CN112134472A - Double-end system direct current side resonance control method and system based on MMC current converter - Google Patents

Double-end system direct current side resonance control method and system based on MMC current converter Download PDF

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CN112134472A
CN112134472A CN202010856159.9A CN202010856159A CN112134472A CN 112134472 A CN112134472 A CN 112134472A CN 202010856159 A CN202010856159 A CN 202010856159A CN 112134472 A CN112134472 A CN 112134472A
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mmc
bridge arm
current
current side
direct current
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高明
王小红
侯凯
梁帅奇
吴林平
邹宁
牟晓春
马炜程
闫冬
张青杰
储厚成
陈永龙
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Nari Technology Co Ltd
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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
    • 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
    • H02M1/14—Arrangements for reducing ripples from dc input or output
    • 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
    • H02M7/003—Constructional details, e.g. physical layout, assembly, wiring or busbar connections
    • 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 double-end system direct current side resonance control method and a double-end system direct current side resonance control system based on an MMC converter, wherein the method comprises the following steps: obtaining a direct current side current reference value according to the given active power and the direct current side voltage given value when the system operates; obtaining a current deviation value according to the actual value of the direct current side current and the reference value of the direct current side current; the current deviation value passes through a PI controller to obtain a common mode voltage component; subtracting the common-mode voltage component from the original MMC bridge arm modulation signal to obtain a modified MMC bridge arm modulation signal; and determining the number of MMC sub-modules actually put into the MMC converter by combining a recent level approximation modulation strategy based on the corrected MMC bridge arm modulation signals, and finishing the direct-current side resonance control of the double-end system based on the MMC converter. According to the invention, only two signals of active power and direct-current side voltage of the system need to be acquired, and damping is indirectly injected into the system by adjusting the number of the MMC sub-modules in real time, so that the aim of inhibiting direct-current side resonance is achieved.

Description

Double-end system direct current side resonance control method and system based on MMC current converter
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a double-end system direct-current side resonance control method and system based on an MMC current converter.
Background
With the wide use of electric energy, the requirements on the capacity and the switching frequency of the converter are higher and higher. Modular Multilevel Converters (MMC) have been widely used in the field of flexible dc power transmission as a Modular design, scalable Voltage Source Converter (VSC), and the field of forward ac/dc hybrid power distribution networks has been expanded. As shown in fig. 1, the pseudo-bipolar connection mode is a typical topology of an ac/dc hybrid power distribution network, and a positive-negative symmetric loop is formed by grounding a midpoint of a dc side capacitor, which is beneficial to reducing the insulation level of a line.
The modular multilevel converter comprises a plurality of MMC sub-modules, and on one hand, because the MMC sub-modules have a floating capacitor, a bridge arm resistor and a bridge arm reactance, and a double-end system has a direct-current side filter inductor, the double-end system based on the MMC converter presents a second-order underdamping characteristic and is easy to generate resonance. On the other hand, most of the existing modular multilevel converters adopt a nearest level approximation modulation strategy, the number of input submodules is determined according to the rated voltage and the modulation voltage of the submodules, a submodule voltage-sharing control strategy and a submodule capacitor sequencing result, and finally the finally input submodules are determined according to the bridge arm current direction. Although the capacitor voltage sequencing strategy can reduce the calculated amount and reduce the switching frequency and the switching loss, the capacitor voltage difference and the direct current bus current fluctuation of different sub-modules are easy to cause resonance. The direct current bus fluctuation problem caused by the two angles can cause overcurrent and overvoltage of the IGBT module, loss of the MMC converter, system resonance and threat to system operation.
FIG. 2 is a topological diagram of a three-phase MMC, and it can be known from FIG. 2 that an upper bridge arm and a lower bridge arm are symmetrically distributed and comprise n power units UjkAnd bridge arm inductance L0In series (j is the number of phases and k is the power cell number). Bridge arm inductance L0The connection point is an AC output end, a power unit UjkThe number N of switches depends on the voltage class and the power switch selected. Bridge arm inductance L0The function is to suppress the circulation current and the current rise rate in case of sub-module failure. VT1And VT2Is IGBT, VD1And VD2Is a diode, C0Is a sub-module DC side capacitor, UcRepresenting the sub-module capacitance voltage usmFor sub-module voltage, ismTo flow sub-module current. The operation mode is determined according to the switching state and the current direction of the IGBT as shown in FIG. 3, and the operation state is shown in Table 1.
Watch 1
Figure BDA0002646462750000011
In order to inhibit the direct current side bus fluctuation, researchers around the harmonic damping control of the direct current side of the MMC converter are developed by experts of domestic and foreign scholars at present. The harmonic suppression strategy is further developed by Zhongjun et al of the institute of Electrical Power science of Beijing Sifang Zhi Bao Automation GmbH and Chongqing electric Power company in the text "method for suppressing harmonic suppression on the DC side of the Flexible direct System based on damping controlThe results of line theory analysis and simulation verification show that the direct current side resonance suppression strategy based on damping injection can effectively reduce direct current side current fluctuation and converter loss. The basic principle is as follows: by injecting damping into the system, a damping voltage U is calculated in the systemdcr，UdcrEqual to, opposite to the value of the excitation voltage source causing the resonance, i.e.:
Udcr＝kIdch (1)
in the above formula: i isdchIs a harmonic component of the direct current side current.
In addition, the voltage U is modulatedMMCAt damping voltage UdcrThe adjustment under the action is as follows:
Figure BDA0002646462750000021
in the above formula:
Figure BDA0002646462750000022
modulating the voltage, ± u, for the upper and lower bridge armsacnModulating the voltage value u for the AC side generated in the system voltage outer loop controller2ndThe voltage component caused by the double frequency conversion of the bridge arm.
The DC side resonance damping control block diagram is shown in FIG. 4, LF is a low frequency filter, KPWMFor the transfer function, U, of the converterdc1And Udc2Is a voltage on both sides of the DC side, Udc1And Udc2The actual direct current is obtained by calculation. The harmonic component of the direct current can be effectively extracted by the equation (1) through connecting an equivalent damping resistor k in series to the system impedance branch and subtracting the actual value of the direct current from the value after the LF filtering.
Although the damping control strategy can reduce the resonance probability and the converter loss, the following disadvantages exist:
(1) the damping resistor k also causes loss when the system operates;
(2) the damping control-based direct current side resonance suppression strategy needs to additionally configure a low-pass filter, calculate a converter transfer function, collect direct current side voltage, bridge arm modulation voltage, system alternating current side modulation voltage, voltage causing double frequency circulation components and other signals, and a control system is complex in calculation, more in collected signals and inconvenient for engineering realization;
(3) after the damping injection strategy, the control strategy has a good suppression effect on the harmonic waves of the low frequency band, but the suppression effect on the resonance of the high frequency band is obviously reduced.
Disclosure of Invention
Aiming at the problems, the invention provides a method and a system for controlling direct current side resonance of a double-end system based on an MMC converter, which only need to acquire two signals of active power and direct current side voltage of the system, indirectly inject damping into the system through adjusting the number of MMC sub-modules in real time, and reduce direct current side resonance.
In order to achieve the technical purpose and achieve the technical effects, the invention is realized by the following technical scheme:
in a first aspect, the present invention provides a method for controlling a dc-side resonance of a dual-terminal system based on an MMC converter, including:
obtaining a direct current side current reference value according to the given active power and the direct current side voltage given value when the system operates;
obtaining a current deviation value according to the actual value of the direct current side current and the direct current side current reference value;
obtaining a common-mode voltage component by the current deviation value through a PI controller;
subtracting the common-mode voltage component from the original MMC bridge arm modulation signal to obtain a modified MMC bridge arm modulation signal;
and determining the number of MMC sub-modules actually input in the MMC converter by combining a recent level approximation modulation strategy based on the corrected MMC bridge arm modulation signal, and finishing the direct-current side resonance control of the double-end system based on the MMC converter.
Optionally, the common mode voltage component UcomThe calculation formula of (A) is as follows:
Figure BDA0002646462750000031
in the formula, RdTo an equivalent virtual resistance, Δ IdIs a current deviation, IdcrefFor a given value of the direct-current side current, IdcIs the actual value of the direct current, P*For a given active power at which the system is operating,
Figure BDA0002646462750000032
the voltage on the direct current side is given.
Optionally, after completing double-end system dc side resonance control based on the MMC converter, the MMC converter k phase voltage mathematical model is:
Figure BDA0002646462750000033
in the formula of UdiIs a DC side voltage, L0Is equivalent inductance of bridge arm, R0Is equivalent resistance of bridge arm, idiffkFor bridge arm current, UkIs total voltage of k-phase bridge arm, UcomIs a common mode voltage component.
Optionally, the method for obtaining the original MMC bridge arm modulation signal includes: and obtaining a bridge arm voltage signal by using a PI controller under a synchronous rotating coordinate system, and obtaining an original modulation signal of the MMC bridge arm based on the bridge arm voltage signal and a recent level approximation modulation strategy.
Optionally, the method for obtaining the original MMC bridge arm modulation signal includes:
converting abc three-phase alternating current quantity of the MMC current converter into dq coordinates through dq decoupling coordinate transformation;
setting the given values of d-axis and q-axis currents
Figure BDA0002646462750000034
Respectively with the actual value Id、IqThe difference signal of (2) is passed through a PI controller;
combining coupling components of dq axes
Figure BDA0002646462750000035
And dq axis component u of three-phase voltage at alternating current side of MMC convertercd、ucqThe modulation signals are jointly determined.
In a second aspect, the present invention provides a double-ended system dc-side resonance control system based on an MMC converter, including:
the direct current side current reference value calculating unit is used for solving a direct current side current reference value according to the given active power and the given direct current side voltage value when the system operates;
the current deviation value calculation unit is used for solving a current deviation value according to a direct current side current actual value and the direct current side current reference value;
the common-mode voltage component acquisition unit is used for obtaining a common-mode voltage component by passing the current deviation value through a PI controller;
the corrected MMC bridge arm modulation signal calculation unit is used for subtracting the common-mode voltage component from the original MMC bridge arm modulation signal to obtain a corrected MMC bridge arm modulation signal;
and the MMC submodule input quantity determining unit is used for determining the quantity of the MMC submodules actually input into the MMC converter by combining a recent level approximation modulation strategy based on the corrected MMC bridge arm modulation signals, and finishing double-end system direct-current side resonance control based on the MMC converter.
Optionally, the common mode voltage component UcomThe calculation formula of (A) is as follows:
Figure BDA0002646462750000041
in the formula, RdTo an equivalent virtual resistance, Δ IdIs a current deviation, IdcrefFor a given value of the direct-current side current, IdcIs the actual value of the direct current, P*For a given active power at which the system is operating,
Figure BDA0002646462750000045
the voltage on the direct current side is given.
Optionally, after completing double-end system dc side resonance control based on the MMC converter, the MMC converter k phase voltage mathematical model is:
Figure BDA0002646462750000042
in the formula of UdiIs a DC side voltage, L0Is equivalent inductance of bridge arm, R0Is equivalent resistance of bridge arm, idiffkFor bridge arm current, UkIs total voltage of k-phase bridge arm, UcomIs a common mode voltage component.
Optionally, the method for obtaining the original MMC bridge arm modulation signal includes: and obtaining a bridge arm voltage signal by using a PI controller under a synchronous rotating coordinate system, and obtaining an original modulation signal of the MMC bridge arm based on the bridge arm voltage signal and a recent level approximation modulation strategy.
Optionally, the method for obtaining the original MMC bridge arm modulation signal includes:
converting abc three-phase alternating current quantity of the MMC current converter into dq coordinates through dq decoupling coordinate transformation;
setting the given values of d-axis and q-axis currents
Figure BDA0002646462750000043
Respectively with the actual value Id、IqThe difference signal of (2) is passed through a PI controller;
combining coupling components of dq axes
Figure BDA0002646462750000044
And dq axis component u of three-phase voltage at alternating current side of MMC convertercd、ucqThe modulation signals are jointly determined.
Compared with the prior art, the invention has the beneficial effects that:
the invention indirectly realizes the function of the damping resistor k by adjusting the number of the input submodules in real time, and avoids the loss of the damping resistor k for system injection.
The invention does not need to additionally design a low-pass filter, calculate the transfer function of the converter and reduce the acquisition information required by control.
Drawings
In order that the present disclosure may be more readily and clearly understood, reference is now made to the following detailed description of the present disclosure taken in conjunction with the accompanying drawings, in which:
fig. 1 is a topological diagram of a typical ac/dc hybrid power distribution network in the prior art;
FIG. 2 is a prior art three-phase MMC inverter topology;
FIG. 3 is a schematic diagram illustrating an MMC sub-module in the prior art;
FIG. 4 is a block diagram of a DC side resonance damping control strategy in the prior art;
FIG. 5(a) is an MMC converter DC side n-th harmonic equivalent circuit;
FIG. 5(b) is a unipolar equivalent circuit of the MMC converter;
FIG. 6 is a schematic block diagram of a double-end system DC-side resonance control method based on an MMC converter in the present invention;
FIG. 7(a) is a simulation result diagram of PSCAD without DC side resonance suppression;
FIG. 7(b) is a diagram showing simulation results of PSCAD with DC-side resonance suppression;
FIG. 7(c) is a PSCAD simulation result diagram of the non-DC side resonance suppression local current;
FIG. 7(d) is a PSCAD simulation result diagram of the local current with DC side resonance suppression;
FIG. 7(e) is a simulation effect diagram of tracking the given value PSCAD by the actual value of the current of the DC suppression strategy;
FIG. 8(a) is a diagram of a DC-side-free resonance suppression RTDS semi-physical simulation result;
FIG. 8(b) is a diagram of DC-side resonance suppression RTDS semi-physical simulation results.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of the invention.
The following detailed description of the principles of the invention is provided in connection with the accompanying drawings.
Example 1
The k-phase voltage mathematical model of the MMC converter is shown in formula (3) and is used for describing the relation among the MMC single-phase bridge arm current, the direct-current side voltage, the upper bridge arm current, the lower bridge arm current and the bridge arm circulating current.
Figure BDA0002646462750000061
Wherein L is0Is bridge arm inductance, R0Is bridge arm resistance idiffkFor bridge arm current, UkIs total voltage of k-phase bridge arm, Uk＝Upk+Unk，UpkIs the k-phase upper bridge arm voltage, UnkIs the voltage of the lower bridge arm of the k phase,
Figure BDA0002646462750000062
Idiis a direct side current, icirckIs a bridge arm circulating current.
Therefore, the direct-current side harmonic wave expression is shown in formula (4) and is used for describing the relationship between the three-phase equivalent circuit on the direct-current side of the MMC and the voltage on the direct-current side.
Figure BDA0002646462750000063
In the formula of Udi(n) is the direct current side nth harmonic voltage, Idi(n) n harmonic currents on the DC side, C the equivalent capacitance of the bridge arm, L0Is equivalent inductance of bridge arm, R0Is equivalent resistance of a bridge arm.
When the number of the input MMC sub-modules is N, the capacitance number of the MMC converter is 2N, and the capacitance voltage C of the sub-modules is assumed0Equivalent capacitance on DC side of MMC converter
Figure BDA0002646462750000064
Equivalent resistance R2R0Equivalent inductance L2L0DC line equivalent inductor Ld. Therefore, three phases of the direct-current side MMC current converter are connected in parallel and then are connected with the direct-current filter inductor in series, and N MMC sub-module capacitors C are arranged in the group0Are connected in series. The MMC direct-current side nth harmonic equivalent circuit is shown in fig. 5(a), and the unipolar equivalent circuit is shown in fig. 5 (b).
In order to fully exert the advantages of the MMC converter in multiple control dimensions and combine the idea of damping injection, the total voltage U of each phase of bridge arm is measuredk(Uk＝Upk+Unk) As the controlled variable, utilize the bias current of direct current side electric current set value and actual value to pass through PI controller, dynamic adjustment MMC puts into submodule figure, realizes direct current resonance and suppresses, so equation (3) can be revised as:
Figure BDA0002646462750000065
in the formula (5), the reaction mixture is,
Figure BDA0002646462750000066
ΔId＝Idcref-Idc，Ucom＝ΔIdRd，Rdto an equivalent virtual resistance, Δ IdFor current deviation, UdiIs a DC side voltage, L0Is equivalent inductance of bridge arm, R0Is equivalent resistance of bridge arm, idiffkFor bridge arm current, UjkFor k-phase bridge arm voltage, UcomIs a common mode voltage component.
Common mode voltage component UcomThe calculation formula of (A) is as follows:
Figure BDA0002646462750000071
in the formula, RdTo an equivalent virtual resistance, Δ IdIs a current deviation, IdcrefFor a given value of the direct-current side current, IdcIs the actual value of the direct current, P*Given the active power for the system to operate,
Figure BDA0002646462750000072
the voltage on the direct current side is given.
Therefore, an embodiment of the present invention provides a method for controlling dc-side resonance of a dual-terminal system based on an MMC converter, as shown in fig. 5, including the following steps:
(1) obtaining a direct current side current reference value according to the given active power and the direct current side voltage given value when the system operates;
(2) obtaining a current deviation value according to the actual value of the direct current side current and the direct current side current reference value;
(3) obtaining a common-mode voltage component by the current deviation value through a PI controller;
(4, subtracting the common-mode voltage component from the original MMC bridge arm modulation signal to obtain a modified MMC bridge arm modulation signal;
(5) and determining the number of sub-modules actually input into the MMC converter by combining a recent level approximation modulation strategy based on the modified MMC bridge arm modulation signal, and completing the direct current side resonance control of the double-end system based on the MMC converter, wherein the specific process of determining the number of the MMC sub-modules actually input into the MMC converter by combining the recent level approximation modulation strategy based on the modified MMC bridge arm modulation signal can be realized by the prior art, and redundant description is not given in the invention.
After completing double-end system direct current side resonance control based on the MMC transverter, the MMC transverter k phase voltage mathematical model is:
Figure BDA0002646462750000073
in the formula (I), the compound is shown in the specification,
Figure BDA0002646462750000074
ΔId＝Idcref-Idc，Ucom＝ΔIdRd，Rdto an equivalent virtual resistance, Δ IdFor current deviation, in the formula, UdiIs a DC side voltage, L0Is equivalent inductance of bridge arm, R0Is equivalent resistance of bridge arm, idiffkFor bridge arm current, UjkFor k-phase bridge arm voltage, UcomIs a common mode voltage component.
Common mode voltage component UcomThe calculation formula of (A) is as follows:
Figure BDA0002646462750000075
in the formula, RdTo an equivalent virtual resistance, Δ IdIs a current deviation, IdcrefFor a given value of the direct-current side current, IdcIs the actual value of the direct current, P*Given the active power for the system to operate,
Figure BDA0002646462750000084
the voltage on the direct current side is given.
Obtaining the deviation delta I of the direct current according to the given value and the actual value of the direct currentdObtaining a common mode voltage component U by using a PI controllercom，UcomAnd subtracting the original bridge arm modulation signal to obtain a bridge arm actual modulation signal to determine the input quantity of the MMC sub-modules, so that the suppression of the direct current side current resonance is realized.
The method for acquiring the original MMC bridge arm modulation signal comprises the following steps:
converting abc three-phase alternating current quantity of the MMC current converter into dq coordinates through dq decoupling coordinate transformation;
setting the given values of d-axis and q-axis currents
Figure BDA0002646462750000081
Respectively with the actual value Id、IqThe difference signal of (2) is passed through a PI controller;
combining coupling components of dq axes
Figure BDA0002646462750000083
And dq axis component u of three-phase voltage at alternating current side of MMC convertercd、ucqThe modulation signals are jointly determined.
And (3) building a simulation model on PSCAD simulation software and an RTDS semi-physical simulation platform by combining the direct-current side resonance suppression control block diagram shown in FIG. 6. The specific parameters are as follows: the system capacity is 10MVA, the positive voltage of the direct current side is 10kV, the negative voltage of the direct current side is-10 kV, the system transmits active power of 10MW, the two ends of the system are connected to an active power grid, the MMC1 of the rectification side is used for determining active power control, and the MMC2 of the inversion side is used for determining direct current voltage control.
The PSCAD simulation result graph during steady-state operation of the system is shown in fig. 7, where fig. 7(a) shows no dc-side resonance suppression, fig. 7(b) shows no dc-side resonance suppression, fig. 7(c) shows no dc-side resonance suppression local current graph, fig. 7(d) shows a dc-side resonance suppression local current graph, and fig. 7(e) shows a dc suppression strategy current actual value tracking given value effect graph; the RTDS semi-physical simulation result diagram is shown in fig. 8, where fig. 8(a) shows no dc-side resonance suppression and fig. 8(b) shows dc-side resonance suppression.
According to PSCAD and RTDS simulation results, when the system operates in a steady state, the strategy provided by the invention can effectively inhibit current fluctuation caused by direct current side resonance of the double-end system based on the MMC current converter, and compared with the traditional resonance inhibition strategy, the strategy has the advantages that:
the method has the advantages that a low-pass filter does not need to be additionally designed, the transfer function of the current converter is calculated, and the acquisition information needed by control is reduced.
Secondly, the number of the input sub-modules is adjusted in real time, so that the effect of the damping resistor k is indirectly realized, and the loss of the damping resistor k for system injection is avoided.
Example 2
The k-phase voltage mathematical model of the MMC converter is shown in formula (3) and is used for describing the relation among the MMC single-phase bridge arm current, the direct-current side voltage, the upper bridge arm current, the lower bridge arm current and the bridge arm circulating current.
Figure BDA0002646462750000082
Wherein L is0Is bridge arm inductance, R0Is bridge arm resistance idiffkFor bridge arm current, UkIs the total voltage of the k-phase bridge arm,
Uk＝Upk+Unk，Upkis the k-phase upper bridge arm voltage, UnkIs the voltage of the lower bridge arm of the k phase,
Figure BDA0002646462750000091
Idiis a direct side current, icirckIs a bridge arm circulating current.
Therefore, the direct-current side harmonic wave expression is shown in formula (4) and is used for describing the relationship between the three-phase equivalent circuit on the direct-current side of the MMC and the voltage on the direct-current side.
Figure BDA0002646462750000092
In the formula of Udi(n) is the direct current side nth harmonic voltage, Idi(n) n harmonic currents on the DC side, C the equivalent capacitance of the bridge arm, L0Is equivalent inductance of bridge arm, R0Is equivalent resistance of a bridge arm.
When the number of the input MMC sub-modules is N, the capacitance number of the MMC converter is 2N, and the capacitance voltage C of the sub-modules is assumed0Equivalent capacitance on DC side of MMC converter
Figure BDA0002646462750000093
Equivalent resistance R2R0Equivalent inductance L2L0DC line equivalent inductor Ld. Therefore, three phases of the direct-current side MMC current converter are connected in parallel and then are connected with the direct-current filter inductor in series, and N MMC sub-module capacitors C are arranged in the group0Are connected in series. The MMC direct-current side nth harmonic equivalent circuit is shown in fig. 5(a), and the unipolar equivalent circuit is shown in fig. 5 (b).
In order to fully exert the advantages of the MMC converter in multiple control dimensions and combine the idea of damping injection, the total voltage U of each phase of bridge arm is measuredk(Uk＝Upk+Unk) As a control amount, in the formula (3) UkComponent-added common mode voltage component UcomTo obtain Uk' the MMC input sub-module number is dynamically adjusted to realize direct current resonance suppression, so the formula (3) can be modified as follows:
Figure BDA0002646462750000094
in the formula (5), the reaction mixture is,
Figure BDA0002646462750000095
ΔId＝Idcref-Idc，Ucom＝ΔIdRd. Wherein R isdTo an equivalent virtual resistance, Δ IdFor current deviation, UdiIs a DC side voltage, L0Is equivalent inductance of bridge arm, R0Is equivalent resistance of bridge arm, idiffkFor bridge arm current, UjkFor k-phase bridge arm voltage, UcomIs a common mode voltage component.
Common mode voltage component UcomThe calculation formula of (A) is as follows:
Figure BDA0002646462750000096
in the formula, RdTo an equivalent virtual resistance, Δ IdIs a current deviation, IdcrefFor a given value of the direct-current side current, IdcIs the actual value of the direct current, P*Given the active power for the system to operate,
Figure BDA0002646462750000101
the voltage on the direct current side is given.
Based on the same inventive concept as embodiment 1, an embodiment of the present invention provides a dual-terminal system dc side resonance control system based on an MMC converter, including:
the direct current side current reference value calculating unit is used for solving a direct current side current reference value according to the given active power and the given direct current side voltage value when the system operates;
the current deviation value calculation unit is used for solving a current deviation value according to a direct current side current actual value and the direct current side current reference value;
the common-mode voltage component acquisition unit is used for obtaining a common-mode voltage component by passing the current deviation value through a PI controller;
the corrected MMC bridge arm modulation signal calculation unit is used for subtracting the common-mode voltage component from the original MMC bridge arm modulation signal to obtain a corrected MMC bridge arm modulation signal;
and the MMC submodule input quantity determining unit is used for determining the quantity of the MMC submodules actually input into the MMC converter by combining a recent level approximation modulation strategy based on the corrected MMC bridge arm modulation signals, and finishing double-end system direct-current side resonance control based on the MMC converter.
After completing double-end system direct current side resonance control based on the MMC transverter, the MMC transverter k phase voltage mathematical model is:
Figure BDA0002646462750000102
in the formula (I), the compound is shown in the specification,
Figure BDA0002646462750000103
ΔId＝Idcref-Idc，Ucom＝ΔIdRd，Rdto an equivalent virtual resistance, Δ IdIs the current deviation. In the formula of UdiIs a DC side voltage, L0Is equivalent inductance of bridge arm, R0Is equivalent resistance of bridge arm, idiffkFor bridge arm current, UjkFor k-phase bridge arm voltage, UcomIs a common mode voltage component.
Common mode voltage component UcomThe calculation formula of (A) is as follows:
Figure BDA0002646462750000104
in the formula, RdTo an equivalent virtual resistance, Δ IdIs a current deviation, IdcrefFor a given value of the direct-current side current, IdcIs the actual value of the direct current, P*Given the active power for the system to operate,
Figure BDA0002646462750000105
the voltage on the direct current side is given.
The method for acquiring the original MMC bridge arm modulation signal comprises the following steps:
converting abc three-phase alternating current quantity of the MMC current converter into dq coordinates through dq decoupling coordinate transformation;
setting the given values of d-axis and q-axis currents
Figure BDA0002646462750000111
Respectively with the actual value Id、IqThe difference signal of (2) is passed through a PI controller;
combining coupling components of dq axes
Figure BDA0002646462750000112
And dq axis component u of three-phase voltage at alternating current side of MMC convertercd、ucqThe modulation signals are jointly determined.
And (3) building a simulation model on PSCAD simulation software and an RTDS semi-physical simulation platform by combining the direct-current side resonance suppression control block diagram shown in FIG. 6. The specific parameters are as follows: the system capacity is 10MVA, the positive voltage of the direct current side is 10kV, the negative voltage of the direct current side is-10 kV, the system transmits active power of 10MW, the two ends of the system are connected to an active power grid, the MMC1 of the rectification side is used for determining active power control, and the MMC2 of the inversion side is used for determining direct current voltage control.
The PSCAD simulation result graph during steady-state operation of the system is shown in fig. 7, where fig. 7(a) shows no dc-side resonance suppression, fig. 7(b) shows no dc-side resonance suppression, fig. 7(c) shows no dc-side resonance suppression local current graph, fig. 7(d) shows a dc-side resonance suppression local current graph, and fig. 7(e) shows a dc suppression strategy current actual value tracking given value effect graph; the RTDS semi-physical simulation result diagram is shown in fig. 8, where fig. 8(a) shows no dc-side resonance suppression and fig. 8(b) shows dc-side resonance suppression.
According to PSCAD and RTDS simulation results, when the system operates in a steady state, the strategy provided by the invention can effectively inhibit current fluctuation caused by direct current side resonance of the double-end system based on the MMC current converter, and compared with the traditional resonance inhibition strategy, the strategy has the advantages that:
the method has the advantages that a low-pass filter does not need to be additionally designed, the transfer function of the current converter is calculated, and the acquisition information needed by control is reduced.
Secondly, the number of the input sub-modules is adjusted in real time, so that the effect of the damping resistor k is indirectly realized, and the loss of the damping resistor k for system injection is avoided.
The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (10)

1. A double-end system direct current side resonance control method based on an MMC current converter is characterized by comprising the following steps:
obtaining a direct current side current reference value according to the given active power and the direct current side voltage given value when the system operates;
obtaining a current deviation value according to the actual value of the direct current side current and the direct current side current reference value;
obtaining a common-mode voltage component by the current deviation value through a PI controller;
subtracting the common-mode voltage component from the original MMC bridge arm modulation signal to obtain a modified MMC bridge arm modulation signal;
and determining the number of MMC sub-modules actually input in the MMC converter by combining a recent level approximation modulation strategy based on the corrected MMC bridge arm modulation signal, and finishing the direct-current side resonance control of the double-end system based on the MMC converter.
2. The MMC converter-based double-ended system direct-current side resonance control method of claim 1, wherein the common mode voltage component U iscomThe calculation formula of (A) is as follows:
Figure FDA0002646462740000011
in the formula, RdTo an equivalent virtual resistance, Δ IdIs a current deviation, IdcrefFor a given value of the direct-current side current, IdcIs a direct current side currentValue, P*For a given active power at which the system is operating,
Figure FDA0002646462740000012
the voltage on the direct current side is given.
3. The MMC converter-based double-end system direct-current side resonance control method of claim 2, wherein: after completing double-end system direct current side resonance control based on the MMC transverter, the MMC transverter k phase voltage mathematical model is:
Figure FDA0002646462740000013
in the formula of UdiIs a DC side voltage, L0Is equivalent inductance of bridge arm, R0Is equivalent resistance of bridge arm, idiffkFor bridge arm current, UkIs total voltage of k-phase bridge arm, UcomIs a common mode voltage component.
4. The MMC converter-based double-end system direct-current side resonance control method of claim 1, wherein the original MMC bridge arm modulation signal obtaining method comprises the following steps: and obtaining a bridge arm voltage signal by using a PI controller under a synchronous rotating coordinate system, and obtaining an original modulation signal of the MMC bridge arm based on the bridge arm voltage signal and a recent level approximation modulation strategy.
5. The MMC converter-based double-end system direct-current side resonance control method of claim 4, wherein: the method for acquiring the original MMC bridge arm modulation signal comprises the following steps:
converting abc three-phase alternating current quantity of the MMC current converter into dq coordinates through dq decoupling coordinate transformation;
setting the given values of d-axis and q-axis currents
Figure FDA0002646462740000021
Respectively mixing with fruitMargin value Id、IqThe difference signal of (2) is passed through a PI controller;
combining coupling components of dq axes
Figure FDA0002646462740000022
And dq axis component u of three-phase voltage at alternating current side of MMC convertercd、ucqThe modulation signals are jointly determined.
6. The utility model provides a bi-polar system direct current side resonance control system based on MMC transverter which characterized in that includes:
the direct current side current reference value calculating unit is used for solving a direct current side current reference value according to the given active power and the given direct current side voltage value when the system operates;
the current deviation value calculation unit is used for solving a current deviation value according to a direct current side current actual value and the direct current side current reference value;
the common-mode voltage component acquisition unit is used for obtaining a common-mode voltage component by passing the current deviation value through a PI controller; the corrected MMC bridge arm modulation signal calculation unit is used for subtracting the common-mode voltage component from the original MMC bridge arm modulation signal to obtain a corrected MMC bridge arm modulation signal;
and the MMC submodule input quantity determining unit is used for determining the quantity of the MMC submodules actually input into the MMC converter by combining a recent level approximation modulation strategy based on the corrected MMC bridge arm modulation signals, and finishing double-end system direct-current side resonance control based on the MMC converter.
7. The MMC converter-based double-ended system direct current side resonance control system of claim 6, wherein: the common mode voltage component UcomThe calculation formula of (A) is as follows:
Figure FDA0002646462740000023
in the formula, RdIn order to be an equivalent virtual resistance,ΔIdis a current deviation, IdcrefFor a given value of the direct-current side current, IdcIs the actual value of the direct current, P*For a given active power at which the system is operating,
Figure FDA0002646462740000025
the voltage on the direct current side is given.
8. The MMC converter-based double-ended system direct current side resonance control system of claim 7, wherein: after completing double-end system direct current side resonance control based on the MMC transverter, the MMC transverter k phase voltage mathematical model is:
Figure FDA0002646462740000024
in the formula of UdiIs a DC side voltage, L0Is equivalent inductance of bridge arm, R0Is equivalent resistance of bridge arm, idiffkFor bridge arm current, UkIs total voltage of k-phase bridge arm, UcomIs a common mode voltage component.
9. The MMC converter-based double-ended system direct current side resonance control system of claim 6, wherein: the method for acquiring the original MMC bridge arm modulation signal comprises the following steps: and obtaining a bridge arm voltage signal by using a PI controller under a synchronous rotating coordinate system, and obtaining an original modulation signal of the MMC bridge arm based on the bridge arm voltage signal and a recent level approximation modulation strategy.
10. The MMC converter-based double-ended system direct current side resonance control system of claim 9, wherein: the method for acquiring the original MMC bridge arm modulation signal comprises the following steps:
converting abc three-phase alternating current quantity of the MMC current converter into dq coordinates through dq decoupling coordinate transformation;
setting the given values of d-axis and q-axis currents
Figure FDA0002646462740000031
Respectively with the actual value Id、IqThe difference signal of (2) is passed through a PI controller;
combining coupling components of dq axes
Figure FDA0002646462740000032
And dq axis component u of three-phase voltage at alternating current side of MMC convertercd、ucqThe modulation signals are jointly determined.
CN202010856159.9A 2020-08-24 2020-08-24 Double-end system direct current side resonance control method and system based on MMC current converter Pending CN112134472A (en)

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