on the PCHD model can be obtained by combining the vertical type (5), the formula (12) and the formula (13):
Figure BDA0003141235510000124
Figure BDA0003141235510000125
in the formula (I), the compound is shown in the specification,
Figure BDA0003141235510000126
Figure BDA0003141235510000127
Figure BDA0003141235510000128
Figure BDA0003141235510000129
Figure BDA00031412355100001210
Figure BDA00031412355100001211
the equations (14) and (15) can ensure that the closed-loop control system can realize synchronous progressive tracking of the desired target of the MMC positive-sequence subsystem and the MMC negative-sequence subsystem on the premise of global progressive stabilization.
In this embodiment, a simulation model of an MMC capacitor voltage fluctuation control system is built in MATLAB/Simulink to verify the effectiveness of the present invention, and simulation parameters of this embodiment are shown in table 1.
TABLE 1
Simulation model parameter/unit Numerical value
Number of submodules n/ 36
Submodule capacitor C/mF 9
Bridge arm inductance L/mH 60
Bridge arm resistance R/omega 6
Rated voltage u at AC sidek/V 100
Frequency f/Hz of AC system 50
DC side voltage Udc/kV 180
AC side inductor Lg/mH 25.5
Rated active power P/MW 180
And carrying out simulation test by adopting an MMC grid-connected current passive consistency control method based on a PCHD model under the condition of unbalanced power grid voltage. When t is set to 0.2s, the ac side of the MMC has an a-phase grounding fault, and when t is set to 0.3s, the system recovers smoothly, and the MMC positive-sequence and negative-sequence d-axis and q-axis current simulation results are shown in fig. 4a to 4 d. FIG. 4a is a positive sequence d-axis current waveform; FIG. 4b is a positive sequence q-axis current waveform; FIG. 4c is a negative sequence d-axis current waveform; fig. 4d negative sequence q-axis current waveform. The analysis shows that the method can realize the rapid tracking of the expected positive sequence current track and the rapid inhibition of the negative sequence current under the conditions of power grid voltage balance and single-phase earth fault; by combining a consistency method, the adjustment time of the track tracking expected by the positive sequence current and the negative sequence current is about 6.8ms, the synchronous tracking of the positive sequence subsystem and the negative sequence subsystem is realized, and the tracking steady-state error is small.

Claims (10)

1. A passive consistency control method for modular multilevel grid-connected current is characterized by comprising the following steps:
s1, establishing MMC grid-connected current under the condition of unbalanced grid voltage, and designing an expected global energy function of the MMC grid-connected system to obtain a PCHD model of the MMC grid-connected system under the condition of unbalanced grid voltage;
s2, constructing a PCHD model-based MMC grid-connected system PCHD model based on the step S1, and combining a consistency method to obtain a controlled variable, wherein the PCHD model-based MMC grid-connected passive consistency controller is based on the PCHD model under the condition of unbalanced power grid voltage;
s3, processing the control quantity by adopting a pulse modulation method to obtain a corresponding trigger pulse signal;
and S4, controlling the switching state of the converter of each phase bridge arm submodule of the MMC according to the trigger pulse signal.
2. The passive consistency control method for the modular multilevel grid-connected current according to claim 1, wherein the step S1 specifically comprises the following steps:
s11, under the dq rotation coordinate system, defining the state variable as
Figure FDA0003141235500000011
Defining input variables as
Figure FDA0003141235500000012
Figure FDA0003141235500000013
Defining an output variable as
Figure FDA0003141235500000014
Wherein the positive sequence subsystem state variable is
Figure FDA0003141235500000015
Figure FDA0003141235500000016
Negative sequence subsystem state variables of
Figure FDA0003141235500000017
The positive sequence subsystem input variable is
Figure FDA0003141235500000018
Negative sequence subsystem input variables are
Figure FDA0003141235500000019
Figure FDA00031412355000000110
The positive sequence subsystem output variable is
Figure FDA00031412355000000111
The negative sequence subsystem output variable is
Figure FDA00031412355000000112
Wherein L iseqIs the inductance of the bridge arm,
Figure FDA00031412355000000113
respectively the dq axis positive and negative sequence components of the output voltage at the AC side,
Figure FDA00031412355000000114
are the dq axis positive and negative sequence components of the ac side supply current,
Figure FDA00031412355000000115
Figure FDA00031412355000000116
the dq axis positive and negative sequence components of the AC side power supply voltage are respectively;
s12, establishing an MMC grid-connected current state equation based on the PCHD model based on the state variable, the input variable and the output variable in the step S11, designing an expected global energy function of the MMC grid-connected system, and obtaining the PCHD model of the MMC grid-connected system under the condition of unbalanced power grid voltage.
3. The passive consistency control method for the modular multilevel grid-connected current according to claim 2, wherein the MMC grid-connected current state equation is specifically as follows:
Figure FDA0003141235500000021
Figure FDA0003141235500000022
Figure FDA0003141235500000023
Figure FDA0003141235500000024
Figure FDA0003141235500000025
Figure FDA0003141235500000026
Figure FDA0003141235500000027
Figure FDA0003141235500000028
Figure FDA0003141235500000029
wherein J (x) is an interconnection matrix, R (x) is a damping matrix, g (x) is a port matrix, H (x) is an energy function, omega is a fundamental angular frequency, R is a bridge arm resistance,
Figure FDA00031412355000000210
is a differential operator.
4. The passive consistency control method for the modular multilevel grid-connected current according to claim 3, wherein the expected global energy function is specifically as follows:
Figure FDA00031412355000000211
Figure FDA00031412355000000216
Figure FDA00031412355000000212
Figure FDA00031412355000000213
Figure FDA00031412355000000214
wherein x is*Is the desired trajectory for x and is,
Figure FDA00031412355000000215
respectively are the expected positive and negative sequence components of the dq axis of the alternating-current side power supply current, and D is a bridge arm inductance matrix.
5. The method according to claim 4, wherein the PCHD model of the MMC grid-connected system under the unbalanced grid voltage specifically comprises:
Figure FDA0003141235500000031
Jd(x)＝J(x)+Ja(x)，
Figure FDA0003141235500000032
Rd(x)＝R(x)+Ra(x)，
Figure FDA0003141235500000033
wherein, Jd(x) Expect an interconnection matrix for the system, Rd(x) Desired damping matrix for the system, Ja(x)、Ra(x) Respectively an injected dissipation matrix and a damping matrix.
6. The method according to claim 5, wherein the step S2 specifically comprises the following steps:
s21, setting Laplacian matrix L of positive sequence subsystem and negative sequence subsystem of MMC grid-connected system by combining consistency method1、L2；
S22, taking the difference between the state variable and the expected balance point as a control target, substituting the grid-connected current state variable error into a PCHD model-based passive consistency control expected energy function, and combining an MMC grid-connected system PCHD model to obtain an MMC grid-connected system closed loop state equation;
and S23, obtaining a passive consistency control law based on the PCHD model by combining an MMC grid-connected system closed loop state equation and an MMC grid-connected current state equation, and obtaining the controlled variable.
7. The method according to claim 6, wherein the Laplace matrix L of the MMC grid-connected system positive and negative sequence subsystems is a Laplace matrix L1、L2The method specifically comprises the following steps:
Figure FDA0003141235500000034
wherein, Delta is L1、L2A is an adjacency matrix.
8. The passive consistency control method for the modular multilevel grid-connected current according to claim 7, wherein the grid-connected current state variable error specifically comprises:
Figure FDA0003141235500000035
Figure FDA0003141235500000036
Figure FDA0003141235500000037
wherein A isijWhen the subsystems have the same expected track, the alpha is 1; when the desired trajectories of the subsystems are different, α is 0.
9. The method according to claim 8, wherein the PCHD model-based passive consistency control desired energy function is specifically:
Figure FDA0003141235500000041
the MMC grid-connected system closed loop state equation specifically comprises the following steps:
Figure FDA0003141235500000042
10. the method according to claim 9, wherein the PCHD model-based passive consistency control law specifically comprises:
Figure FDA0003141235500000043
Figure FDA0003141235500000044
Figure FDA0003141235500000045
Figure FDA0003141235500000046
Figure FDA0003141235500000047
Figure FDA0003141235500000048
Figure FDA0003141235500000049
Figure FDA00031412355000000410
wherein the content of the first and second substances,
Figure FDA00031412355000000411
the dq axis positive and negative sequence components of the AC side power supply voltage are respectively the obtained control quantity ra11、ra12、ra21、ra22Is a coefficient of a passive controller, A1、A2、B1、B2、C1、C2、D1、D2Positive sequence and negative sequence control variables, respectively.
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