CN113517695A - Self-adaptive voltage current cooperative controller for improving electric energy quality of flexible micro-grid - Google Patents

Self-adaptive voltage current cooperative controller for improving electric energy quality of flexible micro-grid Download PDF

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CN113517695A
CN113517695A CN202110697727.XA CN202110697727A CN113517695A CN 113517695 A CN113517695 A CN 113517695A CN 202110697727 A CN202110697727 A CN 202110697727A CN 113517695 A CN113517695 A CN 113517695A
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current
voltage
frequency
distributed
power
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Inventor
何晋伟
徐科
郭培健
霍现旭
孙柏杨
李浩然
厉成元
徐晶
王利辉
姚程
余真
刘娟
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Tianjin Bindian Electric Power Engineering Co ltd
Tianjin University
State Grid Tianjin Electric Power Co Ltd
Electric Power Research Institute of State Grid Tianjin Electric Power Co Ltd
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Tianjin Bindian Electric Power Engineering Co ltd
Tianjin University
State Grid Tianjin Electric Power Co Ltd
Electric Power Research Institute of State Grid Tianjin Electric Power Co Ltd
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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
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • 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
    • H02J3/38—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
    • 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
    • H02J3/388—Islanding, i.e. disconnection of local power supply from the network
    • 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
    • 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
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics

Abstract

The invention relates to a self-adaptive voltage and current cooperative controller for improving the electric energy quality of a flexible microgrid, which is characterized in that an integral term is added in a power control loop in an interface converter of a traditional voltage and current cooperative controller, and a frequency self-adaptive voltage and current cooperative controller is constructed, so that a distributed power generation unit can well realize the harmonic compensation performance of a system under the condition of frequency change of the microgrid, and the power control precision of a distributed power generation unit set when the frequency disturbance occurs to the microgrid is improved. Due to the fact that a simple integral term is added in a traditional active power frequency control scheme, accurate power control of the controller under power grid voltage frequency disturbance is guaranteed. And by constructing the frequency self-adaptive voltage current cooperative controller, even if the frequency of harmonic distortion is influenced by the change of the fundamental frequency of the microgrid, the distributed generation unit set can accurately track the current.

Description

Self-adaptive voltage current cooperative controller for improving electric energy quality of flexible micro-grid
Technical Field
The invention belongs to the field of operation control of a power distribution network, and particularly relates to a self-adaptive voltage and current cooperative controller for improving the power quality of a flexible micro-grid.
Background
Distributed Generation (DG) units based on Renewable Energy (RES) are increasingly integrated into power distribution systems, the proportion of nonlinear loads in various loads is higher and higher, and meanwhile, harmonic pollution of the power distribution network can be caused by application of the nonlinear loads in the power grid. Power electronic converters with LCL filters are used as an effective interface between renewable energy sources and the grid, and interface converters typically have higher control bandwidths and can actively regulate the power quality of the distribution system without using any additional harmonic filtering devices.
The control schemes of the DG unit are divided into a Current Control Method (CCM) and a Voltage Control Method (VCM). The CCM adopts a robust control scheme, and can realize excellent harmonic compensation performance. However, when the distributed generator set is converted into independent island operation, CCM control has difficulty; the VCM is considered to be an effective solution applied to a dual-mode (when a micro-grid is connected with a network and frequency deviation occurs, the distributed generator set can achieve excellent system harmonic compensation control performance modes and island modes under different micro-grid frequency conditions by using the proposed frequency adaptive voltage current cooperative controller). In addition, the combination of DG virtual impedance and droop control further ensures load sharing among the DG units. However, it is difficult for a conventional VCM to adjust the harmonic current of a DG block line. Therefore, VCM is rarely used to solve the system harmonic problem.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provides a self-adaptive voltage and current cooperative controller for improving the power quality of a flexible micro-grid, utilizes the frequency self-adaptive voltage and current cooperative controller to replace a fixed frequency resonance controller in the traditional voltage and current cooperative control, and enables distributed power generation units to realize excellent system harmonic compensation control under different micro-grid frequency conditions when frequency deviation occurs in the micro-grid.
The technical problem to be solved by the invention is realized by adopting the following technical scheme:
the adaptive voltage and current cooperative controller for improving the power quality of the flexible microgrid comprises a microgrid circuit, an improved power control loop, an improved virtual impedance loop, a mode selection module and a frequency adaptive voltage and current cooperative controller, wherein the microgrid circuit is respectively connected with the improved power control loop and the frequency adaptive voltage and current cooperative controller, and the improved power control loop, the improved virtual impedance loop and the mode selection module are respectively connected with the frequency adaptive voltage and current cooperative controller.
Moreover, the microgrid circuit comprises: the distributed power generation unit is connected with the local load or is connected to the PCC of the distribution network or the microgrid through the LCL filter.
Furthermore, the improved power control loop is formed by the following mathematical model:
Figure 32019DEST_PATH_IMAGE001
Figure 847528DEST_PATH_IMAGE002
Figure 666580DEST_PATH_IMAGE003
wherein the content of the first and second substances,
Figure 491316DEST_PATH_IMAGE004
for the distributed power generating unit reference frequency,
Figure 94072DEST_PATH_IMAGE005
being the nominal frequency of the distributed power generating unit,
Figure 814903DEST_PATH_IMAGE006
for the droop coefficient of the real power control,
Figure 449147DEST_PATH_IMAGE007
is the rated active power output by the system,
Figure 421782DEST_PATH_IMAGE008
is the real-time active power output by the system,
Figure 254609DEST_PATH_IMAGE009
for the distributed generation unit reference voltage amplitude,
Figure 21708DEST_PATH_IMAGE010
for the distributed power generating unit nominal voltage,
Figure 205564DEST_PATH_IMAGE011
for reactive control, a droop coefficient and a gain coefficient of
Figure 981890DEST_PATH_IMAGE012
And
Figure 403645DEST_PATH_IMAGE013
，
Figure 607224DEST_PATH_IMAGE014
is the rated reactive power output by the system,
Figure 950481DEST_PATH_IMAGE015
is the real-time reactive power output by the system,
Figure 655131DEST_PATH_IMAGE016
in order to cut-off the frequency of the frequency,
Figure 337917DEST_PATH_IMAGE017
in order to filter the voltage of the capacitor,
Figure 837031DEST_PATH_IMAGE018
for the line current of a distributed power generating unit,
Figure 339688DEST_PATH_IMAGE019
to filter the capacitor voltageThe orthogonal components of (a) and (b),
Figure 582450DEST_PATH_IMAGE020
is the quadrature component of the distributed generation element line current.
Furthermore, the improved virtual impedance loop is formed by the following mathematical model:
Figure 854163DEST_PATH_IMAGE021
Figure 727441DEST_PATH_IMAGE022
wherein the content of the first and second substances,
Figure 842027DEST_PATH_IMAGE023
the virtual resistance generated for distributed generation unit control,
Figure 495338DEST_PATH_IMAGE024
for the distributed generation unit to control the virtual inductance generated,
Figure 11770DEST_PATH_IMAGE025
is a fundamental wave component extractor and is characterized in that,
Figure 993632DEST_PATH_IMAGE026
is composed of a fundamental wave component extractor
Figure 595515DEST_PATH_IMAGE027
The current of the fundamental wave is extracted,
Figure 55446DEST_PATH_IMAGE028
is a fundamental current
Figure 426385DEST_PATH_IMAGE029
By delaying the orthogonal component of
Figure 313569DEST_PATH_IMAGE030
The one-fourth period is obtained by the method,
Figure 340431DEST_PATH_IMAGE031
for the line current of a distributed power generating unit,
Figure 728687DEST_PATH_IMAGE032
is the nominal frequency of the distributed power generation unit.
Moreover, the mode selection module includes: a first selection mode, a second selection mode, a third selection mode and a fourth selection mode;
the first selection mode is as follows: when referring to the current
Figure 95078DEST_PATH_IMAGE033
Selected as local nonlinear load harmonic current
Figure 277797DEST_PATH_IMAGE034
The distributed power generation unit works in a local harmonic compensation mode and injects current of PCC
Figure 729638DEST_PATH_IMAGE035
Is sinusoidal;
the second selection mode is: when referring to the current
Figure 656006DEST_PATH_IMAGE036
When the harmonic suppression mode is set to zero, the distributed power generation unit works in a harmonic suppression mode, and the line current is at the moment
Figure 939220DEST_PATH_IMAGE037
Is a sinusoidal current;
the third selection mode is: when the input of the current control branch is from the reference current
Figure 433786DEST_PATH_IMAGE038
Line current
Figure 497557DEST_PATH_IMAGE039
Becomes a reference voltage
Figure 102982DEST_PATH_IMAGE040
Voltage of filter capacitor
Figure 37440DEST_PATH_IMAGE041
When the system switches to the conventional VCM mode;
the fourth selection mode is: obtaining harmonic voltage of PCC
Figure 30804DEST_PATH_IMAGE042
The reference current of the HCM is obtained as:
Figure 194588DEST_PATH_IMAGE043
wherein
Figure 462758DEST_PATH_IMAGE044
For the grid synthetic resistance, the distributed generation unit acts as a damping resistance at selected harmonic frequencies.
Moreover, the frequency-adaptive voltage-current cooperative controller is composed of the following mathematical model:
Figure 392668DEST_PATH_IMAGE045
wherein, the voltage control branch circuit
Figure 619250DEST_PATH_IMAGE046
The mathematical model of (a) is:
Figure 1821DEST_PATH_IMAGE047
；
current control branch
Figure 73682DEST_PATH_IMAGE048
The mathematical model of (a) is:
Figure 123677DEST_PATH_IMAGE049
；
active damping term
Figure 193265DEST_PATH_IMAGE050
The mathematical model of (a) is:
Figure 453345DEST_PATH_IMAGE051
；
wherein the content of the first and second substances,
Figure 938684DEST_PATH_IMAGE052
in order to control the reference value for the voltage,
Figure 967820DEST_PATH_IMAGE053
in order to filter the voltage of the capacitor,
Figure 145991DEST_PATH_IMAGE054
as a reference current, the current is,
Figure 893367DEST_PATH_IMAGE055
for the current in the output line on the converter side,
Figure 182397DEST_PATH_IMAGE056
in order to be able to supply the line current,
Figure 269302DEST_PATH_IMAGE057
for the fundamental frequency and the gain of the resonance adjuster,
Figure 743009DEST_PATH_IMAGE058
in order to be able to tune the bandwidth of the regulator,
Figure 587468DEST_PATH_IMAGE059
for the distributed power generating unit reference frequency,
Figure 539243DEST_PATH_IMAGE060
respectively, the gain of the resonant regulator, respectively,
Figure 680987DEST_PATH_IMAGE061
is the order of the harmonic wave,
Figure 60016DEST_PATH_IMAGE062
in order to control the proportional gain of the branch,
Figure 391771DEST_PATH_IMAGE063
is a scaling factor.
The invention has the advantages and positive effects that:
1. according to the invention, by adding the integral term in the power control loop in the interface converter of the traditional voltage-current cooperative controller and constructing the frequency self-adaptive voltage-current cooperative controller, the distributed power generation unit can well realize the system harmonic compensation performance under the condition of frequency change of the microgrid, and the power control precision of the distributed power generation unit set when the frequency disturbance occurs to the microgrid is improved.
2. The invention adopts an improved power control loop, and ensures the accurate power control of the controller under the voltage frequency disturbance of the power grid by adding a simple integral term in the traditional active power frequency control scheme.
3. According to the invention, by constructing the frequency self-adaptive voltage current cooperative controller, even if the frequency of harmonic distortion is influenced due to the change of the fundamental frequency of the microgrid, the distributed generation unit set can accurately track the current.
Drawings
FIG. 1 is a block diagram of the present invention
FIG. 2 is a block diagram of a controller for implementing frequency adaptive voltage current cooperative control by using second-order generalized integral;
FIG. 3 is a schematic diagram of an interface converter of a conventional voltage-current cooperative controller;
FIG. 4 is a waveform diagram of the control performance of the frequency adaptive voltage current cooperative controller operating in the harmonic non-control mode;
fig. 5 is a waveform diagram of the frequency adaptive voltage current cooperative controller control.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
The adaptive voltage and current cooperative controller for improving the power quality of the flexible microgrid is shown in fig. 1 and comprises a microgrid circuit, an improved power control loop, an improved virtual impedance loop, a mode selection module and a frequency adaptive voltage and current cooperative controller, wherein the microgrid circuit is respectively connected with the improved power control loop and the frequency adaptive voltage and current cooperative controller, and the improved power control loop, the improved virtual impedance loop and the mode selection module are respectively connected with the frequency adaptive voltage and current cooperative controller.
The microgrid circuit comprises: the distributed power generation unit is connected with the local load or is connected to the PCC of the distribution network or the microgrid through the LCL filter. In the embodiment, a single-phase distributed power generation unit is taken as an example for illustration, a direct current side of the distributed power generation unit converts direct current into alternating current through an inverter converter for output, and as the output is in a pulse form and contains more harmonic components, in order to reduce adverse effects of harmonic waves, an LCL filter is adopted for filtering output voltage; the LCL filter comprises a current transformer inductive reactance
Figure 147238DEST_PATH_IMAGE064
And
Figure 208735DEST_PATH_IMAGE065
1filter capacitor
Figure 899610DEST_PATH_IMAGE066
And net side inductive reactance
Figure 843295DEST_PATH_IMAGE067
And
Figure 12240DEST_PATH_IMAGE068
and thirdly, supplying the filtered alternating current to a local load or accessing the filtered alternating current to a power distribution network or a micro-grid through a point of common coupling PCC, wherein the embodiment of the invention represents a typical nonlinear local load by an uncontrolled diode rectification belt resistance load.
The conventional power control loop shown in fig. 3, but in grid-connected operation, the above conventional power control scheme can only achieve zero steady-state active power control error when the main grid frequency is fixed at a nominal value. In order to ensure accurate active power control under the voltage frequency disturbance of a power grid, a simple integral term is added in the traditional active power frequency control scheme of the improved power control loop, and a first-order low-pass filter is selected as a filter, and the improved power control loop is composed of the following mathematical models:
Figure 990560DEST_PATH_IMAGE069
Figure 852337DEST_PATH_IMAGE070
Figure 283318DEST_PATH_IMAGE071
wherein the content of the first and second substances,
Figure 583849DEST_PATH_IMAGE072
for the distributed power generating unit reference frequency,
Figure 26463DEST_PATH_IMAGE073
being the nominal frequency of the distributed power generating unit,
Figure 183775DEST_PATH_IMAGE074
for the droop coefficient of the real power control,
Figure 977419DEST_PATH_IMAGE075
is the rated active power output by the system,
Figure 878379DEST_PATH_IMAGE076
is the real-time active power output by the system,
Figure 441078DEST_PATH_IMAGE077
for the distributed generation unit reference voltage amplitude,
Figure 769291DEST_PATH_IMAGE078
for the distributed power generating unit nominal voltage,
Figure 112548DEST_PATH_IMAGE079
for reactive control, a droop coefficient and a gain coefficient of
Figure 683776DEST_PATH_IMAGE080
And
Figure 225616DEST_PATH_IMAGE081
，
Figure 600096DEST_PATH_IMAGE082
is the rated reactive power output by the system,
Figure 492966DEST_PATH_IMAGE083
is the real-time reactive power output by the system,
Figure 345515DEST_PATH_IMAGE084
in order to cut-off the frequency of the frequency,
Figure 7441DEST_PATH_IMAGE085
in order to filter the voltage of the capacitor,
Figure 552823DEST_PATH_IMAGE086
for the line current of a distributed power generating unit,
Figure 667409DEST_PATH_IMAGE087
being the quadrature component of the filter capacitor voltage,
Figure 651546DEST_PATH_IMAGE088
is the quadrature component of the distributed generation element line current.
The working process comprises the following steps:
step 1, capacitor in LCL filter in micro-grid circuit
Figure 43344DEST_PATH_IMAGE089
Sampling voltage and network side inductive reactance current to obtain filter capacitor voltage
Figure 884261DEST_PATH_IMAGE090
And line current of distributed generation unit
Figure 627089DEST_PATH_IMAGE091
And calculating real-time active power and reactive power output by the system.
Step 2, after the rated active power and reactive power output by the system are different from the real-time active power and reactive power, the difference is processed by a first-order low-pass filter
Figure 211654DEST_PATH_IMAGE092
And (4) filtering ripples in the actually measured real-time active power and reactive power.
And 3, according to the real-time active power and reactive power obtained through calculation, obtaining reference values of voltage amplitude and frequency by using active power frequency PI control and reactive power voltage amplitude PI control.
Step 4, reference frequency is obtained through distributed power generation units
Figure 457959DEST_PATH_IMAGE093
Calculating an angle
Figure 673040DEST_PATH_IMAGE094
By means of a reference generator
Figure 496639DEST_PATH_IMAGE095
Voltage drop across output virtual impedance
Figure 25841DEST_PATH_IMAGE096
。
The improvement of the virtual impedance loop is proposed to improve the adverse effects of the above-mentioned power control loop. The power control scheme of the scheme is based on the distributed power generation unit inductance feeder
Figure 251286DEST_PATH_IMAGE097
And
Figure 306442DEST_PATH_IMAGE098
is designed on the assumption that (1). To compensate for some of the effects of using output LCL filters in distributed generation units, the effects are typically reduced by controlling the interface converter to produce a virtual impedance. The improved virtual impedance loop is composed of the following mathematical models:
Figure 882917DEST_PATH_IMAGE099
Figure 12547DEST_PATH_IMAGE100
wherein the content of the first and second substances,
Figure 967864DEST_PATH_IMAGE101
the virtual resistance generated for distributed generation unit control,
Figure 587065DEST_PATH_IMAGE102
for the distributed generation unit to control the virtual inductance generated,
Figure 526202DEST_PATH_IMAGE103
is a fundamental wave component extractor and is characterized in that,
Figure 990681DEST_PATH_IMAGE104
is composed of a fundamental wave component extractor
Figure 66085DEST_PATH_IMAGE105
The current of the fundamental wave is extracted,
Figure 59448DEST_PATH_IMAGE106
is a fundamental current
Figure 79357DEST_PATH_IMAGE107
By delaying the orthogonal component of
Figure 488473DEST_PATH_IMAGE108
The one-fourth period is obtained by the method,
Figure 808596DEST_PATH_IMAGE109
is the line current of the distributed power generation unit.
Improving the virtual impedance loop to obtain a voltage control reference
Figure 379385DEST_PATH_IMAGE110
：
Figure 152169DEST_PATH_IMAGE111
。
The mode selection module comprises: a first selection mode, a second selection mode, a third selection mode and a fourth selection mode,
the first selection mode is as follows: when referring to the current
Figure 427293DEST_PATH_IMAGE112
Selected as local nonlinear load harmonic current
Figure 211709DEST_PATH_IMAGE113
The distributed power generation unit works in a local harmonic compensation mode and injects current of PCC
Figure 343613DEST_PATH_IMAGE114
Is sinusoidal.
The second selection mode is: when referring to the current
Figure 479060DEST_PATH_IMAGE115
When the harmonic suppression mode is set to zero, the distributed power generation unit works in a harmonic suppression mode, and the line current is at the moment
Figure 354612DEST_PATH_IMAGE116
Is a sinusoidal current.
The third selection mode is: when the input of the current control branch is from the reference current
Figure 587010DEST_PATH_IMAGE117
Line current
Figure 502532DEST_PATH_IMAGE118
Becomes a reference voltage
Figure 249908DEST_PATH_IMAGE119
Voltage of filter capacitor
Figure 538938DEST_PATH_IMAGE120
When the system switches to the conventional VCM mode; considering that the control objective in the harmonic non-control mode is to reduce the voltage distortion of the filter capacitor, the input of the current control branch can be simply set to
Figure 688160DEST_PATH_IMAGE121
。
When reference voltage is applied
Figure 771653DEST_PATH_IMAGE122
The ripple in (b) is regulated by a harmonic resonance controller in the current control branch. If the reference voltage is
Figure 944009DEST_PATH_IMAGE123
The disturbance increases, then the distributed generation unit voltage
Figure 161363DEST_PATH_IMAGE124
Large disturbances will also occur.
The invention adds a fourth selection mode as follows: obtaining harmonic voltage of PCC
Figure 774878DEST_PATH_IMAGE125
The reference current of the HCM is obtained as:
Figure 419486DEST_PATH_IMAGE126
the distributed power generation units act as damping resistors at selected harmonic frequencies, where the coefficient RVThe resistance is synthesized for the grid for determining the reference current in the HCM.
The constant-frequency voltage and current cooperative controller comprises a voltage control branch, a current control branch and an active damping item, and consists of three parallel control branches, wherein the expression is as follows:
Figure 16821DEST_PATH_IMAGE127
wherein the voltage control branch
Figure 772287DEST_PATH_IMAGE128
Closed-loop regulation and current control branch circuit for realizing fundamental wave capacitance voltage
Figure 505888DEST_PATH_IMAGE129
For regulating harmonic currents of DG lines, third term
Figure 524660DEST_PATH_IMAGE130
The detailed expression of the active damping term is as follows:
Figure 202766DEST_PATH_IMAGE131
the conventional constant-frequency voltage-current cooperative controller is designed to compensate for fixed-frequency harmonics in the microgrid, but when the fundamental frequency of the microgrid changes, the frequency of harmonic distortion is also affected. Once the harmonic frequency changes beyond the bandwidth of the corresponding resonant controller, the harmonic compensation performance will be affected. In order to ensure that the current can be accurately tracked under the condition of frequency disturbance, the invention provides a frequency self-adaptive voltage and current cooperative controller. Considering that the voltage of the distributed power generation unit must be synchronous with the voltage of the microgrid, namely the reference frequency of the system is always equal to the frequency of the microgrid in a steady state, the adaptive voltage current resonance controller is different from the constant-frequency voltage current resonance controller, and the reference frequency can be directly adopted in the adaptive voltage current resonance controller
Figure 637289DEST_PATH_IMAGE132
An adaptive voltage current resonance controller is constructed.
As shown in fig. 4, the frequency adaptive voltage-current cooperative controller is composed of the following mathematical model:
Figure 615610DEST_PATH_IMAGE133
wherein, the voltage control branch circuit
Figure 477386DEST_PATH_IMAGE134
The mathematical model of (a) is:
Figure 908368DEST_PATH_IMAGE135
；
current control branch
Figure 208899DEST_PATH_IMAGE136
The mathematical model of (a) is:
Figure 648583DEST_PATH_IMAGE137
；
active damping term
Figure 805895DEST_PATH_IMAGE138
The mathematical model of (a) is:
Figure 599539DEST_PATH_IMAGE139
。
finally, the distributed power generation unit interface converter is controlled by improving the power control loop and the frequency adaptive voltage current cooperative controller, the frequency dependence on the microgrid is low, partial low-pass and high-pass filters in the power controller and the virtual impedance loop can be removed, and the controller is further simplified.
The reference voltage of the power and virtual impedance control loop is regulated by a voltage control branch in a voltage-current coordinated controller, and with a fundamental frequency resonant controller, the ripple in the reference voltage will be regulated
Figure 500499DEST_PATH_IMAGE140
And automatically filtering. Due to this characteristic, it is possible to control the loop by setting in a virtual impedance
Figure 63198DEST_PATH_IMAGE141
And
Figure 594674DEST_PATH_IMAGE142
instead of the low pass filter in the reactive voltage amplitude control scheme and the fundamental frequency component extractor in the virtual impedance loop.
Fig. 4 is a waveform diagram showing the control performance of a controller using the proposed frequency adaptive voltage current. The waveform a is DG1 unit voltage, 250V/grid; the waveform b is DG2 unit voltage, 250V/grid; waveform c is the PCC voltage, 250V/grid. In the controller, the input of the current control branch is set to
Figure 734668DEST_PATH_IMAGE143
And the two distributed power generation units work in a harmonic uncontrollable mode, and a fundamental component extractor and a high-pass filter in the controller are removed at the same time. In the experiment, the voltages THD of the two groups of distributed generator sets are respectively 2.91% and 2.48%, and the expected effect can be achieved. Fig. 5 is a waveform diagram illustrating control performance using a modified power control loop and a frequency adaptive voltage current coordinated controller. The waveform a is DG unit active power, 100W/grid; the waveform b is DG set reactive power, 100 Var/grid; the waveform c is DG unit reference frequency disturbance, 0.5 Hz/grid; the waveform d is DG unit voltage, 250V/grid. It can be seen from the figure that when the voltage frequency of the power grid has certain disturbance, the method can avoid the protection of the distributed power generation unit set, improve the power control precision of the distributed power generation unit set when the frequency disturbance occurs to the microgrid, and the distributed power generation unit realizes good system harmonic compensation performance.
In conclusion, the frequency adaptive voltage and current cooperative controller provided by the invention can realize excellent system harmonic compensation performance when a DG unit is under different microgrid frequency conditions, and is a novel distributed microgrid harmonic compensation and power quality improvement control strategy which is worthy of popularization.
It should be emphasized that the embodiments described herein are illustrative rather than restrictive, and thus the present invention is not limited to the embodiments described in the detailed description, but also includes other embodiments that can be derived from the technical solutions of the present invention by those skilled in the art.

Claims (6)

1. Improve flexible little electric wire netting power quality's self-adaptation voltage electric current cooperative controller, its characterized in that: the frequency self-adaptive voltage and current cooperative controller comprises a micro-grid circuit, an improved power control loop, an improved virtual impedance loop, a mode selection module and a frequency self-adaptive voltage and current cooperative controller, wherein the micro-grid circuit is respectively connected with the improved power control loop and the frequency self-adaptive voltage and current cooperative controller, and the improved power control loop, the improved virtual impedance loop and the mode selection module are respectively connected with the frequency self-adaptive voltage and current cooperative controller.
2. The adaptive voltage and current cooperative controller for improving the power quality of the flexible microgrid according to claim 1, characterized in that: the microgrid circuit comprises: the distributed power generation unit is connected with the local load or is connected to the PCC of the distribution network or the microgrid through the LCL filter.
3. The adaptive voltage and current cooperative controller for improving the power quality of the flexible microgrid according to claim 1, characterized in that: the improved power control loop is composed of the following mathematical models:
Figure 613605DEST_PATH_IMAGE001
Figure 30811DEST_PATH_IMAGE002
Figure 529925DEST_PATH_IMAGE003
wherein the content of the first and second substances,
Figure 767002DEST_PATH_IMAGE004
for the distributed power generating unit reference frequency,
Figure 9765DEST_PATH_IMAGE005
being the nominal frequency of the distributed power generating unit,
Figure 547057DEST_PATH_IMAGE006
for the droop coefficient of the real power control,
Figure 217072DEST_PATH_IMAGE007
is the rated active power output by the system,
Figure 932657DEST_PATH_IMAGE008
is the real-time active power output by the system,
Figure 979110DEST_PATH_IMAGE009
for the distributed generation unit reference voltage amplitude,
Figure 370908DEST_PATH_IMAGE010
for the distributed power generating unit nominal voltage,
Figure 211825DEST_PATH_IMAGE011
for reactive control, a droop coefficient and a gain coefficient of
Figure 423495DEST_PATH_IMAGE012
And
Figure 273639DEST_PATH_IMAGE013
，
Figure 519944DEST_PATH_IMAGE014
rated reactive power output for the system，
Figure 531762DEST_PATH_IMAGE015
Is the real-time reactive power output by the system,
Figure 496307DEST_PATH_IMAGE016
in order to cut-off the frequency of the frequency,
Figure 822247DEST_PATH_IMAGE017
in order to filter the voltage of the capacitor,
Figure 313271DEST_PATH_IMAGE018
for the line current of a distributed power generating unit,
Figure 371357DEST_PATH_IMAGE019
being the quadrature component of the filter capacitor voltage,
Figure 682252DEST_PATH_IMAGE020
is the quadrature component of the distributed generation element line current.
4. The adaptive voltage and current cooperative controller for improving the power quality of the flexible microgrid according to claim 1, characterized in that: the improved virtual impedance loop is composed of the following mathematical models:
Figure 749565DEST_PATH_IMAGE021
Figure 95096DEST_PATH_IMAGE022
wherein the content of the first and second substances,
Figure 324083DEST_PATH_IMAGE023
the virtual resistance generated for distributed generation unit control,
Figure 325537DEST_PATH_IMAGE024
for the distributed generation unit to control the virtual inductance generated,
Figure 55596DEST_PATH_IMAGE025
is a fundamental wave component extractor and is characterized in that,
Figure 128070DEST_PATH_IMAGE026
is composed of a fundamental wave component extractor
Figure 652592DEST_PATH_IMAGE027
The current of the fundamental wave is extracted,
Figure 79025DEST_PATH_IMAGE028
is a fundamental current
Figure 612775DEST_PATH_IMAGE029
By delaying the orthogonal component of
Figure 870581DEST_PATH_IMAGE030
The one-fourth period is obtained by the method,
Figure 441370DEST_PATH_IMAGE031
for the line current of a distributed power generating unit,
Figure 214154DEST_PATH_IMAGE032
is the nominal frequency of the distributed power generation unit.
5. The adaptive voltage and current cooperative controller for improving the power quality of the flexible microgrid according to claim 1, characterized in that: the mode selection module comprises: a first selection mode, a second selection mode, a third selection mode and a fourth selection mode;
the first selection mode is as follows: when referring to the current
Figure 161382DEST_PATH_IMAGE033
Selected as local nonlinear load harmonic current
Figure 336011DEST_PATH_IMAGE034
The distributed power generation unit works in a local harmonic compensation mode and injects current of PCC
Figure 343281DEST_PATH_IMAGE035
Is sinusoidal;
the second selection mode is: when referring to the current
Figure 541045DEST_PATH_IMAGE036
When the harmonic suppression mode is set to zero, the distributed power generation unit works in a harmonic suppression mode, and the line current is at the moment
Figure 416597DEST_PATH_IMAGE037
Is a sinusoidal current;
the third selection mode is: when the input of the current control branch is from the reference current
Figure 55520DEST_PATH_IMAGE038
Line current
Figure 358325DEST_PATH_IMAGE039
Becomes a reference voltage
Figure 715488DEST_PATH_IMAGE040
Voltage of filter capacitor
Figure 394731DEST_PATH_IMAGE041
When the system switches to the conventional VCM mode;
the fourth selection mode is: obtaining harmonic voltage of PCC
Figure 153740DEST_PATH_IMAGE042
The reference current of the HCM is obtained as:
Figure 627446DEST_PATH_IMAGE043
wherein
Figure 474835DEST_PATH_IMAGE044
For the grid synthetic resistance, the distributed generation unit acts as a damping resistance at selected harmonic frequencies.
6. The adaptive voltage and current cooperative controller for improving the power quality of the flexible microgrid according to claim 1, characterized in that: the frequency adaptive voltage current cooperative controller is composed of the following mathematical models:
Figure 895452DEST_PATH_IMAGE045
wherein, the voltage control branch circuit
Figure 633601DEST_PATH_IMAGE046
The mathematical model of (a) is:
Figure 153575DEST_PATH_IMAGE047
；
current control branch
Figure 609964DEST_PATH_IMAGE048
The mathematical model of (a) is:
Figure 506376DEST_PATH_IMAGE049
；
active damping term
Figure 364611DEST_PATH_IMAGE050
The mathematical model of (a) is:
Figure 789907DEST_PATH_IMAGE051
；
wherein the content of the first and second substances,
Figure 936855DEST_PATH_IMAGE052
in order to control the reference value for the voltage,
Figure 496012DEST_PATH_IMAGE053
in order to filter the voltage of the capacitor,
Figure 84119DEST_PATH_IMAGE054
as a reference current, the current is,
Figure 336109DEST_PATH_IMAGE055
for the current in the output line on the converter side,
Figure 376877DEST_PATH_IMAGE056
in order to be able to supply the line current,
Figure 474146DEST_PATH_IMAGE057
for the fundamental frequency and the gain of the resonance adjuster,
Figure 510235DEST_PATH_IMAGE058
in order to be able to tune the bandwidth of the regulator,
Figure 542914DEST_PATH_IMAGE059
for the distributed power generating unit reference frequency,
Figure 195612DEST_PATH_IMAGE060
respectively, the gain of the resonant regulator, respectively,
Figure 237517DEST_PATH_IMAGE061
is the order of the harmonic wave,
Figure 924850DEST_PATH_IMAGE062
in order to control the proportional gain of the branch,
Figure 456326DEST_PATH_IMAGE063
is in proportionAnd (4) the coefficient.
CN202110697727.XA 2021-06-23 2021-06-23 Self-adaptive voltage current cooperative controller for improving electric energy quality of flexible micro-grid Pending CN113517695A (en)

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CN102163843A (en) * 2010-02-19 2011-08-24 Abb研究有限公司 Control method for single-phase grid-connected LCL inverter
CN107863785A (en) * 2017-12-13 2018-03-30 山东大学 The micro-capacitance sensor seamless switching control system and method for voltage x current Collaborative Control
CN110429601A (en) * 2019-08-27 2019-11-08 内蒙古电力(集团)有限责任公司内蒙古电力科学研究院分公司 A kind of isolated island micro-capacitance sensor PCC node voltage increased quality method

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CN102163843A (en) * 2010-02-19 2011-08-24 Abb研究有限公司 Control method for single-phase grid-connected LCL inverter
CN107863785A (en) * 2017-12-13 2018-03-30 山东大学 The micro-capacitance sensor seamless switching control system and method for voltage x current Collaborative Control
CN110429601A (en) * 2019-08-27 2019-11-08 内蒙古电力(集团)有限责任公司内蒙古电力科学研究院分公司 A kind of isolated island micro-capacitance sensor PCC node voltage increased quality method

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