CN117096897A - Method for participating in grid frequency modulation support of two-stage type photovoltaic grid-connected power generation system - Google Patents

Method for participating in grid frequency modulation support of two-stage type photovoltaic grid-connected power generation system Download PDF

Info

Publication number
CN117096897A
CN117096897A CN202310891656.6A CN202310891656A CN117096897A CN 117096897 A CN117096897 A CN 117096897A CN 202310891656 A CN202310891656 A CN 202310891656A CN 117096897 A CN117096897 A CN 117096897A
Authority
CN
China
Prior art keywords
power
grid
voltage
vsg
photovoltaic
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
CN202310891656.6A
Other languages
Chinese (zh)
Inventor
柏晶晶
袁源
包继
王泓法
郑杨
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Yancheng Power Supply Co of State Grid Jiangsu Electric Power Co Ltd
Original Assignee
Yancheng Power Supply Co of State Grid Jiangsu Electric Power Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Yancheng Power Supply Co of State Grid Jiangsu Electric Power Co Ltd filed Critical Yancheng Power Supply Co of State Grid Jiangsu Electric Power Co Ltd
Priority to CN202310891656.6A priority Critical patent/CN117096897A/en
Publication of CN117096897A publication Critical patent/CN117096897A/en
Pending legal-status Critical Current

Links

Classifications

    • 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
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • 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
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • 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
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/466—Scheduling the operation of the generators, e.g. connecting or disconnecting generators to meet a given demand
    • 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
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/48—Controlling the sharing of the in-phase component
    • 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
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/50—Controlling the sharing of the out-of-phase component
    • 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
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
    • 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
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

The invention discloses a method for participating in grid frequency modulation support of a two-stage photovoltaic grid-connected power generation system, which comprises the following steps: detecting the voltage of a photovoltaic direct current bus, and obtaining the maximum output state through an MPPT unit; active power which can participate in frequency modulation is reserved through load shedding control; tracking the power electricity after load shedding through power tracking; detecting the regulated voltage, controlling and regulating the duty ratio of a Boost circuit, and maintaining the DC voltage of the Boost bus to be stable; and detecting whether the grid frequency deviates or not, and regulating the grid frequency through the VSG. The method provided by the invention combines load shedding control and the virtual synchronous machine, so that the photovoltaic system can spontaneously participate in frequency modulation, and the VSG can participate in the frequency modulation of the power system.

Description

Method for participating in grid frequency modulation support of two-stage type photovoltaic grid-connected power generation system
Technical Field
The invention belongs to the field of active support control of photovoltaic power generation and photovoltaic grid-connected frequency, and particularly relates to a method for a two-stage photovoltaic grid-connected power generation system to participate in grid frequency modulation support.
Background
As the traditional fossil energy reserves are gradually reduced and the environmental problems caused by combustion are increasingly prominent, people are urgent to develop clean and pollution-free new energy power generation technologies, and more new energy power generators are also being put into the power system in China, wherein the photovoltaic power generation not only meets the power consumption requirements of users, but also overcomes the defects of fossil energy because of the characteristics of mature technology and low cost. However, the increase of the power generation duty ratio of the new energy can cause the photovoltaic power generation system to show low damping characteristic in operation, and the grid-connected system is easy to lack frequency modulation capability. When the power balance of the generator side and the load is destroyed and a power shortage phenomenon occurs, the power shortage phenomenon can lead to the fluctuation of the system frequency, and if the frequency cannot be modulated, the system stability can be affected.
In order to enable the photovoltaic generator set to have the capability of participating in primary frequency modulation, students at home and abroad focus on the improvement of a control strategy of the new energy grid-connected converter. Because the photovoltaic unit does not contain a rotating element, the system lacks inertia, and only the load shedding control or active standby in an energy storage mode can be utilized to provide the frequency adjustment capability. The invention selects the strategy of load shedding control.
Disclosure of Invention
The invention aims to solve the technical problem of overcoming the defects of the prior art and provides a method for enabling a two-stage photovoltaic grid-connected power generation system to participate in power grid frequency modulation support.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a method for participating in grid frequency modulation support of a two-stage photovoltaic grid-connected power generation system comprises the following steps:
step S 1 The photovoltaic array is merged after passing through a Boost circuit and an LC three-level inverter in sequencePower grid, direct current bus voltage U after voltage boost detection dc ；
Step S 2 Active power capable of participating in frequency modulation is reserved through the load shedding control unit, the duty ratio of the Boost circuit is changed through the power tracking unit, so that the photovoltaic power generation system works near a power point after load shedding, and the photovoltaic power generation system is ensured to leave enough active power;
step S 3 The reactive ring unit needs to read voltage and current parameters at the PCC of the power grid side and calculate reactive power; the active loop unit reads the boosted direct current bus voltage and sends the direct current bus voltage and the grid-side reactive power into the VSG as reference values, and the virtual impedance and the voltage current double closed loop unit are modulated to change the duty ratio of the inverter, so that the grid-connected system can participate in frequency modulation and keep the system stable.
Further, the step S 1 The method specifically comprises the following steps:
S 1.1 establishing a photovoltaic power generation system front-stage Boost circuit model;
S 1.2 and establishing a rear-stage LC-type grid-connected inverter model of the photovoltaic power generation system.
Further, the step S 1.1 The method comprises the following steps:
S 1.1.1 input-output voltage for Boost circuit, i.e. photovoltaic power supply U pv And DC bus voltage U dc The following relationship exists:
wherein d is the duty cycle;
S 1.1.2 the DC current passes through the LC-type inverter and then outputs three-phase voltage and current u at the inverter side 1abc And i 1abc Network-side three-phase voltage-current data u can be obtained at PCC abc And i 2abc The relation is as follows:
wherein L is the inductance of the filter, L g Is the equivalent inductance of the power grid, C is the filter capacitance, u c-abc For the three-phase voltage of the filter capacitor e abc For three-phase network voltage, U NN’ Is the voltage between the neutral point of the filter capacitor and the neutral point of the power grid.
Further, the step S 2 The method comprises the following steps:
S 2.1 the MPPT unit receives the sampled photovoltaic power supply voltage U pv And current I pv Obtaining the maximum power point P max Then, the output power P is input into a load shedding control unit and output under the load shedding control o ：
P o ＝P max ×(1-δ)
Wherein delta is the load shedding rate of the photovoltaic;
S 2.2 the droop control unit causes the system to vary (f n -f) quantity adjusting the output power, resulting in a change in output power Δp expressed as:
ΔP＝K×(f n -f)
wherein K is a sag factor, (f) n -f) is the system frequency deviation;
S 2.3 the power tracking unit receives a photovoltaic power supply U pv And a voltage reference U ref And outputs a duty cycle d to adjust the Boost circuit so that the system operates near the power point after load shedding.
Further, the step S 3 The method comprises the following steps:
S 3.1 by reading the net side voltage current u abc And i 2abc And converted to the αβ coordinate system:
S 3.2 calculating network side active and reactive power P e And Q e ：
P e ＝U α I 2α +U β I 2β
Q e ＝U β I 2α -U α I 2β
S 3.3 For the active ring unit, the DC bus voltage U is read from the DC bus side dc The reference value P of active power at the output network side is input into a PI controller together with the reference value of the DC bus voltage ref2 Then, PCC is sampled and calculated to obtain network side active power Pe and Pref2, the network side active power Pe and Pref2 are input into a VSG active link, and the active link is output as a VSG virtual internal potential phase angle theta; VSG virtual internal potential phase angle θ with input: virtual electromagnetic power P e And active power of VSG given P ref The relation of (2) is:
wherein J is virtual moment of inertia of VSG, ω is VSG output angular frequency, D p For the sag-damping coefficient, θ is the virtual internal potential phase angle of VSG, ω n Is the rated angular frequency;
S 3.4 the reactive voltage control equation of the reactive ring unit is as follows:
wherein E is r Is virtual internal potential effective value, K q For exciting integral coefficient, U n Is the rated voltage effective value, U is the grid-connected voltage effective value, D q For reactive-voltage sag factor, Q ref For giving reactive power to the system, Q e Outputting reactive power for the system;
S 3.5 obtaining VSG three-phase virtual internal potential e through active loop and reactive loop a 、e b And e c The expression of (2) is:
S 3.6 the virtual impedance control can enable the grid-connected system to obtain the electrical characteristics of the stator of the synchronous generator, and the expression is as follows:
wherein R is v And L v Virtual resistance and virtual inductance; e, e α And e β For the internal potential e of VSG a 、e b 、e c An alpha beta axis component of (2); i.e α And i β An alpha-beta axis component of the system network access current; u (u) αref And u βref The reference component of the alpha beta axis of the voltage loop is output for the virtual impedance link;
S 3.7 will u αref And u βref And inputting a VSG voltage loop to obtain a current loop reference value:
g in 1 (s) is an expression of the PI controller 1
After the reference value of the current loop is obtained, tracking control is carried out on the network access current of the grid-connected system through the current loop, and the expression is as follows:
g in 2 (s) is the expression of the PI controller 2, u is the current loop output iα 、u iβ And an alpha beta axis component serving as an inverter modulation wave is used for generating a driving signal through an SPWM link to control the on and off of a switching tube of the inverter.
Compared with the prior art, the invention has the beneficial effects that: the method provided by the invention combines load shedding control and the virtual synchronous machine, so that the photovoltaic system can spontaneously participate in frequency modulation, and the VSG can participate in the frequency modulation of the power system.
Drawings
Fig. 1 is a schematic circuit diagram of a two-stage photovoltaic grid-connected power generation system participating in grid frequency modulation support.
Fig. 2 is a photovoltaic grid-tie pre-circuit.
Fig. 3 is a main circuit structure of the LC-type three-level grid-connected inverter system.
Fig. 4 is a flow chart of a power tracking module.
Fig. 5 (a) - (d) are waveforms of active power, reactive power, voltage effective value and current effective value output by the grid-connected system when the frequency drops suddenly.
Fig. 6 (a) - (d) are waveforms of active power, reactive power, voltage effective value and current effective value output by the grid-connected system during frequency sudden increase.
Detailed Description
Various exemplary embodiments of the invention will now be described in detail, which should not be considered as limiting the invention, but rather as more detailed descriptions of certain aspects, features and embodiments of the invention.
It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In addition, for numerical ranges in this disclosure, it is understood that each intermediate value between the upper and lower limits of the ranges is also specifically disclosed. Every smaller range between any stated value or stated range, and any other stated value or intermediate value within the stated range, is also encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.
It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the invention described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from consideration of the specification of the present invention. The specification and examples of the present invention are exemplary only.
As used herein, the terms "comprising," "including," "having," "containing," and the like are intended to be inclusive and mean an inclusion, but not limited to.
Aiming at a two-stage photovoltaic grid-connected system, load shedding control is commonly used for solving the power unbalance of the generator side and the load power, but the system still lacks stability, so that VSG control is added to a grid-connected part for secondary frequency modulation and the stability of the system is increased. As shown in fig. 1.
The conventional VSG control strategy cannot be adjusted in time according to the condition of the photovoltaic power generation part of the front stage, so that the direct-current bus voltage Udc is selected as the input quantity of the active ring.
The invention provides a method for enabling a photovoltaic power generation system to have active power capable of participating in frequency modulation by using load shedding control and combining VSG control, comprising the following steps:
1. sampling to obtain direct current I output by photovoltaic power supply pv Sum voltage U pv 。
2. And obtaining the maximum power point MPP through an MPPT module.
3. Active power reference value P obtained by load shedding control and droop control ref 。
4. The photovoltaic power generation system works near the power point after load shedding through the power tracking module
5. Sampling to obtain three-phase voltage u at network side a 、u b 、u c And three-phase current i 2a 、i 2b 、i 2c U is obtained by Clark conversion of the voltage and the current at the network side α 、u β 、i α 、i β 。
6. Calculating to obtain reactive power Q by using voltage and current components under the alpha beta coordinate system obtained in the step 5, and obtaining amplitude of VSG virtual internal potential through a reactive ring
7. And reading the voltage of the direct current bus and obtaining the phase angle theta of the virtual internal potential of the VSG through the active loop.
8. Obtained in steps 6 and 7And θ, and net side three-phase current i obtained by sampling 2abc Obtaining a voltage ring alpha beta axis reference component u through a virtual impedance control module αref And u βref 。
9. U obtained in step 8 αref And u βref The alpha beta axis component u of the inverter modulation wave is obtained through voltage and current double closed-loop control iα And u iβ And generating a driving signal through an SPWM link to control the on and off of the switching tube of the inverter.
Specifically, a method for participating in grid frequency modulation support by a two-stage photovoltaic grid-connected power generation system comprises the following steps:
step S 1 The photovoltaic array is sequentially combined into a power grid after passing through a Boost circuit and an LC three-level inverter, and the boosted DC bus voltage U is detected dc 。
Step S 2 Active power capable of participating in frequency modulation is reserved through the load shedding control unit, the duty ratio of the Boost circuit is changed through the power tracking unit, so that the photovoltaic power generation system works near a power point after load shedding, and the photovoltaic power generation system is ensured to leave enough active power.
Step S 3 The reactive ring unit needs to read the voltage and current parameters at the grid side PCC to calculate reactive power. The active loop unit reads the boosted DC bus voltage and sends the boosted DC bus voltage and the grid-side reactive power into the VSG as reference values, and the virtual impedance and the voltage double closed loop unit are modulated to change the duty cycle of the inverterCompared with the prior art, the grid-connected system can participate in frequency modulation and keep the system stable.
Said step S 1 The method comprises the following steps:
S 1.1 and establishing a photovoltaic power generation system front-stage Boost circuit model.
S 1.2 And establishing a rear-stage LC-type grid-connected inverter model of the photovoltaic power generation system.
Said step S 1.1 The method comprises the following steps:
S 1.1.1 the Boost circuit is shown in FIG. 2, and the input and output voltages of the Boost circuit, namely the photovoltaic power supply U pv And DC bus voltage U dc The following relationship exists:
where d is the duty cycle.
S 1.1.2 The grid-connected system of the inverter is shown in fig. 3, and the direct current passes through the LC-type inverter to output three-phase voltage and current u at the inverter side 1abc And i 1abc Network-side three-phase voltage-current data u can be obtained at PCC abc And i 2abc The relation is as follows:
wherein L is the inductance of the filter, L g Is the equivalent inductance of the power grid, C is the filter capacitance, u c-abc For the three-phase voltage of the filter capacitor e abc For three-phase network voltage, U NN’ Is the voltage between the neutral point of the filter capacitor and the neutral point of the power grid.
Said step S 2 The method comprises the following steps:
S 2.1 the MPPT unit receives the sampled photovoltaic power supply voltage U pv And current I pv Obtaining the maximum power point P max Then, the output power P is input into a load shedding control unit and output under the load shedding control o ：
P o ＝P max ×(1-δ)
Where δ is the photovoltaic load shedding rate.
S 2.2 The droop control unit causes the system to vary (f n -f) quantity adjusting the output power, resulting in a change in output power Δp expressed as:
ΔP＝K×(f n -f)
wherein K is a sag factor, (f) n -f) is the system frequency deviation.
S 2.3 The power tracking unit receives a photovoltaic power supply U pv And a voltage reference U ref And outputs a duty cycle d to adjust the Boost circuit so that the system operates near the power point after load shedding. A flow chart of power tracking is shown in fig. 4.
Said step S 3 The method comprises the following steps:
S 3.1 by reading the net side voltage current u abc And i 2abc And converted to the αβ coordinate system:
S 3.2 calculating network side active and reactive power P e And Q e ：
P e ＝U α I 2α +U β I 2β
Q e ＝U β I 2α -U α I 2β
S 3.3 For the active ring unit, the DC bus voltage U is read from the DC bus side dc The reference value P of active power at the output network side is input into a PI controller together with the reference value of the DC bus voltage ref2 Then PCC is sampled and calculated to obtain network side active power Pe and Pref2 which are input into VSG active link and output from active linkIs the virtual internal potential phase angle θ of VSG. VSG virtual internal potential phase angle θ with input: virtual electromagnetic power P e And active power of VSG given P ref The relation of (2) is:
wherein J is virtual moment of inertia of VSG, ω is VSG output angular frequency, D p For the sag-damping coefficient, θ is the virtual internal potential phase angle of VSG, ω n Is the rated angular frequency.
S 3.4 The reactive voltage control equation of the reactive ring unit is as follows:
wherein E is r Is virtual internal potential effective value, K q For exciting integral coefficient, U n Is the rated voltage effective value, U is the grid-connected voltage effective value, D q For reactive-voltage sag factor, Q ref For giving reactive power to the system, Q e Reactive power is output for the system.
S 3.5 Obtaining VSG three-phase virtual internal potential e through active loop and reactive loop a 、e b And e c The expression of (2) is:
S 3.6 the virtual impedance control can enable the grid-connected system to obtain the electrical characteristics of the stator of the synchronous generator, and the expression is as follows:
wherein R is v And L v Virtual resistance and virtual inductance; e, e α And e β For the internal potential e of VSG a 、e b 、e c An alpha beta axis component of (2); i.e α And i β An alpha-beta axis component of the system network access current; u (u) αref And u βref And outputting a voltage loop alpha beta axis reference component for the virtual impedance link.
S 3.7 Will u αref And u βref And inputting a VSG voltage loop to obtain a current loop reference value:
g in 1 (s) is an expression of the PI controller 1
After the reference value of the current loop is obtained, tracking control is carried out on the network access current of the grid-connected system through the current loop, and the expression is as follows:
g in 2 (s) is the expression of the PI controller 2, u is the current loop output iα 、u iβ And an alpha beta axis component serving as an inverter modulation wave is used for generating a driving signal through an SPWM link to control the on and off of a switching tube of the inverter.
According to the embodiment, a load shedding operation simulation model applicable to the photovoltaic grid-connected power generation system is built based on MATLAB/Simulink. The grid-connected targets are as follows: when the power grid is suddenly changed in frequency of +/-0.5 Hz, the system can spontaneously modulate frequency and maintain stability. Specific parameters are shown in the following tables 1 to 3, simulation results are shown in fig. 5 to 6, fig. 5 (a) to (d) are waveforms of active power, reactive power, voltage effective value and current effective value output by the grid-connected system when the frequency suddenly drops, and fig. 6 (a) to (d) are waveforms of active power, reactive power, voltage effective value and current effective value output by the grid-connected system when the frequency suddenly drops.
Table 1 LC Filter and Q-V parameters
Table 3 photovoltaic array parameters
The control target that photovoltaic participates in frequency modulation and keeps the stability of the power grid can be effectively achieved through the method.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the particular embodiments disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Claims (5)

1. A method for participating in grid frequency modulation support of a two-stage photovoltaic grid-connected power generation system is characterized by comprising the following steps of: comprises the following steps:
step S 1 The photovoltaic array is sequentially combined into a power grid after passing through a Boost circuit and an LC three-level inverter, and the boosted DC bus voltage U is detected dc ；
Step S 2 Active power capable of participating in frequency modulation is reserved through the load shedding control unit, the duty ratio of the Boost circuit is changed through the power tracking unit, so that the photovoltaic power generation system works near a power point after load shedding, and the photovoltaic power generation system is ensured to leave enough active power;
step S 3 The reactive ring unit needs to read voltage and current parameters at the PCC of the power grid side and calculate reactive power; the active loop unit reads the boosted direct current bus voltage and sends the direct current bus voltage and the grid-side reactive power into the VSG as reference values, and the virtual impedance and the voltage current double closed loop unit are modulated to change the duty ratio of the inverter, so that the grid-connected system can participate in frequency modulation and keep the system stable.
2. A two-stage photovoltaic grid-connected generator according to claim 1The method for the electric system to participate in the frequency modulation support of the power grid is characterized in that the step S 1 The method specifically comprises the following steps:
S 1.1 establishing a photovoltaic power generation system front-stage Boost circuit model;
S 1.2 and establishing a rear-stage LC-type grid-connected inverter model of the photovoltaic power generation system.
3. The method for participating in grid frequency modulation support of a two-stage grid-connected photovoltaic power generation system according to claim 2, wherein the step S 1.1 The method comprises the following steps:
S 1.1.1 input-output voltage for Boost circuit, i.e. photovoltaic power supply U pv And DC bus voltage U dc The following relationship exists:
wherein d is the duty cycle;
S 1.1.2 the DC current passes through the LC-type inverter and then outputs three-phase voltage and current u at the inverter side 1abc And i 1abc Network-side three-phase voltage-current data u can be obtained at PCC abc And i 2abc The relation is as follows:
wherein L is the inductance of the filter, L g Is the equivalent inductance of the power grid, C is the filter capacitance, u c-abc For the three-phase voltage of the filter capacitor e abc For three-phase network voltage, U NN’ Is the voltage between the neutral point of the filter capacitor and the neutral point of the power grid.
4. The method for participating in grid frequency modulation support of a two-stage grid-connected photovoltaic power generation system according to claim 1, wherein the step S 2 The method comprises the following steps:
S 2.1 the MPPT unit receives the sampled photovoltaic power supply voltage U pv And current I pv Obtaining the maximum power point P max Then, the output power P is input into a load shedding control unit and output under the load shedding control o ：
P o ＝P max ×(1-δ)
Wherein delta is the load shedding rate of the photovoltaic;
S 2.2 the droop control unit causes the system to vary (f n -f) quantity adjusting the output power, resulting in a change in output power Δp expressed as:
ΔP＝K×(f n -f)
wherein K is a sag factor, (f) n -f) is the system frequency deviation;
S 2.3 the power tracking unit receives a photovoltaic power supply U pv And a voltage reference U ref And outputs a duty cycle d to adjust the Boost circuit so that the system operates near the power point after load shedding.
5. The method for participating in grid frequency modulation support of a two-stage grid-connected photovoltaic power generation system according to claim 1, wherein the step S 3 The method comprises the following steps:
S 3.1 by reading the net side voltage current u abc And i 2abc And converted to the αβ coordinate system:
S 3.2 calculating network side active and reactive power P e And Q e ：
P e ＝U α I 2α +U β I 2β
Q e ＝U β I 2α -U α I 2β
S 3.3 For the active ring unit, the DC bus voltage U is read from the DC bus side dc The reference value P of active power at the output network side is input into a PI controller together with the reference value of the DC bus voltage ref2 Then, PCC is sampled and calculated to obtain network side active power Pe and Pref2, the network side active power Pe and Pref2 are input into a VSG active link, and the active link is output as a VSG virtual internal potential phase angle theta; VSG virtual internal potential phase angle θ with input: virtual electromagnetic power P e And active power of VSG given P ref The relation of (2) is:
wherein J is virtual moment of inertia of VSG, ω is VSG output angular frequency, D p For the sag-damping coefficient, θ is the virtual internal potential phase angle of VSG, ω n Is the rated angular frequency;
S 3.4 the reactive voltage control equation of the reactive ring unit is as follows:
wherein E is r Is virtual internal potential effective value, K q For exciting integral coefficient, U n Is the rated voltage effective value, U is the grid-connected voltage effective value, D q For reactive-voltage sag factor, Q ref For giving reactive power to the system, Q e Outputting reactive power for the system;
S 3.5 obtaining VSG three-phase virtual internal potential e through active loop and reactive loop a 、e b And e c The expression of (2) is:
S 3.6 the virtual impedance control can enable the grid-connected system to obtain the electrical characteristics of the stator of the synchronous generator, and the expression is as follows:
wherein R is v And L v Virtual resistance and virtual inductance; e, e α And e β For the internal potential e of VSG a 、e b 、e c An alpha beta axis component of (2); i.e α And i β An alpha-beta axis component of the system network access current; u (u) αref And u βref The reference component of the alpha beta axis of the voltage loop is output for the virtual impedance link;
S 3.7 will u αref And u βref And inputting a VSG voltage loop to obtain a current loop reference value:
g in 1 (s) is an expression of the PI controller 1
After the reference value of the current loop is obtained, tracking control is carried out on the network access current of the grid-connected system through the current loop, and the expression is as follows:
g in 2 (s) is the expression of the PI controller 2, u is the current loop output iα 、u iβ And an alpha beta axis component serving as an inverter modulation wave is used for generating a driving signal through an SPWM link to control the on and off of a switching tube of the inverter.
CN202310891656.6A 2023-07-20 2023-07-20 Method for participating in grid frequency modulation support of two-stage type photovoltaic grid-connected power generation system Pending CN117096897A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202310891656.6A CN117096897A (en) 2023-07-20 2023-07-20 Method for participating in grid frequency modulation support of two-stage type photovoltaic grid-connected power generation system

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202310891656.6A CN117096897A (en) 2023-07-20 2023-07-20 Method for participating in grid frequency modulation support of two-stage type photovoltaic grid-connected power generation system

Publications (1)

Publication Number Publication Date
CN117096897A true CN117096897A (en) 2023-11-21

Family

ID=88776370

Family Applications (1)

Application Number Title Priority Date Filing Date
CN202310891656.6A Pending CN117096897A (en) 2023-07-20 2023-07-20 Method for participating in grid frequency modulation support of two-stage type photovoltaic grid-connected power generation system

Country Status (1)

Country Link
CN (1) CN117096897A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117856642A (en) * 2024-03-06 2024-04-09 东南大学 Network construction control method and medium applied to multiport optical storage integrated converter

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117856642A (en) * 2024-03-06 2024-04-09 东南大学 Network construction control method and medium applied to multiport optical storage integrated converter
CN117856642B (en) * 2024-03-06 2024-05-10 东南大学 Network construction control method and medium applied to multiport optical storage integrated converter

Similar Documents

Publication Publication Date Title
CN110417055A (en) A kind of direct Power Control method inhibiting the fluctuation of photovoltaic combining inverter DC side busbar voltage
CN110011356A (en) A kind of control method for coordinating of the offer of PMSG blower primary frequency modulation and virtual inertia
CN110957763A (en) Two-stage type photovoltaic grid-connected power generation system and control method thereof
CN117096897A (en) Method for participating in grid frequency modulation support of two-stage type photovoltaic grid-connected power generation system
Xing et al. Research on the MPPT control simulation of wind and photovoltaic complementary power generation system
CN110336317B (en) Control method of photovoltaic grid-connected power generation system
Liu et al. A cost-efficient virtual synchronous generator system based on coordinated photovoltaic and supercapacitor
Sharma et al. Power quality and stability improvement of hybrid energy system under weak grid environment
Malla et al. Improvement of Power Quality through SMES Control in a Standalone Hybrid Microgrid System
Tian et al. Two-stage PV grid-connected control strategy based on adaptive virtual inertia and damping control for DC-link capacitor dynamics self-synchronization
Hua et al. Research on grid-connected control and simulation of microgrid inverter based on VSG
CN116914791A (en) Power flow logic control method based on hybrid energy storage system in micro-grid system
Babaei et al. Compensation of voltage sags and swells using photovoltaic source based DVR
Zhang et al. Analysis and design of a modified virtual synchronous generator control strategy for single-phase inverter application
CN115065068A (en) Virtual synchronous machine control method for photovoltaic system without energy storage configuration at source end
Brahma et al. Impact of system parameters on the performance of synchronverter
CN109842137B (en) Coordination control method for single-phase and three-phase series-parallel micro-grid group
Venkateswarlu et al. PV integrated Cuk converter for UPQC applications with power quality improvement using intelligent control techniques
Xu et al. A Power Oscillation Damping Algorithm of Distributed Generators Based on Optimized Second-order Virtual Inertia
Ray et al. Smart control strategy for a DC microgrid
Fletcher et al. Inverter Interfacing and Grid Behaviour
Papineni Modeling and simulation of battery and SMES-based DVR for grid-connected hybrid PV-wind power system with improved power quality features
Mokhtari et al. Behavior Analysis Of Asynchronous Wind Turbine In Presence Of Static Synchronous Compensator Operating With Fuzzy Logic Voltage Controller
Jefry et al. 51-level Multilevel Inverter Configuration for STATCOM Application
Thangam et al. SEPIC Converter with Closed Loop PI Controller for Grid Utilized PV System

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination