CN113328645B - MMC control method for inhibiting voltage fluctuation of MMC capacitor - Google Patents

MMC control method for inhibiting voltage fluctuation of MMC capacitor Download PDF

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CN113328645B
CN113328645B CN202110572636.3A CN202110572636A CN113328645B CN 113328645 B CN113328645 B CN 113328645B CN 202110572636 A CN202110572636 A CN 202110572636A CN 113328645 B CN113328645 B CN 113328645B
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mmc
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CN113328645A (en
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薛花
王育飞
扈增辉
陈程
田广平
杨兴武
王�锋
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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
    • 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
    • H02M1/00—Details of apparatus for conversion
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H02M1/126—Arrangements for reducing harmonics from ac input or output using passive filters
    • 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

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Abstract

The invention relates to an MMC control method for inhibiting voltage fluctuation of an MMC capacitor, which comprises the following steps: the method is characterized in that the MMC capacitor voltage fluctuation suppression is taken as a target, and the linear transformation of the nonlinear mapping hyperplane between the MMC capacitor fluctuation voltage and the injection circulating current is realized through the mathematical relationship among smooth input variables, state variables, smooth output variables and finite-order time derivatives thereof; obtaining an injection circulation reference track by constructing a differential smooth control law and combining mathematical relations among smooth input variables, state variables, smooth output variables and finite-order time derivatives of the smooth input variables and the state variables; constructing a tracking control law of an injected circulation reference track based on a vector control method to obtain MMC control quantity; and controlling the working state of a switching tube in each submodule of the MMC according to the MMC control quantity. Compared with the prior art, the method can quickly and accurately obtain the injection circulation reference track under the condition that the MMC operates under the condition that the operating condition changes, so that the purpose of reliably and effectively inhibiting the voltage fluctuation of the MMC capacitor is achieved.

Description

MMC control method for inhibiting voltage fluctuation of MMC capacitor
Technical Field
The invention relates to the technical field of modular multilevel converter control, in particular to an MMC control method for inhibiting voltage fluctuation of an MMC capacitor.
Background
At present, many level of modularization converter (Modular multilevel converter, MMC) is by the wide application in distributed power source's the system of being incorporated into the power networks, MMC's mathematical model is simple, through switching on and shutting off of the switch tube in each submodule piece of control MMC, just can realize output voltage's switching, nevertheless because include a plurality of submodule pieces among the MMC, cut into along with cutting into of each submodule piece for capacitor voltage is difficult to reach complete equilibrium in the submodule piece, arouses MMC capacitor voltage easily and fluctuates.
In order to suppress the fluctuation of the capacitance voltage of the MMC, a circulation injection method is usually adopted, and traditionally, most of the methods utilize a table look-up method to generate an injection circulation reference track, the method is simple and quick, but when the system has external uncertainty interference or internal parameter perturbation, the circulation reference track cannot be timely and accurately given according to situation change due to the table look-up method, so that the suppression effect of the fluctuation of the capacitance voltage is deteriorated, and the engineering adaptability of the table look-up method is limited;
in addition, an analytical calculation method is used for accurately analyzing the nonlinear relation between the sub-module capacitor voltage and the injection circulating current so as to obtain the optimal injection circulating current value, but the nonlinear analysis method is complex, large in on-line calculation amount and difficult in engineering application.
Therefore, considering the influence of external uncertainty interference and unmodeled errors, under the condition of the smallest calculated amount, how to improve the analytic accuracy of the nonlinear relationship between the sub-module capacitor voltage and the injected circulating current is realized, which is the main contradiction and difficulty faced by the online calculation method of the injected circulating current reference track and is the key point for reliably and effectively inhibiting the fluctuation of the MMC capacitor voltage.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide an MMC control method for inhibiting the voltage fluctuation of an MMC capacitor, which can quickly and accurately obtain an injection circulation reference track under the condition of the variation of the operation condition of the MMC so as to realize the purpose of reliably and effectively inhibiting the voltage fluctuation of the MMC capacitor.
The purpose of the invention can be realized by the following technical scheme: an MMC control method for suppressing voltage fluctuation of an MMC capacitor comprises the following steps:
s1, aiming at suppressing the fluctuation of the MMC capacitor voltage, and realizing the linear transformation of a nonlinear mapping hyperplane between the MMC capacitor fluctuation voltage and an injection circulating current through the mathematical relationship among a smooth input variable, a state variable, a smooth output variable and a finite-order time derivative of the smooth input variable and the state variable;
s2, obtaining an injection circulation reference track by constructing a differential smooth control law and combining mathematical relations among smooth input variables, state variables, smooth output variables and finite-order time derivatives of the smooth input variables, the state variables and the smooth output variables;
s3, constructing a tracking control law of the injected circulation reference track based on a vector control method to obtain MMC control quantity;
and S4, controlling the working state of a switching tube in each submodule of the MMC according to the MMC control quantity.
Further, the smooth input variable in the step S1 is specifically a capacitance voltage of an upper bridge arm sub-module and a lower bridge arm sub-module of one phase of the MMC;
the state variables are MMC one-phase upper and lower bridge arm currents;
the smooth output variable is specifically capacitance voltage of the submodule of the upper bridge arm and the lower bridge arm of one phase of the MMC.
Further, the step S1 is specifically to obtain a mathematical relationship between the smooth input variable and the smooth output variable, and a mathematical relationship between the state variable and the smooth output variable and a finite-order time derivative thereof, respectively, based on a relationship between the currents of the upper and lower bridge arms and the capacitor voltages of the sub-modules of the upper and lower bridge arms.
Further, the relationship between the currents of the upper and lower bridge arms and the capacitor voltages of the sub-modules of the upper and lower bridge arms is specifically as follows:
Figure GDA0003776422610000021
u pa ＝N×u cpa
u na ＝N×u cna
wherein i pa 、i na Are respectively A-phase upper and lower bridge arm current u pa 、u na Respectively, the capacitor voltage of the sub-modules of the upper and lower bridge arms of phase A, the capacitor value of the sub-module C, and the capacitor value of the sub-module F mpa 、F mna Are the switching functions of the upper and lower bridge arms of phase A, u cpa 、u cna The capacitor voltages of single sub-modules of the upper bridge arm and the lower bridge arm of the phase A are respectively, and N is the number of the sub-modules of the upper bridge arm and the lower bridge arm.
Further, the mathematical relationship between the smoothed input variable and the smoothed output variable is:
γ 1 ＝u pa ＝μ 1
γ 2 ＝u na ＝μ 2
γ＝[γ 1 ,γ 2 ] T ＝[u pa ,u na ] T
μ＝[μ 1 ,μ 2 ] T ＝[u pa ,u na ] T
where γ is the smoothed input variable and μ is the smoothed output variable.
Further, the mathematical relationship between the state variable and the smoothed output variable and its finite-order time derivative is:
Figure GDA0003776422610000031
Figure GDA0003776422610000032
ξ＝[ξ 1 ,ξ 2 ] T ＝[i pa ,i na ] T
where ξ is the state variable.
Further, the step S2 specifically includes the following steps:
s21, setting the capacitor voltage reference value of the sub-module of the upper bridge arm and the lower bridge arm as mu * Constructing a differential smooth control law;
s22, according to a differential smooth control law, combining mathematical relations among a smooth input variable, a state variable, a smooth output variable and finite order time derivatives of the smooth input variable, the state variable and the smooth output variable to obtain a state variable expression, namely an upper bridge arm current equation and a lower bridge arm current equation;
and S23, according to the relation between the current of the upper and lower bridge arms and the circulation, combining the current equation of the upper and lower bridge arms in the step S22 to obtain an MMC each-phase injection circulation reference track.
Further, the differential smoothing control law specifically includes:
Figure GDA0003776422610000033
wherein, K 1 And K 2 Is a PI controller parameter.
Further, the current equations of the upper and lower bridge arms are specifically:
Figure GDA0003776422610000034
wherein, F mpa，mna Is F mpa Or F mna Specifically, the selection is based on the upper and lower bridge arms.
Further, the MMC injection circulation reference track specifically includes:
Figure GDA0003776422610000035
wherein, the first and the second end of the pipe are connected with each other,
Figure GDA0003776422610000036
for the injected circulating current reference trajectory, i, of the j-th phase in MMC pj 、i nj The j phase upper and lower bridge arm currents are respectively.
Compared with the prior art, the invention has the following advantages:
1. according to the invention, the currents of the upper and lower bridge arms are used as state variables, the capacitor voltages of the sub-modules of the upper and lower bridge arms are used as smooth output variables, and the mathematical relations among the smooth input variables, the state variables, the smooth output variables and finite-order time derivatives thereof are determined, so that the linear transformation of the nonlinear mapping hyperplane between the MMC capacitor fluctuation voltage and the injection circulation current can be realized, meanwhile, the optimal amplitude and phase angle of the injection circulation current can be rapidly and accurately obtained under the condition that the MMC operation condition changes, and the problem that a table look-up method is difficult to adapt to the MMC working condition change is solved.
2. The invention realizes that the hyperplane formed by the MMC capacitor fluctuation voltage and the injected circulating current is linear by determining the mathematical relationship among the smooth input variable, the state variable, the smooth output variable and the finite-order time derivative thereof, so that the subsequent reliable and accurate generation of the circulating current reference track can be realized only by a simple differential smooth control law, the defect of complex solving operation of the nonlinear relationship of an analytical calculation method is avoided, and the subsequent reliable and accurate acquisition of the MMC control quantity is also ensured, thereby realizing the purpose of reliably and effectively inhibiting the MMC capacitor voltage fluctuation under the condition of the MMC operation working condition change.
Drawings
FIG. 1 is a schematic flow diagram of the process of the present invention;
FIG. 2 is a schematic diagram of an injection circulation reference trajectory generation process in the embodiment;
FIG. 3 is a single phase equivalent circuit diagram of an MMC;
FIG. 4a is a desired trajectory and tracking waveform of a d-axis injection circulating current component of an MMC in an embodiment;
FIG. 4b is a q-axis injection circulating current component expected trace and tracking waveform of the MMC in the embodiment;
FIG. 4c is a waveform of capacitance voltage of the three-phase upper bridge arm submodule 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, an MMC control method for suppressing voltage fluctuation of an MMC capacitor includes the following steps:
s1, aiming at suppressing the fluctuation of MMC capacitor voltage, and realizing the linear transformation of a nonlinear mapping hyperplane between the MMC capacitor fluctuation voltage and an injected circulating current through the mathematical relation among a smooth input variable, a state variable, a smooth output variable and a finite order time derivative of the smooth input variable, wherein the smooth input variable is the capacitor voltage of an upper bridge arm submodule and a lower bridge arm submodule of one phase of the MMC;
the state variables are MMC one-phase upper and lower bridge arm currents;
the smooth output variable is specifically capacitance voltage of an MMC one-phase upper bridge arm submodule and a MMC one-phase lower bridge arm submodule;
specifically, based on the relationship between the currents of the upper and lower bridge arms and the capacitance voltages of the sub-modules of the upper and lower bridge arms:
Figure GDA0003776422610000051
u pa ＝N×u cpa
u na ＝N×u cna
in the formula i pa 、i na Are respectively A phase upper and lower bridge arm current u pa 、u na Respectively, the capacitor voltage of the sub-modules of the upper and lower bridge arms of phase A, the capacitance value of the sub-module C, and F mpa 、F mna Are the switching functions of the upper and lower bridge arms of phase A, u cpa 、u cna Respectively the capacitor voltage of single sub-modules of the upper bridge arm and the lower bridge arm of the phase A, and N is the number of the sub-modules of the upper bridge arm and the lower bridge arm;
and then respectively obtaining the mathematical relation between the smooth input variable and the smooth output variable:
γ 1 ＝u pa ＝μ 1
γ 2 ＝u na ＝μ 2
γ＝[γ 1 ,γ 2 ] T ＝[u pa ,u na ] T
μ＝[μ 1 ,μ 2 ] T ＝[u pa ,u na ] T
wherein gamma is a smooth input variable, and mu is a smooth output variable;
mathematical relationship of state variables to smoothed output variables and their finite-order time derivatives:
Figure GDA0003776422610000052
Figure GDA0003776422610000053
ξ＝[ξ 1 ,ξ 2 ] T ＝[i pa ,i na ] T
in the formula, xi is a state variable;
s2, obtaining an injection circulation reference track by constructing a differential smooth control law and combining mathematical relations among smooth input variables, state variables, smooth output variables and finite-order time derivatives thereof, wherein the specific is as follows:
s21, setting the reference value of the capacitor voltage of the sub-modules of the upper and lower bridge arms to be mu * And constructing a differential smooth control law:
Figure GDA0003776422610000054
wherein, K 1 And K 2 Is a PI controller parameter;
s22, according to a differential smooth control law, combining mathematical relations among smooth input variables, state variables, smooth output variables and finite order time derivatives thereof to obtain state variable expressions, namely upper and lower bridge arm current equations:
Figure GDA0003776422610000061
wherein, F mpa，mna Is F mpa Or F mna Specifically, the selection is carried out according to an upper bridge arm and a lower bridge arm;
s23, according to the relation between the current of the upper bridge arm and the current of the lower bridge arm and the circulation, combining the current equation of the upper bridge arm and the current equation of the lower bridge arm in the step S22 to obtain the circulation reference track of each phase of the MMC:
Figure GDA0003776422610000062
wherein the content of the first and second substances,
Figure GDA0003776422610000063
for the injected circulating current reference trajectory, i, of the j-th phase in MMC pj 、i nj The j phase upper and lower bridge arm currents are respectively;
s3, constructing a tracking control law of the injected circulation reference track based on a vector control method to obtain MMC control quantity;
and S4, controlling the working state of a switching tube in each submodule of the MMC according to the MMC control quantity.
The present embodiment applies the above technical solution, wherein a process of generating an injection circulation reference trajectory is shown in fig. 2:
1. the method is characterized in that the MMC capacitor voltage fluctuation suppression is taken as a target, and the linear transformation of the nonlinear mapping hyperplane between the MMC capacitor fluctuation voltage and the injection circulating current is realized through the mutual achievement of the relations among smooth input, state variables, smooth output variables and finite-order time derivatives thereof;
2. and a simple differential smooth control law is designed, so that the injected circulating current reference track can be quickly and accurately solved, and conditions are provided for suppressing the voltage fluctuation of the MMC capacitor.
Specifically, firstly, the MMC sub-module capacitor voltage gamma = [ gamma ] of the upper and lower bridge arm of one phase is selected 1 ,γ 2 ] T ＝[u pa ,u na ] T For smooth input variables, upper and lower bridge arm current xi = [ xi = 1 ,ξ 2 ] T ＝[i pa ,i na ] T As a state variable, the capacitor voltage mu of the upper and lower bridge arm sub-modules is = [ mu ] 1 ,μ 2 ] T ＝[u pa ,u na ] T To smooth the output variables.
According to the single-phase equivalent circuit diagram of the modular multilevel converter shown in fig. 3, it can be known that the currents of the upper and lower bridge arms and the capacitor voltages of the sub-modules of the upper and lower bridge arms satisfy:
Figure GDA0003776422610000064
in the formula: c is the sub-module capacitance, F mpa 、F mna Are respectively the switching functions of the upper and lower bridge arms of the A phase u cpa 、u cna The capacitor voltages of the single sub-modules of the upper bridge arm and the lower bridge arm of the phase A respectively meet the following conditions:
u pa ＝N×u cpa
u na ＝N×u cna
in the formula: and N is the number of the upper bridge arm submodule and the lower bridge arm submodule.
From equation (1), the smoothed input variable, the state variable, can be represented by the smoothed output variable as:
Figure GDA0003776422610000071
the analysis of the formula (2) shows that the state variable and the smooth input variable can be represented by a smooth output variable and a time derivative of a finite order thereof, and then according to a differential smoothing theory, a nonlinear system described by a smooth input variable gamma, a state variable xi and a smooth output variable mu is a smooth system, so that the linear transformation of a nonlinear mapping hyperplane between the MMC capacitor fluctuation voltage and the injection circulating current can be realized, and a simple differential smoothing control law is designed, so that the rapid calculation of the state variable reference track can be realized.
Then setting the reference value of the capacitor voltage of the sub-modules of the upper and lower bridge arms as mu * The differential smoothing control law is designed as follows:
Figure GDA0003776422610000072
in the formula: k 1 And K 2 Are controller parameters.
Substituting the formula (3) into the formula (2) to obtain a state variable expression, namely the upper and lower bridge arm current equations are:
Figure GDA0003776422610000073
in the formula: f mpa，mna Is F mpa Or F mna And selecting according to the upper bridge arm and the lower bridge arm.
The relation between the current of the upper and lower bridge arms and the circulation is combined with the formula (4) to obtain the circulation reference track of each phase of the MMC
Figure GDA0003776422610000074
Comprises the following steps:
Figure GDA0003776422610000075
in the formula: i.e. i pj 、i nj The j phase upper and lower bridge arm currents are respectively.
Injecting MMC phases into a circulating current reference track
Figure GDA0003776422610000076
The method is used for tracking a circulating current reference track by vector control, and the suppression of the capacitance voltage fluctuation of the MMC sub-module is realized.
In this embodiment, an MMC and a simulation model for generating an injection circulation reference track for suppressing the fluctuation of the capacitance voltage are built in MATLAB/Simulink, and the effectiveness of the generation of the injection circulation reference track is verified, and the simulation parameters of this embodiment are shown in table 1.
TABLE 1
Figure GDA0003776422610000077
Figure GDA0003776422610000081
Under the steady-state operation of the MMC system, a simulation test is carried out by adopting an injection circulating current reference track generation method based on differential smooth control, the injection circulating current reference track generation method and a vector control method for inhibiting the capacitance voltage fluctuation are started when t =0.5s, the step of the resistance and the inductance of the a-phase bridge arm are increased by 50%, and the simulation result is shown in figures 4 a-4 c.
As can be seen from the analysis of fig. 4a to 4b, the injected circulating current expected trajectory can be accurately generated by using the differential smoothing control method, the injected circulating current is mainly based on the double-frequency circulating current component and also contains a small amount of quadruple-frequency circulating current components, and the result is consistent with the analysis result of the nonlinear mapping relationship between the MMC capacitor fluctuation voltage and the injected circulating current obtained by using the numerical calculation method, thereby verifying the accuracy of obtaining the injected circulating current expected trajectory by using the differential smoothing control method; when the MMC parameters are perturbed, the method still has quick response and keeps better dynamic and static characteristics. Fig. 4c shows that, by applying the proposed injection circulation reference trajectory generation method and the vector control method, the voltage fluctuation of the MMC capacitor is rapidly reduced, the effectiveness of the proposed injection circulation reference trajectory generation method is verified, and the voltage fluctuation of the MMC capacitor can be reliably and effectively suppressed. The method provided by the invention can overcome the defect that the traditional table look-up method is only suitable for steady-state operation conditions under MMC rated parameters when the injected circulation reference track is accurately obtained, solves the problems that the analytical calculation method is complex in calculation and difficult to apply in engineering, has simple operation of a differential smooth control law, and can automatically adjust the generation of the injected circulation reference track according to the variation of the MMC operation condition, thereby ensuring that the fluctuation of the MMC capacitance voltage can be effectively inhibited under the condition of variation of the MMC operation condition.

Claims (4)

1. An MMC control method for suppressing MMC capacitor voltage fluctuation is characterized by comprising the following steps of:
s1, aiming at suppressing the fluctuation of the MMC capacitor voltage, and realizing the linear transformation of a nonlinear mapping hyperplane between the MMC capacitor fluctuation voltage and an injection circulating current through the mathematical relationship among a smooth input variable, a state variable, a smooth output variable and a finite-order time derivative of the smooth input variable and the state variable;
s2, obtaining an injection circulation reference track by constructing a differential smooth control law and combining mathematical relations among smooth input variables, state variables, smooth output variables and finite-order time derivatives of the smooth input variables, the state variables and the smooth output variables;
s3, constructing a tracking control law of the injected circulation reference track based on a vector control method to obtain MMC controlled quantity;
s4, controlling the working state of a switching tube in each submodule of the MMC according to the MMC control quantity;
the smooth input variable in the step S1 is MMC one-phase upper and lower bridge arm submodule capacitor voltage;
the state variables are MMC one-phase upper and lower bridge arm currents;
the smooth output variable is MMC sub-module capacitance voltage of an upper bridge arm and a lower bridge arm of one phase;
the step S1 is specifically based on the relationship between the current of the upper bridge arm and the current of the lower bridge arm and the capacitor voltage of the sub-modules of the upper bridge arm and the lower bridge arm, so as to respectively obtain the mathematical relationship between a smooth input variable and a smooth output variable and the mathematical relationship between a state variable and the smooth output variable and the finite-order time derivative thereof;
the relationship between the currents of the upper and lower bridge arms and the capacitor voltages of the sub-modules of the upper and lower bridge arms is as follows:
Figure FDA0003776422600000011
u pa ＝N×u cpa
u na ＝N×u cna
wherein i pa 、i na Are respectively A-phase upper and lower bridge arm current u pa 、u na Respectively, the capacitor voltage of the sub-modules of the upper and lower bridge arms of phase A, the capacitor value of the sub-module C, and the capacitor value of the sub-module F mpa 、F mna Are the switching functions of the upper and lower bridge arms of phase A, u cpa 、u cna Respectively the capacitor voltage of single sub-modules of the upper bridge arm and the lower bridge arm of the phase A, and N is the number of the sub-modules of the upper bridge arm and the lower bridge arm;
the mathematical relationship between the smoothed input variable and the smoothed output variable is:
γ 1 ＝u pa ＝μ 1
γ 2 ＝u na ＝μ 2
γ＝[γ 1 ,γ 2 ] T ＝[u pa ,u na ] T
μ＝[μ 1 ,μ 2 ] T ＝[u pa ,u na ] T
wherein, gamma is a smooth input variable, and mu is a smooth output variable;
the mathematical relationship between the state variable and the smoothed output variable and its finite order time derivative is:
Figure FDA0003776422600000021
Figure FDA0003776422600000022
ξ＝[ξ 1 ,ξ 2 ] T ＝[i pa ,i na ] T
wherein xi is a state variable;
the step S2 specifically includes the following steps:
s21, setting the reference value of the capacitor voltage of the sub-modules of the upper and lower bridge arms to be mu * Constructing a differential smooth control law;
s22, according to a differential smooth control law, combining mathematical relations among a smooth input variable, a state variable, a smooth output variable and a finite order time derivative of the smooth output variable to obtain a state variable expression, namely an upper bridge arm current equation and a lower bridge arm current equation;
and S23, according to the relation between the current of the upper and lower bridge arms and the circulation, combining the current equation of the upper and lower bridge arms in the step S22 to obtain an MMC each-phase injection circulation reference track.
2. The MMC control method for suppressing MMC capacitor voltage fluctuation of claim 1, wherein the differential smoothing control law is specifically:
Figure FDA0003776422600000023
wherein, K 1 And K 2 Is a PI controller parameter.
3. The MMC control method for suppressing MMC capacitor voltage fluctuation according to claim 2, characterized in that, the upper and lower bridge arm current equations specifically are:
Figure FDA0003776422600000024
wherein, F mpa，mna Is F mpa Or F mna Specifically, the selection is based on the upper and lower bridge arms.
4. The MMC control method for suppressing MMC capacitor voltage fluctuation according to claim 3, characterized in that, each phase of the MMC injects a circulating current reference trace specifically as follows:
Figure FDA0003776422600000025
wherein, the first and the second end of the pipe are connected with each other,
Figure FDA0003776422600000026
injection circulating current reference track i of j phase in MMC pj 、i nj The j phase upper and lower bridge arm currents are respectively.
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CN111740429A (en) * 2020-06-22 2020-10-02 上海电力大学 Passivity sliding mode control method for MMC-UPQC under power grid voltage unbalance condition
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