CN112039106B - Method for restraining DC voltage fluctuation based on MMC virtual capacitor - Google Patents

Method for restraining DC voltage fluctuation based on MMC virtual capacitor Download PDF

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CN112039106B
CN112039106B CN202010710072.0A CN202010710072A CN112039106B CN 112039106 B CN112039106 B CN 112039106B CN 202010710072 A CN202010710072 A CN 202010710072A CN 112039106 B CN112039106 B CN 112039106B
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CN112039106A (en
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李清
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Maintenance and Test Center of Extra High Voltage Power Transmission Co
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    • 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
    • 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
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • 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
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H02J2003/365—Reducing harmonics or oscillations in HVDC
    • 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]

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Abstract

The invention discloses a method for inhibiting DC voltage fluctuation based on MMC virtual capacitors, which is characterized in that electrical parameters of an MMC are controlled through a preset control strategy, the control strategy is equivalent to a virtual capacitor with adjustable capacitance, and the virtual coefficient of the virtual capacitor is adjusted according to the amplitude of voltage fluctuation so as to inhibit the DC voltage fluctuation. The invention has the beneficial effects that: by presetting the control strategy in the MMC, the converter and the virtual capacitor can be made to show a physical behavior similar to that of a converter with a capacitor with adjustable size connected in parallel with a dc supply network, and the virtual capacitor represents the behavior of the MMC after the control strategy provided by the invention. Specifically, the virtual coefficient is adjusted to change the size of the virtual capacitor, so that the inertia of the direct-current power supply network is influenced, the capability of the direct-current power supply network for inhibiting voltage fluctuation can be enhanced, and the stability of the direct-current power supply network is improved.

Description

Method for restraining DC voltage fluctuation based on MMC virtual capacitor
Technical Field
The invention relates to the technical field of flexible direct current transmission, in particular to a method for inhibiting DC voltage fluctuation based on an MMC virtual capacitor.
Background
A modular multilevel converter (modular multilevel converter MMC) is a converter topology commonly used in a flexible direct current transmission system. The converter commonly used in the high-voltage direct-current transmission project at present is a VSC, the converter comprises a large capacitor connected with a DC power grid, the inertia of the DC power grid depends on the size of the capacitor connected with the DC power grid, if a large capacitor is connected with the DC power grid, the DC power grid has higher inertia, conversely, if the connected capacitor is smaller, the inertia of the DC power grid is smaller, but the voltage of the capacitor end is coupled with the voltage of the DC power transmission network, which is a prominent disadvantage, besides, the output signal of the VSC is different from the ideal signal greatly, and the ideal signal can be obtained through multiple filtering.
For dc systems, the dynamic variation of the dc voltage depends on the amount of energy stored in the system capacitor, and according to the relevant literature, for a typical MMC system, it is able to maintain the dc voltage constant for only 40ms after voltage fluctuations occur, which is quite detrimental to the operation of the system. In the prior art, part of MMC control strategies are not based on energy, when a voltage difference is generated between a bridge arm voltage of a converter and a direct-current power supply network, a DC power supply network automatically adjusts power to reduce the voltage difference, and power exchange between a capacitor in the bridge arm and the DC power supply network is based on the change of the bridge arm capacitance tracking DC power supply network voltage, so that no additional control component is needed, and because no corresponding control component exists, part of variables in this type of MMC are not controlled, which results in the loss of converter robustness. In addition, some of the MMC control strategies in the prior art are based on energy MMC control, which can control the internal energy of the MMC by temporarily applying a mismatch between dc power and ac power, however, this type of converter is disadvantageous for decoupling the sub-module terminal voltage from the dc supply network voltage and cannot effectively suppress the voltage fluctuations of the dc supply network.
In summary, the conventional converter and the control method thereof cannot effectively manage the internal energy of the MMC, and cannot provide a stable suppression effect on the voltage fluctuation of the dc power supply network by using the energy.
Disclosure of Invention
Aiming at the problems, the invention provides a method for inhibiting DC voltage fluctuation based on an MMC virtual capacitor, which can convert direct current quantity into alternating current quantity or convert alternating current quantity into direct current quantity. The method mainly solves the problem that the existing MMC control strategy cannot provide stable inhibition effect on the voltage fluctuation of a direct current power supply network.
In order to solve the technical problems, the technical scheme of the invention is as follows:
the method comprises the steps of controlling electrical parameters of the MMC through a preset control strategy, enabling the control strategy to be equivalent to a virtual capacitor with adjustable capacitance, and adjusting a virtual coefficient of the virtual capacitor according to the amplitude of voltage fluctuation so as to suppress the DC voltage fluctuation.
The suppression system based on the MMC virtual capacitor to the DC voltage fluctuation is further provided, the electrical parameters of the MMC are controlled through a preset control system, the control system is equivalent to a virtual capacitor with the adjustable capacitance, and the virtual coefficient of the virtual capacitor is adjusted according to the voltage fluctuation amplitude. The control system comprises an energy reference value calculation module, an internal energy control module, a direct current voltage control module, a PI control module, a sliding mode direct power control module and a current control module; the energy reference value calculation module is used for calculating the MMC's internal energy reference value, internal energy control module is used for calculating virtual capacitance's absorbed power reference value, direct current voltage control module is used for calculating alternating current power's reference value, PI control module is used for calculating the first intermediate current volume reference quantity relevant with direct current power, the direct power control module of slipform is used for calculating the second intermediate current volume reference value relevant with alternating current power, current control module is used for calculating intermediate current variable.
A computer-readable storage medium is also proposed, which stores a computer program, wherein the computer program causes a computer to execute the method of the above-mentioned suppression method.
The invention has the beneficial effects that: by presetting the control strategy in the MMC, the converter and the virtual capacitor can be made to show a physical behavior similar to that of a converter with a capacitor with adjustable size connected in parallel with a dc supply network, and the virtual capacitor represents the behavior of the MMC after the control strategy provided by the invention. Specifically, the virtual coefficient is adjusted to change the size of the virtual capacitor, so that the inertia of the direct-current power supply network is influenced, the capability of the direct-current power supply network for inhibiting voltage fluctuation can be enhanced, and the stability of the direct-current power supply network is improved.
Drawings
FIG. 1 is a flow chart of a disclosed suppression method according to an embodiment of the present invention;
FIG. 2 is a main control block diagram of a suppression system according to a second embodiment of the present invention;
FIG. 3 is a DC voltage control diagram of a suppression method according to an embodiment of the present invention;
FIG. 4 is a power flow diagram of a suppression method according to an embodiment of the present invention;
fig. 5 is an equivalent circuit of the suppression method according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer and clearer, the following detailed description of the present invention is provided with reference to the accompanying drawings and detailed description. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some but not all of the relevant aspects of the present invention are shown in the drawings.
Example one
According to fig. 1, the embodiment provides a method for suppressing DC voltage fluctuation based on a virtual capacitor of an MMC, wherein an electrical parameter of the MMC is controlled through a preset control strategy, the control strategy is equivalent to a virtual capacitor with adjustable capacitance, and a virtual coefficient of the virtual capacitor is adjusted according to the amplitude of voltage fluctuation to suppress DC voltage fluctuation.
The control strategy comprises the following steps:
step one, defining a point where a converter is connected with a direct current power supply network as a common connection point, taking a square value of a voltage actual value of the common connection point, a square value of a voltage nominal value of the common connection point, an MMC internal energy nominal value and a virtual inertia coefficient with adjustable size as input, and outputting an MMC internal energy reference value, wherein the calculation method comprises the following steps:
Figure GDA0003296812590000031
wherein the content of the first and second substances,
Figure GDA0003296812590000032
reference value for MMC internal energy, CtotTo concentrate the capacitance value of the capacitor, vdcIs the actual value of the voltage of the point of common connection, vdc0Is a voltage reference value of the common connection point,
Figure GDA0003296812590000033
is the nominal value of the MMC internal energy, kVIIs the virtual inertia coefficient.
Step two, the MMC internal energy reference value and the MMC internal energy actual value are used as input, wherein an energy tracking part can be realized by any controller, so that w∑Following
Figure GDA0003296812590000034
In a variation of (1) are
Figure GDA0003296812590000035
The basic method can be realized by using a PI controller, and for calculating the absorbed power reference value of the virtual capacitor, the calculation method is as follows:
Figure GDA0003296812590000036
wherein, w∑Is the actual value of internal energy, CeqThe capacitance of the polymer capacitor is Ceq＝6Ctot，
Figure GDA0003296812590000037
A reference value of power is absorbed for the virtual capacitance.
Step three, as shown in fig. 3, taking a square value of the actual voltage value of the common connection point and a square value of the reference voltage value of the common connection point as input, and outputting a reference value of the ac power, wherein the calculation method is as follows:
Figure GDA0003296812590000038
wherein the content of the first and second substances,
Figure GDA0003296812590000039
is a reference value of AC power, Fv(s) is a PI controller, and the PI controller is a power amplifier,
Figure GDA00032968125900000310
which is the voltage reference of the common connection point, s refers to the frequency domain,
Figure GDA00032968125900000311
C∑an equivalent capacitance of a DC circuit having C∑＝Cdc+CVI，wnFor natural frequency, it is usually taken
Figure GDA00032968125900000312
And TrFor ideal response time, ζ is 0.707 as damping ratio.
Step four, as shown in fig. 4, inputting a difference between the reference value of the dc power and the actual value of the dc power, and outputting a first reference amount of intermediate current related to the dc power, wherein the calculation method comprises the following steps:
reference value of DC power
Figure GDA0003296812590000041
Actual value of DC power Pdc＝vdcidiffi
Figure GDA0003296812590000042
Wherein h (v) is a PI controller,
Figure GDA0003296812590000043
the reference value and the actual value of the common-mode component of the bridge arm current are respectively.
Figure GDA0003296812590000044
Kpv，pdcProportional coefficient of PI controller, Kiv，pdcIs the PI controller integration coefficient.
Step five, taking the difference value between the alternating current power reference value and the alternating current power actual value and the difference value between the alternating current reactive power reference value and the alternating current reactive power actual value as input, and outputting a second intermediate current amount reference value related to the alternating current power, wherein the calculation method comprises the following steps:
Pac＝vgdigd
Figure GDA0003296812590000045
Figure GDA0003296812590000046
Figure GDA0003296812590000047
Figure GDA0003296812590000048
wherein, PacIs the actual value of the AC power, vgdIs the direct component of the AC voltage, igdIs the direct-axis component of the alternating current, e is the difference between the actual alternating power and the reference value,
Figure GDA0003296812590000049
the derivative of the respective quantity with respect to time is indicated,
Figure GDA00032968125900000410
for reference values of the direct component of the alternating current, sign being a sign function, Kpv、KivTo solve separately
Figure GDA00032968125900000411
The proportional and integral constants involved are,
Figure GDA00032968125900000412
Figure GDA00032968125900000413
both indicate the derivation of the content in brackets,
Figure GDA00032968125900000414
Qacrespectively an ac reactive power reference value and an actual value,
Figure GDA00032968125900000415
presentation pair
Figure GDA00032968125900000416
Integration is performed. Ki，qacTo solve for
Figure GDA00032968125900000417
The integration constants involved.
Step six, inputting the first intermediate current quantity reference quantity and the second intermediate current variable, and outputting an intermediate current variable, wherein the calculation method comprises the following steps:
Figure GDA00032968125900000418
Figure GDA0003296812590000051
Figure GDA0003296812590000052
Figure GDA0003296812590000053
Figure GDA0003296812590000054
Figure GDA0003296812590000055
Figure GDA0003296812590000056
wherein the content of the first and second substances,
Figure GDA0003296812590000057
is composed of
Figure GDA0003296812590000058
Reference values of the direct axis and quadrature axis components after park transformation, q represents the quadrature axis, d represents the direct axis,
Figure GDA0003296812590000059
is a reference value for the differential mode component of the bridge arm voltage,
Figure GDA00032968125900000510
igqreference and actual values, v, of quadrature-axis components of the alternating current, respectivelygqFor the quadrature component of the AC voltage, p (v) is a PI controller, LarmIs bridge arm inductance, LfThe inductance on the ac side, w is the angular velocity,
Figure GDA00032968125900000519
is the common modulus of the bridge arm voltages,
Figure GDA00032968125900000511
is the equivalent voltage of the upper bridge arm,
Figure GDA00032968125900000512
is the equivalent voltage of the lower bridge arm,
Figure GDA00032968125900000513
and
Figure GDA00032968125900000514
the voltage values of the upper bridge arm and the lower bridge arm centralized capacitors are respectively,
Figure GDA00032968125900000515
and
Figure GDA00032968125900000516
is the duty ratio of the upper bridge arm and the lower bridge arm,
Figure GDA00032968125900000517
for an AC phase voltage, RfIs an AC side resistor, RarmIs a resistance of a bridge arm, and is,
Figure GDA00032968125900000518
is an alternating phase current.
In general, the reference values are denoted with a prime and the actual values are denoted without a prime.
As shown in FIG. 5, it can be observed that there is an adjustable capacitance CVIVirtual capacitor C ofVIIn parallel with the dc supply network (for convenience of presentation, C)VIRepresenting both the physical actual capacitor and the magnitude of the capacitance of that capacitor). Wherein "virtual" is used to indicate that the capacitor is not a real physical capacitor present in the converter, the present invention can make the converter and the virtual capacitor show a physical behavior similar to that of a converter with a capacitor with adjustable size connected in parallel with a dc supply network by presetting a control strategy in the MMC, and the virtual capacitor shows the behavior of the MMC after the control strategy provided by the present invention. Specifically, the virtual coefficient is adjusted to change the size of the virtual capacitor, so that the inertia of the direct-current power supply network is influenced, the capability of the direct-current power supply network for inhibiting voltage fluctuation can be enhanced, and the stability of the direct-current power supply network is improved.
Example two
The utility model provides an inhibition system to DC voltage fluctuation based on virtual electric capacity of MMC, controls MMC's electrical parameter through predetermined control system, will control system equivalence is a virtual condenser of electric capacity size adjustable, according to voltage fluctuation's range adjustment virtual condenser's virtual coefficient.
As shown in fig. 2, the control system includes an energy reference value calculation module, an internal energy control module, a dc voltage control module, a PI control module, a sliding mode direct power control module, and a current control module;
the energy reference value calculation module is used for calculating the MMC's internal energy reference value, internal energy control module is used for calculating virtual capacitance's absorbed power reference value, direct current voltage control module is used for calculating alternating current power's reference value, PI control module is used for calculating the first intermediate current volume reference quantity relevant with direct current power, the direct power control module of slipform is used for calculating the second intermediate current volume reference value relevant with alternating current power, current control module is used for calculating intermediate current variable.
The calculation methods of the six modules are respectively implemented corresponding to the steps from one to six in the first embodiment.
EXAMPLE III
A computer-readable storage medium storing a computer program, wherein the computer program causes a computer to perform the method of embodiment one.
The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention accordingly, and not to limit the protection scope of the present invention accordingly. All equivalent changes or modifications made in accordance with the spirit of the present disclosure are intended to be covered by the scope of the present disclosure.

Claims (3)

1. A method for restraining DC voltage fluctuation based on MMC virtual capacitance is characterized in that electrical parameters of an MMC are controlled through a preset control strategy, the control strategy is equivalent to a virtual capacitor with adjustable capacitance, and a virtual coefficient of the virtual capacitor is adjusted according to the amplitude of voltage fluctuation so as to restrain the DC voltage fluctuation;
the control strategy comprises the steps of defining a point where a converter is connected with a direct current power supply network as a common connection point, taking a square value of a voltage actual value of the common connection point, a square value of a voltage nominal value of the common connection point, an MMC internal energy nominal value and a virtual inertia coefficient with adjustable size as input, and outputting an MMC internal energy reference value, wherein the calculation method comprises the following steps:
Figure FDA0003296812580000011
wherein the content of the first and second substances,
Figure FDA0003296812580000012
reference value for MMC internal energy, CtotTo concentrate the capacitance value of the capacitor, vdcIs the actual value of the voltage of the point of common connection, vdc0Is the nominal value of the voltage at the point of common connection,
Figure FDA0003296812580000013
is the nominal value of the MMC internal energy, kVIIs a virtual inertia coefficient;
the control strategy also comprises that the MMC internal energy reference value and the MMC internal energy actual value are used as input, and the energy tracking part is controlled by the PI controller to control w∑Following
Figure FDA0003296812580000014
In a variation of (1) are
Figure FDA0003296812580000015
For calculating the absorbed power reference value of the virtual capacitor, the calculation method is as follows:
Figure FDA0003296812580000016
wherein, w∑Is the actual value of internal energy, CeqThe capacitance of the polymer capacitor is Ceq＝6Ctot，
Figure FDA0003296812580000017
A reference value for the absorbed power of the virtual capacitance;
the control strategy also comprises the following steps of taking a square value of the actual voltage value of the public connection point and a square value of the reference voltage value of the public connection point as input, and outputting a reference value of alternating current power, wherein the calculation method comprises the following steps:
Figure FDA0003296812580000018
wherein the content of the first and second substances,
Figure FDA0003296812580000019
is a reference value of AC power, Fv(s) is a PI controller, and the PI controller is a power amplifier,
Figure FDA00032968125800000110
a voltage reference value for the common connection point;
the control strategy also comprises the steps of inputting a difference value between a direct current power reference value and a direct current power actual value, and outputting a first intermediate current amount reference quantity related to the direct current power, wherein the calculation method comprises the following steps:
reference value of DC power
Figure FDA00032968125800000111
Actual value of DC power Pdc＝vdcidiffi
Figure FDA00032968125800000112
Wherein h (v) is a PI controller,
Figure FDA00032968125800000113
idiffirespectively taking a reference value and an actual value of the common-mode component of the bridge arm current;
the control strategy also comprises the following steps of taking the difference value between the AC active power reference value and the AC active power actual value and the difference value between the AC reactive power reference value and the AC reactive power actual value as input, and outputting a second intermediate current amount reference value related to the AC power, wherein the calculation method comprises the following steps:
Pac＝vgdigd
Figure FDA0003296812580000021
Figure FDA0003296812580000022
Figure FDA0003296812580000023
Figure FDA0003296812580000024
wherein, PacIs the actual value of the AC power, vgdIs the direct component of the AC voltage, igdIs the direct-axis component of the alternating current, e is the difference between the actual alternating power and the reference value,
Figure FDA0003296812580000025
the derivative of the respective quantity with respect to time is indicated,
Figure FDA0003296812580000026
for reference values of the direct component of the alternating current, sign being a sign function, Kpv、KivTo solve separately
Figure FDA0003296812580000027
The proportional and integral constants involved are,
Figure FDA0003296812580000028
Figure FDA0003296812580000029
both indicate the derivation of the content in brackets,
Figure FDA00032968125800000210
Qacrespectively an ac reactive power reference value and an actual value,
Figure FDA00032968125800000211
presentation pair
Figure FDA00032968125800000212
Performing integration;
the control strategy also comprises the steps of inputting the first intermediate current quantity reference quantity and the second intermediate current variable and outputting an intermediate current variable, wherein the calculation method comprises the following steps:
Figure FDA00032968125800000213
Figure FDA00032968125800000214
Figure FDA00032968125800000215
Figure FDA00032968125800000216
Figure FDA00032968125800000217
Figure FDA00032968125800000218
Figure FDA0003296812580000031
wherein the content of the first and second substances,
Figure FDA0003296812580000032
is composed of
Figure FDA0003296812580000033
Reference values of the direct axis and quadrature axis components after park transformation, q represents the quadrature axis, d represents the direct axis,
Figure FDA0003296812580000034
is a reference value for the differential mode component of the bridge arm voltage,
Figure FDA0003296812580000035
igqreference and actual values, v, of quadrature-axis components of the alternating current, respectivelygqFor the quadrature component of the AC voltage, p (v) is a PI controller, LarmIs bridge arm inductance, LfThe inductance on the ac side, w is the angular velocity,
Figure FDA0003296812580000036
is the common modulus of the bridge arm voltages,
Figure FDA0003296812580000037
is the equivalent voltage of the upper bridge arm,
Figure FDA0003296812580000038
is the equivalent voltage of the lower bridge arm,
Figure FDA0003296812580000039
and
Figure FDA00032968125800000310
the voltage values of the upper bridge arm and the lower bridge arm centralized capacitors are respectively,
Figure FDA00032968125800000311
and
Figure FDA00032968125800000312
is the duty ratio of the upper bridge arm and the lower bridge arm,
Figure FDA00032968125800000313
for an AC phase voltage, RfIs an AC side resistor, RarmIs a resistance of a bridge arm, and is,
Figure FDA00032968125800000314
is an alternating phase current.
2. A suppression system for DC voltage fluctuation based on MMC virtual capacitance is characterized in that electrical parameters of an MMC are controlled through a preset control system, the control system is equivalent to a virtual capacitor with adjustable capacitance, and a virtual coefficient of the virtual capacitor is adjusted according to the amplitude of voltage fluctuation;
the control system comprises an energy reference value calculation module, an internal energy control module, a direct current voltage control module, a PI control module, a sliding mode direct power control module and a current control module;
the energy reference value calculation module is used for calculating the internal energy reference value of the MMC, and comprises the following steps of defining a point where a converter is connected with a direct-current power supply network as a common connection point, and outputting the MMC internal energy reference value by taking a square value of a voltage actual value of the common connection point, a square value of a voltage nominal value of the common connection point, a MMC internal energy nominal value and a virtual inertia coefficient with adjustable size as input, wherein the point is used as the common connection point, and the calculation method comprises the following steps:
Figure FDA00032968125800000315
wherein the content of the first and second substances,
Figure FDA00032968125800000316
reference value for MMC internal energy, CtotTo concentrate the capacitance value of the capacitor, vdcIs the actual value of the voltage of the point of common connection, vdc0Is the nominal value of the voltage at the point of common connection,
Figure FDA00032968125800000317
is the nominal value of the MMC internal energy, kVIIs a virtual inertia coefficient;
the internal energy control module is used for calculating the absorbed power reference value of the virtual capacitor, and comprises the MMC internal energy reference value and the MMC internal energy actual value as input, and the energy tracking part is controlled by the PI controller to control w∑Following
Figure FDA00032968125800000318
In a variation of (1) are
Figure FDA00032968125800000319
For calculating the absorbed power reference value of the virtual capacitor, the calculation method is as follows:
Figure FDA0003296812580000041
wherein, w∑Is the actual value of internal energy, CeqThe capacitance of the polymer capacitor is Ceq＝6Ctot，
Figure FDA0003296812580000042
A reference value for the absorbed power of the virtual capacitance;
the direct current voltage control module is used for calculating a reference value of alternating current power, and comprises the following steps of taking a square value of a voltage actual value of the public connection point and a square value of a voltage reference value of the public connection point as input, and outputting the reference value of the alternating current power, wherein the calculation method comprises the following steps:
Figure FDA0003296812580000043
wherein the content of the first and second substances,
Figure FDA0003296812580000044
is a reference value of AC power, Fv(s) is a PI controller, and the PI controller is a power amplifier,
Figure FDA0003296812580000045
a voltage reference value for the common connection point;
the PI control module is used for calculating a first intermediate current amount reference quantity related to the direct current power, and comprises the following steps of inputting a difference value between a direct current power reference value and a direct current power actual value, and outputting the first intermediate current amount reference quantity related to the direct current power, wherein the calculation method comprises the following steps:
reference value of DC power
Figure FDA0003296812580000046
Actual value of DC power Pdc＝vdcidiffi
Figure FDA0003296812580000047
Wherein h (v) is a PI controller,
Figure FDA0003296812580000048
idiffirespectively taking a reference value and an actual value of the common-mode component of the bridge arm current;
the sliding mode direct power control module is used for calculating a second intermediate current magnitude reference value related to alternating current power, and comprises the following steps of taking a difference value between the alternating current active power reference value and an alternating current active power actual value, and a difference value between an alternating current reactive power reference value and an alternating current reactive power actual value as input, and outputting the second intermediate current magnitude reference value related to the alternating current power, wherein the calculation method comprises the following steps:
Pac＝vgdigd
Figure FDA0003296812580000049
Figure FDA00032968125800000410
Figure FDA00032968125800000411
Figure FDA00032968125800000412
wherein, PacIs the actual value of the AC power, vgdIs the direct component of the AC voltage, igdIs the direct-axis component of the alternating current, e is the difference between the actual alternating power and the reference value,
Figure FDA0003296812580000051
the derivative of the respective quantity with respect to time is indicated,
Figure FDA0003296812580000052
for reference values of the direct component of the alternating current, sign being a sign function, Kpv、KivTo solve separately
Figure FDA0003296812580000053
The proportional and integral constants involved are,
Figure FDA0003296812580000054
Figure FDA0003296812580000055
both indicate the derivation of the content in brackets,
Figure FDA0003296812580000056
Qacrespectively an ac reactive power reference value and an actual value,
Figure FDA0003296812580000057
presentation pair
Figure FDA0003296812580000058
Performing integration;
the current control module is used for calculating an intermediate current variable, and comprises the following steps of inputting the first intermediate current reference quantity and the second intermediate current variable, and outputting the intermediate current variable:
Figure FDA0003296812580000059
Figure FDA00032968125800000510
Figure FDA00032968125800000511
Figure FDA00032968125800000512
Figure FDA00032968125800000513
Figure FDA00032968125800000514
Figure FDA00032968125800000515
wherein the content of the first and second substances,
Figure FDA00032968125800000516
is composed of
Figure FDA00032968125800000517
Reference values of the direct axis and quadrature axis components after park transformation, q represents the quadrature axis, d represents the direct axis,
Figure FDA00032968125800000518
is a reference value for the differential mode component of the bridge arm voltage,
Figure FDA00032968125800000519
igqreference and actual values, v, of quadrature-axis components of the alternating current, respectivelygqFor the quadrature component of the AC voltage, p (v) is a PI controller, LarmIs bridge arm inductance, LfThe inductance on the ac side, w is the angular velocity,
Figure FDA00032968125800000520
is the common modulus of the bridge arm voltages,
Figure FDA00032968125800000521
is the equivalent voltage of the upper bridge arm,
Figure FDA00032968125800000522
is the equivalent voltage of the lower bridge arm,
Figure FDA00032968125800000523
and
Figure FDA00032968125800000529
the voltage values of the upper bridge arm and the lower bridge arm centralized capacitors are respectively,
Figure FDA00032968125800000525
and
Figure FDA00032968125800000526
is the duty ratio of the upper bridge arm and the lower bridge arm,
Figure FDA00032968125800000527
for an AC phase voltage, RfIs an AC side resistor, RarmIs a resistance of a bridge arm, and is,
Figure FDA00032968125800000528
is an alternating phase current.
3. A computer-readable storage medium, characterized in that the computer-readable storage medium stores a computer program, wherein the computer program causes a computer to perform the method of claim 1.
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