CN112039113A - Impedance modeling method of NPC type three-phase three-level inverter - Google Patents

Impedance modeling method of NPC type three-phase three-level inverter Download PDF

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CN112039113A
CN112039113A CN202010711643.2A CN202010711643A CN112039113A CN 112039113 A CN112039113 A CN 112039113A CN 202010711643 A CN202010711643 A CN 202010711643A CN 112039113 A CN112039113 A CN 112039113A
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voltage
inverter
current
phase
npc type
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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
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy

Abstract

The invention discloses an impedance modeling method of an NPC type three-phase three-level inverter, wherein the three-level grid-connected inverter adopts direct-current voltage outer loop control and current decoupling inner loop control, frequency coupling caused by neutral point balance control and a phase-locked loop is considered, and an admittance model of the NPC type three-phase three-level inverter is established under a static coordinate system by adopting a harmonic linearization method. The invention has the beneficial effects that: the neutral point balance control is considered, the impedance model of the NPC type three-level inverter is established, the established model can accurately analyze the stability of the NPC type three-level inverter in different power levels and power grid impedance and controller parameters, and theoretical reference can be provided for system parameter design and stability analysis of the NPC type three-level inverter.

Description

Impedance modeling method of NPC type three-phase three-level inverter
Technical Field
The invention relates to the field of renewable energy power generation, in particular to an impedance modeling method of an NPC type three-phase three-level inverter.
Background
In recent years, with the rapid development of renewable energy, a new energy distributed power generation mode represented by wind power and photovoltaic is widely applied. In high-power new energy power generation occasions, a two-level inverter is more and more replaced by a three-level inverter, such as an offshore wind farm. Due to the complex dynamic performance of the grid-connected inverter, the interaction between the inverter and the weak grid may cause stability problems, thereby jeopardizing the safe operation of the grid. In order to analyze the stability problem between the grid-connected inverter and the power grid, a small signal model of the inverter needs to be established. Most of the existing researches are to research a two-level grid-connected inverter. With the rapid development of renewable energy sources, the NPC type three-phase three-level inverter is more and more applied, however, a small-size impedance model of the NPC type three-phase three-level inverter is not established at present.
Therefore, it is necessary to establish an impedance model of the NPC three-level inverter for analyzing the stability of the NPC three-level inverter grid-connected system.
Disclosure of Invention
Aiming at the problems, the invention provides an impedance modeling method of an NPC type three-phase three-level inverter, which solves the difficult problem of impedance modeling of the three-level inverter when neutral point balance control is considered.
In order to solve the technical problems, the technical scheme of the invention is as follows:
an impedance modeling method of an NPC type three-phase three-level inverter is applied to analyzing the stability of an NPC type three-level grid-connected inverter system, and comprises the following steps:
step one, under the ideal power grid, the injection frequency of the PCC of the grid-connected inverter is fpObtaining a three-phase power grid voltage expression by the disturbance voltage;
step two, the three-phase power grid voltage expression is subjected to coordinate transformation to obtain the power grid voltage v under the dq coordinate systemdAnd vqSaid grid voltage vdAnd vqThe voltage V is obtained by using complex variable representation under dq coordinate systemdq；
Thirdly, under a static coordinate system, according to the voltage VdqEstablishing a small signal model of a power level circuit;
step four, under the dq coordinate system, according to the voltage VdqEstablishing a small signal phasor model of a control loop;
establishing a small signal model of the current relation between the AC side and the DC side of the inverter under the dq coordinate system;
step six, obtaining a small signal model of the voltage current relation of the alternating current side of the inverter under the dq coordinate system;
step seven, obtaining the frequency omega according to the models established in the step three to the step sixpAc voltage disturbance of
Figure BDA0002596757810000026
And with DC current disturbances
Figure BDA0002596757810000024
Corresponding admittance Ya0(ωp) (ii) a When the DC voltage is stable, the AC voltage disturbance is calculated
Figure BDA0002596757810000025
With disturbance of alternating current
Figure BDA0002596757810000023
Corresponding admittance Ya1(ωp) And a coupling current
Figure BDA0002596757810000021
Corresponding admittance Ya2(ωp) (ii) a When the direct-current voltage disturbance is considered, the frequency omega is obtained through calculationpDC voltage disturbance of
Figure BDA0002596757810000022
With a corresponding frequency of (ω)p+ω1) And (ω)p-ω1) Between ac current disturbances of01(ωp) And Y02(ωp) (ii) a Calculating to obtain the self-admittance Y between the DC voltage and current disturbances of the inverter00(ωp)；
Step eight, the direct current side capacitors of the three-level inverter are equivalent to be connected in series, and the admittance Y of the direct current side capacitors is obtained through calculationdc(ωp)；
Step nine, calculating the self-admittance Y of the NPC type three-phase three-level inverter according to the disturbance transfer process of the inverter called the direct current sidesa(ωp) And companionRandom admittance Yaa(ωp)。
The invention has the beneficial effects that: the neutral point balance control is considered, the impedance model of the NPC type three-level inverter is established, the established model can accurately analyze the stability of the NPC type three-level inverter in different power levels and power grid impedance and controller parameters, and theoretical reference can be provided for system parameter design and stability analysis of the NPC type three-level inverter.
Drawings
Fig. 1 is a main circuit topology and control structure diagram of an NPC type three-level inverter in an embodiment of the present invention;
fig. 2 is a control block diagram of an NPC type three-level inverter in an embodiment of the present invention;
FIG. 3 is a block diagram of small signal disturbance of an NPC type three-level inverter in an embodiment of the present invention;
fig. 4 shows an impedance model and simulation measurement results of an NPC type three-level inverter 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.
As shown in fig. 1, the main circuit consists of 12 IGBTs and 6 anti-parallel diodes, and adopts SVPWM modulation; the alternating current filter adopts an L-shaped filter; z is equivalent grid impedance; v. ofabcIs the equivalent grid voltage; i.e. iabcIs the current at the PCC point; v. ofdc、idcThe voltage and the current of the DC side of the inverter.
As shown in fig. 2, the control circuit adopts a direct current voltage to control the outer loop and a current decoupling inner loop.
On the basis of the main circuit topology and the control structure of the NPC type three-level inverter and the control method, the embodiment provides an impedance modeling method of the NPC type three-phase three-level inverter, which is applied to analyzing the stability of an NPC type three-level grid-connected inverter system, and comprises the following steps:
step one, under the ideal power grid, the injection frequency of the PCC of the grid-connected inverter is fpObtaining a three-phase power grid voltage expression by the disturbance voltage;
Figure BDA0002596757810000031
step two, the three-phase power grid voltage expression is subjected to coordinate transformation to obtain the power grid voltage v under the dq coordinate systemdAnd vqSaid grid voltage vdAnd vqThe voltage V is obtained by using complex variable representation under dq coordinate systemdq；
Thirdly, under a static coordinate system, according to the voltage VdqEstablishing a small signal model of a power level circuit;
step four, under the dq coordinate system, according to the voltage VdqEstablishing a small signal phasor model of a control loop;
establishing a small signal model of the current relation between the AC side and the DC side of the inverter under the dq coordinate system;
step six, obtaining a small signal model of the voltage current relation of the alternating current side of the inverter under the dq coordinate system;
step seven, obtaining the frequency omega according to the models established in the step three to the step sixpAc voltage disturbance of
Figure BDA0002596757810000032
And with DC current disturbances
Figure BDA0002596757810000033
Corresponding admittance Ya0(ωp) (ii) a When the DC voltage is stable, the AC voltage disturbance is calculated
Figure BDA0002596757810000034
With exchange ofCurrent perturbation
Figure BDA0002596757810000035
Corresponding admittance Ya1(ωp) And coupling the current
Figure BDA0002596757810000036
Corresponding admittance Ya2(ωp) (ii) a When the direct-current voltage disturbance is considered, the frequency omega is obtained through calculationpDC voltage disturbance of
Figure BDA0002596757810000037
With a corresponding frequency of (ω)p+ω1) And (ω)p-ω1) Between ac current disturbances of01(ωp) And Y02(ωp) (ii) a Calculating to obtain the self-admittance Y between the DC voltage and current disturbances of the inverter00(ωp)；
Step eight, when the neutral point disturbance current acts on the neutral point on the direct current side, the disturbance voltage amplitudes of the upper capacitor and the lower capacitor are the same. When the capacitors are unbalanced, only the current disturbance on the capacitors is influenced, the sum of the voltage disturbance of the two capacitors is always zero, and the disturbance of the neutral point on the direct current side does not influence the voltage of the capacitors on the direct current side, so that the capacitors on the direct current side of the three-level inverter can be equivalently connected in series, and the admittance Y of the capacitors on the direct current side is obtained through calculationdc(ωp)；
Step nine, deriving and obtaining the self-admittance Y of the NPC type three-phase three-level inverter according to the disturbance transfer process of the inverter called the direct current sidesa(ωp) And concomitant admittance Yaa(ωp)。
The neutral point balance control is considered, the impedance model of the NPC type three-phase three-level inverter is established, the established model can accurately analyze the stability of the NPC type three-level inverter in different power levels, power grid impedance and controller parameters, and theoretical reference can be provided for system parameter design and stability analysis of the NPC type three-level inverter.
Furthermore, in step three, the small signal model of the power stage circuit is specifically:
Figure BDA0002596757810000041
wherein, ω ispIs the disturbance frequency; omega1Is the fundamental frequency of the power grid; l is a filter inductance value;
Figure BDA0002596757810000042
is the frequency (omega) under the dq coordinate systemp-ω1) Current perturbation of (2);
Figure BDA0002596757810000043
is a frequency of (ω)p-ω1) The DC voltage disturbance of (2); vdcIs a direct current voltage value;
Figure BDA0002596757810000044
is a frequency of (ω)p-ω1) The inverter duty cycle of (a); ddqIs the steady state value of the inverter duty cycle under the dq coordinate system; denotes the conjugate of the complex number.
Furthermore, in step four, the small-signal phasor model of the control loop specifically includes:
Figure BDA0002596757810000045
wherein the content of the first and second substances,
Figure BDA0002596757810000046
is a frequency of (ω)p-ω1) The inverter duty cycle of (a); vcrIs equivalent carrier amplitude, 2Vcr＝Vdc；Gc(ωp-ω1) Is the transfer function of a current loop PI regulator, Gv(ωp-ω1) Is the transfer function of the voltage loop PI regulator.
Further, in step five, the small-signal model of the current relationship between the ac side and the dc side of the inverter is specifically:
Figure BDA0002596757810000047
wherein denotes the conjugate of the complex number; i isdqIs an alternating current in dq coordinate system.
Further, in step six, the voltage-current relationship at the ac side of the inverter is specifically as follows:
Figure BDA0002596757810000048
wherein, VcrIs equivalent carrier amplitude, 2Vcr＝Vdc，
Figure BDA0002596757810000049
Is a frequency of (ω)p-ω1) Duty cycle of inverter of Gc(ωp-ω1) Is the transfer function of a current loop PI regulator, Gv(ωp-ω1) Is the transfer function of the voltage loop PI regulator.
As shown in fig. 3, in the figure,
Figure BDA00025967578100000410
is that the frequency of the AC side is omegapVoltage, current disturbances;
Figure BDA00025967578100000411
is generated by PLL and DC voltage loop with frequency of (omega)p-2ω1) The coupling current of (a);
Figure BDA00025967578100000412
is the voltage and current disturbance on the direct current side; omegaPIs the disturbance frequency; omegaωIs the fundamental frequency of the grid. The self-admittance Y can be obtained according to the perturbation diagramsa(ωp) And concomitant admittance Yaa(ωp). In the ninth step, the self-admittance Ysa(ωp) The method specifically comprises the following steps:
Figure BDA0002596757810000051
the adjoint admittance Yaa(ωp) The method specifically comprises the following steps:
Figure BDA0002596757810000052
where denotes the conjugate of the complex number.
As shown in fig. 4, wherein the solid line is a bode diagram obtained based on an impedance mathematical model; the dotted line is the simulation measured impedance result of the NPC type three-level inverter; as can be seen from the figure: the result of the impedance measurement can be well matched with the result of the established mathematical model, and the correctness of the established model is proved.
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 (6)

1. An impedance modeling method of an NPC type three-phase three-level inverter is characterized by being applied to analyzing the stability of an NPC type three-level grid-connected inverter system and comprising the following steps of:
step one, under the ideal power grid, the injection frequency of the PCC of the grid-connected inverter is fpObtaining a three-phase power grid voltage expression by the disturbance voltage;
step two, the three-phase power grid voltage expression is subjected to coordinate transformation to obtain the power grid voltage v under the dq coordinate systemdAnd vqSaid grid voltage vdAnd vqThe voltage V is obtained by using complex variable representation under dq coordinate systemdq；
Thirdly, under a static coordinate system, according to the voltage VdqEstablishing a small signal model of a power level circuit;
step four, under the dq coordinate system, according to the voltage VdqEstablishing a small signal phasor model of a control loop;
establishing a small signal model of the current relation between the AC side and the DC side of the inverter under the dq coordinate system;
step six, obtaining a small signal model of the voltage current relation of the alternating current side of the inverter under the dq coordinate system;
step seven, obtaining the frequency omega according to the models established in the step three to the step sixpAc voltage disturbance of
Figure FDA0002596757800000011
And with DC current disturbances
Figure FDA0002596757800000012
Corresponding admittance Ya0(ωp) (ii) a When the DC voltage is stable, the AC voltage disturbance is calculated
Figure FDA0002596757800000013
With disturbance of alternating current
Figure FDA0002596757800000014
Corresponding admittance Ya1(ωp) And a coupling current
Figure FDA0002596757800000015
Corresponding admittance Ya2(ωp) (ii) a When the direct-current voltage disturbance is considered, the frequency omega is obtained through calculationpDC voltage disturbance of
Figure FDA0002596757800000016
With a corresponding frequency of (ω)p+ω1) And (ω)p-ω1) Between ac current disturbances of01(ωp) And Y02(ωp) (ii) a Calculating to obtain the self-admittance Y between the DC voltage and current disturbances of the inverter00(ωp)；
Step eight, the direct current side capacitors of the three-level inverter are equivalent to be connected in series, and the admittance Y of the direct current side capacitors is obtained through calculationdc(ωp)；
Step nine, calculating the self-admittance Y of the NPC type three-phase three-level inverter according to the disturbance transfer process of the inverter called the direct current sidesa(ωp) And concomitant admittance Yaa(ωp)。
2. The impedance modeling method of an NPC type three-phase three-level inverter of claim 1,
the small signal model of the power level circuit is specifically as follows:
Figure FDA0002596757800000017
wherein, ω ispIs the disturbance frequency; omega1Is the fundamental frequency of the power grid; l is a filter inductance value;
Figure FDA0002596757800000018
is the frequency (omega) under the dq coordinate systemp-ω1) Current perturbation of (2);
Figure FDA0002596757800000019
is a frequency of (ω)p-ω1) The DC voltage disturbance of (2); vdcIs a direct current voltage value;
Figure FDA0002596757800000021
is a frequency of (ω)p-ω1) The inverter duty cycle of (a); ddqIs the steady state value of the inverter duty cycle under the dq coordinate system; denotes the conjugate of the complex number.
3. The impedance modeling method of an NPC type three-phase three-level inverter of claim 2,
the small-signal phasor model of the control loop specifically comprises the following steps:
Figure FDA0002596757800000022
wherein the content of the first and second substances,
Figure FDA0002596757800000023
is a frequency of (ω)p-ω1) The inverter duty cycle of (a); vcrIs equivalent carrier amplitude, 2Vcr＝Vdc；Gc(ωp-ω1) Is the transfer function of a current loop PI regulator, Gv(ωp-ω1) Is the transfer function of the voltage loop PI regulator.
4. The impedance modeling method of an NPC type three-phase three-level inverter of claim 3,
the small-signal model of the current relationship between the alternating current side and the direct current side of the inverter is specifically as follows:
Figure FDA0002596757800000024
wherein denotes the conjugate of the complex number; i isdqIs an alternating current in dq coordinate system.
5. The impedance modeling method of an NPC type three-phase three-level inverter of claim 4,
the small-signal model of the voltage-current relation of the alternating-current side of the inverter is specifically as follows:
Figure FDA0002596757800000025
6. the impedance modeling method of an NPC type three-phase three-level inverter of claim 5,
the self admittance Ysa(ωp) The method specifically comprises the following steps:
Figure FDA0002596757800000026
the adjoint admittance Yaa(jωp) The method specifically comprises the following steps:
Figure FDA0002596757800000027
where denotes the conjugate of the complex number.
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116418049A (en) * 2023-06-08 2023-07-11 四川大学 Accurate admittance modeling method for sagging-controlled three-phase grid-connected inverter

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
BO ZHANG等: "Impedance modeling and stability analysis of a three-phase three-level NPC inverter connected to the grid", 《CSEE JOURNAL OF POWER AND ENERGY SYSTEMS》 *
王国宁等: "用于三相并网逆变器稳定性分析的自导纳和伴随导纳建模", 《中国电机工程学报》 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116418049A (en) * 2023-06-08 2023-07-11 四川大学 Accurate admittance modeling method for sagging-controlled three-phase grid-connected inverter
CN116418049B (en) * 2023-06-08 2023-08-11 四川大学 Accurate admittance modeling method for sagging-controlled three-phase grid-connected inverter

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Application publication date: 20201204