CN115483713B - Output impedance correction method and system based on voltage feedforward channel under weak current network - Google Patents
Output impedance correction method and system based on voltage feedforward channel under weak current network Download PDFInfo
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/40—Synchronising a generator for connection to a network or to another generator
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- H—ELECTRICITY
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- 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
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Abstract
The embodiment of the invention discloses a correction method and a correction system for output impedance based on a voltage feedforward channel under a weak current network. The method comprises the following steps: determining the cross frequency according to the amplitude-frequency curve of the output impedance of the inverter and the amplitude-frequency curve of the power grid impedance of the grid-connected inverter system; the grid-connected inverter system comprises an inverter end and a power grid end; determining the phase lifted by the output impedance according to the current phase margin of the grid-connected inverter system; and adjusting and optimizing a voltage feedforward transfer function of the grid-connected inverter system according to the crossover frequency and the phase, thereby achieving the purpose of correcting the output impedance. The invention not only can improve the stability margin of the grid-connected inverter system by correcting the output impedance of the inverter, but also reduces the complexity of correcting the output impedance and the difficulty of developing an embedded system.
Description
Technical Field
The invention relates to the technical field of new energy grid connection, in particular to a method and a system for correcting output impedance based on a voltage feedforward channel under a weak current network.
Background
The large-scale new energy power station is mostly located at the tail end of a power grid where the novel power system is located, the distance from the power load is far, the strength of the power grid is weak, the power grid is equivalent to the increase of impedance between the inverter end and the infinite power grid, the stability margin of the grid-connected inverter system is reduced, and the stability is seriously affected. Currently, for a dual closed control loop of a conventional grid-connected inverter, output impedance correction may be applied to the current loop forward path and the voltage feed-through path.
For example, the literature "grid-tie inverter impedance phase remodeling control with novel PLL structure under weak current network" (gaku, xifan, jiang Fei, guo Qi, lu Baihua, [ J ]. Chinese motor engineering journal, 2020,40 (20): 12.) introduces an advanced correction link at the current loop forward path that improves the system stability margin by increasing the phase of the output impedance at the frequency of the cross-section without substantially changing the amplitude of the output impedance at the frequency of the cross-section, but that reduces the low-band current loop gain, resulting in an increased static error of the current control.
For example, the literature on the basis of impedance analysis method for researching dynamic interaction effect of photovoltaic grid-connected inverter and power grid (Chen Xin, zhang, wangcheng [ J ]. Chinese motor engineering report, 2014,34 (27): 9 ]), the literature on the method for reconstructing impedance of optical storage micro-grid converter and stability analysis (Yang Ling [ D ]. Hunan university.2019 ]), and the Chinese patent No. CN 110148943A all introduce a correction link of output impedance at the voltage feed-forward channel of the inverter end, but have the following problems:
(1) The voltage feedforward transfer function for output impedance correction has complex forms, such as second-order and above differential forms, so that the development and application possibility of the embedded system is greatly reduced;
(2) Before the output impedance of the feed-forward channel is introduced for correction, the voltage feed-forward transfer function is 0, namely no voltage feed-forward exists, and larger deviation is caused between the voltage feed-forward transfer function and the actual inverter application;
(3) The computation delay in the control loop and the modulation delay caused by the zero-order retainer are ignored, so that a large deviation is generated in the modeling process. After taking control delays into account, a superphysical link will occur in the transfer function based on the feedforward path output impedance correction.
Therefore, how to improve the stability margin of the grid-connected inverter system by correcting the output impedance of the inverter on the premise of reducing the complexity of the correction of the output impedance and the difficulty of the development of the embedded system is a technical problem to be solved at present.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a correction method and a correction system for the output impedance based on a voltage feedforward channel under a weak current network, which not only can improve the stability margin of a grid-connected inverter system by correcting the output impedance of an inverter, but also can reduce the complexity of correcting the output impedance and the development difficulty of an embedded system.
In a first aspect, an embodiment of the present invention provides a method for correcting output impedance based on a voltage feedforward channel in a weak current network, including:
determining the cross frequency according to the amplitude-frequency curve of the output impedance of the inverter and the amplitude-frequency curve of the power grid impedance of the grid-connected inverter system; the grid-connected inverter system comprises an inverter end and a power grid end;
determining the phase of the output impedance to be lifted according to the current phase margin of the grid-connected inverter system;
and adjusting and optimizing a voltage feedforward transfer function of the grid-connected inverter system according to the crossover frequency and the phase so as to correct the output impedance.
Preferably, in the method for correcting the output impedance based on the voltage feedforward channel under the weak current network, before determining the cross frequency according to the amplitude-frequency curve of the output impedance of the inverter and the amplitude-frequency curve of the grid impedance of the grid-connected inverter system, the method further includes:
an equivalent circuit of the grid-connected inverter system is built, and an output impedance model and a power grid impedance model are built based on the equivalent circuit;
and generating an amplitude-frequency curve of the output impedance and an amplitude-frequency curve of the power grid impedance according to the output impedance model and the power grid impedance model respectively.
More preferably, in the method for correcting output impedance of a voltage feedforward channel under a weak current network, the establishing the output impedance model and the power grid impedance model based on the equivalent circuit includes:
constructing the power grid impedance model according to the equivalent resistance and the equivalent inductance of the power grid impedance in the equivalent circuit;
and constructing the output impedance model according to the parameter information of the inverter, the voltage feedforward transfer function and the transfer function of the current loop controller.
More preferably, in the method for correcting output impedance based on a voltage feedforward channel under a weak current network, the constructing the output impedance model according to parameter information of the inverter, the voltage feedforward transfer function, and a transfer function of a current loop controller includes:
acquiring a control delay function of the inverter;
and constructing the output impedance model according to the control delay function, the parameter information of the inverter, the voltage feedforward transfer function and the transfer function of the current loop controller.
More preferably, in the correction method based on the output impedance of the voltage feedforward channel under the weak current network, the expression of the control delay function is:
wherein s=jω, j 2 = -1, ω is angular frequency, T s Is the sampling period.
Preferably, in the method for correcting the output impedance based on the voltage feedforward channel under the weak current network, the inverter end comprises a current source and output impedance, and the network end comprises an ideal voltage source and network impedance;
the current source and the output impedance are connected in parallel to form the inverter end, and the ideal voltage source and the power grid impedance are connected in series to form the power grid end.
Preferably, in the method for correcting the output impedance based on the voltage feedforward channel under the weak power grid, before determining the phase of the output impedance to be boosted according to the current phase margin of the grid-connected inverter system, the method further includes:
and determining the phase margin of the grid-connected inverter system at present according to the amplitude-frequency curve of the output impedance and the amplitude-frequency curve of the power grid impedance.
Preferably, in the method for correcting the output impedance based on the voltage feedforward channel under the weak current network, the expression of the optimized voltage feedforward transfer function is:
wherein k is 1 、k 2 K 3 The expressions of (2) are respectively:
wherein G is f (s) is a voltage feedforward transfer function, G' f (s) is a tuned voltage feedforward transfer function, alpha is a constant between 0 and 1, s=jω, j 2 = -1, ω is angular frequency, T s In order to sample the period of time,is the phase.
Preferably, in the method for correcting the output impedance based on the voltage feedforward channel under the weak current network, the inverter is any one of a photovoltaic inverter, a wind power converter and an energy storage converter.
In a second aspect, an embodiment of the present invention further provides a correction system for output impedance based on a voltage feedforward channel under a weak current network, including:
the first determining module is used for determining the cross frequency according to the amplitude-frequency curve of the output impedance of the inverter and the amplitude-frequency curve of the power grid impedance of the grid-connected inverter system; the grid-connected inverter system comprises an inverter end and a power grid end;
the second determining module is used for determining the phase of the output impedance to be lifted according to the phase margin of the grid-connected inverter system at present;
and the correction module is used for optimizing the voltage feedforward transfer function of the grid-connected inverter system according to the crossover frequency and the phase so as to correct the output impedance.
According to the correction method and system for the output impedance based on the voltage feedforward channel under the weak current network, the cross frequency is determined through the amplitude-frequency curve of the output impedance of the inverter and the amplitude-frequency curve of the power grid impedance of the grid-connected inverter system, the phase to be lifted of the output impedance is determined according to the phase margin of the current grid-connected inverter system, and then the voltage feedforward transfer function is optimized according to the cross frequency and the phase, so that the purpose of correcting the output impedance is achieved. On the premise of lower crossover frequency based on a weak current network, the phase and crossover frequency of the output impedance to be improved are determined, and the voltage feedforward transfer function is optimized, so that the correction of the output impedance is realized, the stability margin of a grid-connected inverter system can be improved by correcting the output impedance of the inverter, and the complexity of correcting the output impedance and the difficulty of developing an embedded system are reduced.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a flow chart of a method for correcting output impedance based on a voltage feedforward channel under a weak current network according to an embodiment of the present invention;
fig. 2 is a control block diagram of an LC-type grid-connected inverter in a correction method based on output impedance of a voltage feedforward channel under a weak current network according to an embodiment of the present invention;
FIG. 3 is a flow chart of a method for correcting output impedance based on a voltage feedforward channel under a weak current network according to an embodiment of the present invention;
fig. 4 is a schematic diagram of an equivalent circuit of a grid-connected inverter system in a correction method based on output impedance of a voltage feedforward channel under a weak current network according to an embodiment of the present invention;
FIG. 5 is another flow chart of a method for correcting output impedance based on a voltage feedforward channel in a weak current network according to an embodiment of the present invention;
fig. 6 is a topological diagram of a new energy three-phase grid-connected inverter in a correction method based on output impedance of a voltage feedforward channel under a weak current network provided by the embodiment of the invention;
FIG. 7 is another flow chart of a method for correcting output impedance based on a voltage feedforward channel in a weak current network according to an embodiment of the present invention;
fig. 8 is a baud chart of output impedance after output impedance correction and grid impedance in the correction method based on output impedance of a voltage feedforward channel under a weak grid provided by the embodiment of the invention;
fig. 9 is a schematic block diagram of a correction system based on output impedance of a voltage feedforward channel under a weak current network according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be understood that the terms "comprises" and "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It is also to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in this specification and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
It should be further understood that the term "and/or" as used in the present specification and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes such combinations.
Referring to fig. 1, fig. 1 is a flowchart illustrating a method for correcting output impedance based on a voltage feedforward channel in a weak current network according to an embodiment of the present invention.
As shown in fig. 1, the method includes steps S110 to S130.
S110, determining a cross frequency according to an amplitude-frequency curve of the output impedance of the inverter and an amplitude-frequency curve of the power grid impedance of the grid-connected inverter system; the grid-connected inverter system comprises an inverter end and a grid end.
Specifically, the grid-connected inverter system comprises an inverter end and a power grid end, the crossover frequency is the frequency of the boundary point of the amplitude-frequency curve of the output impedance and the amplitude-frequency curve of the power grid impedance, and the crossover frequency can be obtained through the frequency corresponding to the intersection point of the amplitude-frequency curve in the baud diagram where the power grid impedance and the output impedance are located.
The output impedance of the inverter is mainly affected by the control loop and the form of the filter, and the filter is not limited to the LC filter, but may be a single L filter, an LCL filter, or other types of filters. Meanwhile, the inverter can be any one of a photovoltaic inverter, a wind power converter and an energy storage converter, and is not limited to a three-phase inverter and is not limited to the type of the three-phase inverter.
For a grid-connected inverter of an LC-type filter, reference can be made to fig. 2, wherein in the control diagram shown in fig. 2, L 1 Is the filter inductance, C is the filter capacitance, Z g For the impedance of the power grid, the current loop adopts inverter current feedback control, i ref Is the current reference value, i 1 For the filter inductor current, i g To get in the network current, V g For the grid voltage, V PCC For inverter port voltage, G i (s) is the transfer function of the current controller, G f (s) is the voltage feedforward transfer function of the grid-connected inverter system, which is generally proportional feedforward, G d And(s) is control delay.
In another embodiment, as shown in fig. 3, step S210 and step S220 are further included before step S110.
S210, constructing an equivalent circuit of the grid-connected inverter system, and establishing an output impedance model and a power grid impedance model based on the equivalent circuit;
s220, generating an amplitude-frequency curve of the output impedance and an amplitude-frequency curve of the power grid impedance according to the output impedance model and the power grid impedance model respectively.
In this embodiment, the equivalent circuit of the grid-connected inverter system may be simplified by the LC-type grid-connected inverter control block diagram shown in fig. 2 to obtain the equivalent circuit shown in fig. 4, where the equivalent circuit may be used as the equivalent circuit of the grid-connected inverter system mentioned in the embodiment of the present application, that is, the inverter end in the grid-connected inverter system is formed by parallel connection of a current source and an output impedance, and the grid end is formed by series connection of an ideal voltage source and a grid impedance. The expression of the network access current of the inverter can be:
wherein i is g For the current of the incoming network s=jω, j 2 = -1, ω is angular frequency, i s Is a current source Z 0 Z is the output impedance g For the impedance of the electric network, V g Is an ideal voltage source.
In another embodiment, as shown in fig. 5, step S210 includes steps S211 and S212.
S211, constructing the power grid impedance model according to the equivalent resistance and the equivalent inductance of the power grid impedance in the equivalent circuit;
s212, constructing the output impedance model according to the parameter information of the inverter, the voltage feedforward transfer function and the transfer function of the current loop controller.
In this embodiment, the equivalent resistance and the equivalent inductance of the grid impedance may be calculated according to an equivalent circuit corresponding to the grid end of the grid-connected inverter system. In the embodiment of the application, the inverter end may include a direct current power supply, a three-phase inverter and an LC filter, and the three-phase inverter may be a photovoltaic grid-connected inverter. The power grid impedance model can be constructed by referring to the topological graph of the energy three-phase grid-connected inverter provided by fig. 6, and the power grid impedance model can be constructed by acquiring the equivalent resistance and the equivalent inductance of the power grid impedance from fig. 6. The expression corresponding to the power grid impedance model may be:
Z g (s)＝R g +sL g
wherein Z is g For the impedance of the electric network, R g Is the equivalent resistance of the power grid impedance, L g Is the equivalent inductance of the grid impedance.
In addition, the characteristic of low crossover frequency under the weak current network is considered, and meanwhile, the filter capacitor mainly influences the high frequency of the output impedance, so that the effect of the related term of the filter capacitor in the denominator of the expression corresponding to the output impedance model can be ignored under the condition of small error, and the development difficulty of the embedded system can be further reduced.
In another embodiment, as shown in fig. 7, step S212 includes steps S2121 and S2122.
S2121, acquiring a control delay function of the inverter;
s2122, constructing the output impedance model according to the control delay function, the parameter information of the inverter, the voltage feedforward transfer function and the transfer function of the current loop controller.
The control delay function in this embodiment may be obtained based on the control theory of the control block diagram shown in fig. 2, where the expression of the control delay function may be:
wherein G is d To control the delay, s=jω, j 2 = -1, ω is angular frequency, T s Is the sampling period.
Specifically, in the above expression for controlling delay, the calculated delay may be T s The zero-order keeper has a delay of 0.5T s So that the total calculated delay is 1.5T s And obtaining the expression for controlling the delay. According to the embodiment of the application, the influence of control delay in the output impedance is considered, and the realization method of the super physical link for counteracting the control delay is provided, so that the accuracy of the expression corresponding to the impedance model can be further improved. Taking a photovoltaic grid-connected inverter as an example, the parameter information of the inverter comprises an inverter filter inductor, an inverter filter capacitor and fundamental wave frequency. The expression corresponding to the output impedance model may be:
wherein Z is 0 (s) is the output impedance after adding control delay, L 1 Is the filter inductance, C is the filter capacitance, G i (s) is the transfer function of the current loop controller, G f (s) is a voltage feedforward transfer function, s=jω, j 2 = -1, ω is angular frequency, G d To control the delay.
In addition, the current loop controller may employ a PI controller, where the transfer function of the current loop controller has the following expression:
wherein the parameter k p May be 0.452, parameter k i May be 98.2.
It should be noted that the current loop controller is not limited to the PI controller, but may be other current loop controllers such as PR controller.
S120, determining the phase of the output impedance to be lifted according to the phase margin of the grid-connected inverter system.
The method and the device are mainly used for correcting the output impedance of the grid-connected inverter system to improve the stability margin of the grid-connected inverter system. Since the increase of the grid impedance of the grid-connected inverter system can reduce the stability margin of the grid-connected inverter system, in order to ensure that the grid-connected inverter system has enough stability, a proper phase is required to be selected to meet the condition that the phase margin of the grid-connected inverter system is larger than 30 degrees. The stability margin is used for measuring whether the system is stable or not, the stability margin comprises a gain margin and a phase margin, the stability margin can be used for representing whether the system is stable or not through the gain margin and the phase margin, the phase margin can be regarded as phase change which can be increased before the system enters an unstable state, and the larger the phase margin is, the more stable the system is, namely the larger the phase margin is when the stability margin of the grid-connected inverter system is more stable.
Specifically, when the stability margin of the grid-connected inverter system is poor, the current phase margin of the grid-connected inverter system is not necessarily greater than 30 degrees, at this time, the phase of the output impedance to be improved is required to be determined according to the current phase margin, and the voltage feedforward transfer function is improved through the selected phase and the crossover frequency so as to realize the correction of the output impedance, thereby realizing the improvement of the stability margin of the grid-connected inverter system.
In another embodiment, before step S120, the method further includes the steps of: and determining the phase margin of the grid-connected inverter system at present according to the amplitude-frequency curve of the output impedance and the amplitude-frequency curve of the power grid impedance.
Specifically, the amplitude-frequency curve of the output impedance and the amplitude-frequency curve of the power grid impedance both have respective baud diagrams, and the phase margin of the current grid-connected system can be determined through the baud diagrams of the respective amplitude-frequency curves. The expression of the phase margin of the grid-connected inverter system may be:
PM＝180°-[∠Z g (j2πf c )-∠Z o (j2πf c )]
wherein PM is a phase margin, f c For crossover frequency j 2 ＝-1，Z g For the impedance of the electric network, Z 0 Is the output impedance.
And S130, adjusting and optimizing a voltage feedforward transfer function of the grid-connected inverter system according to the crossover frequency and the phase so as to correct the output impedance.
Specifically, in the double closed loop control loop of the grid-connected inverter, output impedance correction can be achieved through the voltage feedforward channel, in the embodiment, the voltage feedforward transfer function is adjusted through the crossover frequency and the phase to generate the adjusted voltage feedforward transfer function, the stability margin of the grid-connected inverter system can be improved through correction of the output impedance of the inverter, and the complexity of correction of the output impedance and the difficulty of development of the embedded system are reduced. The expression of the adjusted voltage feedforward transfer function may be:
wherein k is 1 、k 2 K 3 The expressions of (2) are respectively:
wherein G is f (s) is a voltage feedforward transfer function, G' f (s) is a tuned voltage feedforward transfer function, alpha is a constant between 0 and 1, s=jω, j 2 = -1, ω is angular frequency, T s In order to sample the period of time,is the phase.
The expression corresponding to the output impedance model generated by the tuned voltage feedforward transfer function may be:
wherein Z' 0 For the output impedance generated by the tuned voltage feed-forward transfer function, L 1 Is the filter inductance, C is the filter capacitance, G i (s) is the transfer function of the current loop controller, s=jω, j 2 = -1, ω is angular frequency, G d To control the delay.
Taking a photovoltaic inverter as an example, the topology of the grid-connected inverter system is shown in fig. 6, the parameter information of the photovoltaic grid-connected inverter comprises an inverter filter inductor, an inverter filter capacitor and a fundamental frequency, wherein the inverter filter inductor can be 120 mu H, the inverter filter capacitor can be 34 mu F, the fundamental frequency can be 50Hz, the equivalent inductance and the equivalent resistance of the power grid impedance can be 5.3mH and 0.1 omega respectively, and an original control loop adopts a voltage feedforward proportionality coefficient, namely G f (s) may be 0.95, parameter k in the transfer function of the current loop controller p 、k i The sampling period may be 55.56 mus and the crossover frequency may be derived from the baud plot of the output impedance and the grid impedance before the output impedance is uncorrected, which may be 160Hz, respectively, 0.452, 98.2.
When the output impedance is uncorrected, the stability margin of the grid-connected inverter system is about 13.4 °, i.e. the stability margin is low. When the output impedance correction method is adopted, if the target phase is increased to 30 DEG, the parameter k can be calculated 1 、k 2 、k 3 Taking α=0.1, the output impedance corrected baud chart can refer to fig. 8, where fig. 8 is a baud chart of the output impedance corrected by the output impedance correction method based on the voltage feedforward channel in the weak current network according to the embodiment of the present invention, where the upper part in fig. 8 is an amplitude-frequency curve of the output impedance and the power network impedance, and the lower part in fig. 8 is a phase-frequency characteristic curve of the output impedance and the power network impedance. As can be seen from fig. 8, the amplitude of the output impedance at the crossover frequency is almost unchanged, but the phase margin of the grid-connected inverter system is increased to 34.6 °, at which point the phase margin meets the demand.
In addition, the filter capacitance is ignored due to the voltage feedforward transfer functionThe effect of (2) and the approximation of the super-physical link cause a certain error in the phase rise, but within an acceptable range, if the phase is further increasedThe phase margin can be further improved.
In the correction method of the output impedance based on the voltage feedforward channel under the weak current network provided by the embodiment of the invention, the cross frequency is determined according to the amplitude-frequency curve of the output impedance of the inverter and the amplitude-frequency curve of the power grid impedance of the grid-connected inverter system; the grid-connected inverter system comprises an inverter end and a power grid end; determining the phase lifted by the output impedance according to the current phase margin of the grid-connected inverter system; and adjusting and optimizing a voltage feedforward transfer function of the grid-connected inverter system according to the crossover frequency and the phase so as to achieve the purpose of correcting the output impedance. The method not only can improve the stability margin of the grid-connected inverter system by correcting the output impedance of the inverter, but also reduces the complexity of correcting the output impedance and the difficulty of developing an embedded system.
The embodiment of the invention also provides a correction system based on the output impedance of the voltage feedforward channel under the weak current network, which is used for executing any embodiment of the correction method based on the output impedance of the voltage feedforward channel under the weak current network.
Specifically, referring to fig. 9, fig. 9 is a schematic block diagram of a correction system based on an output impedance of a voltage feedforward channel in a weak current network according to an embodiment of the present invention.
As shown in fig. 9, the correction system based on the output impedance of the voltage feedforward channel under the weak current network includes a first determination module 110, a second determination module 120, and a correction module 130.
A first determining module 110, configured to determine a cross frequency according to an amplitude-frequency curve of an output impedance of the inverter and an amplitude-frequency curve of a grid impedance of the grid-connected inverter system; the grid-connected inverter system comprises an inverter end and a power grid end; a second determining module 120, configured to determine a phase of the output impedance to be boosted according to a phase margin of the current grid-connected inverter system; and the correction module 130 is configured to tune a voltage feedforward transfer function of the grid-connected inverter system according to the crossover frequency and the phase to correct the output impedance.
In other embodiments of the invention, the correction system based on the output impedance of the voltage feedforward channel under the weak current network further includes: a first building module and a first generating module.
The first construction module is used for constructing an equivalent circuit of the grid-connected inverter system and establishing an output impedance model and a power grid impedance model based on the equivalent circuit; the first generation module is used for generating an amplitude-frequency curve of the output impedance and an amplitude-frequency curve of the power grid impedance according to the output impedance model and the power grid impedance model respectively.
In other inventive embodiments, the first building block comprises: a second build module and a third build module.
The second construction module is used for constructing the power grid impedance model according to the equivalent resistance and the equivalent inductance of the power grid impedance in the equivalent circuit; and the third construction module is used for constructing the output impedance model according to the parameter information of the inverter, the voltage feedforward transfer function and the transfer function of the current loop controller.
In other inventive embodiments, the third building block comprises: an acquisition module and a fourth construction module.
The acquisition module is used for acquiring a control delay function of the inverter;
and the second generation module is used for constructing the output impedance model according to the control delay function, the parameter information of the inverter, the voltage feedforward transfer function and the transfer function of the current loop controller.
In other embodiments of the invention, the correction system based on the output impedance of the voltage feedforward channel under the weak current network further includes: and a third determination module.
And the third determining module is used for determining the current phase margin of the grid-connected inverter system according to the amplitude-frequency curve of the output impedance and the amplitude-frequency curve of the power grid impedance.
It will be clear to those skilled in the art that, for convenience and brevity of description, specific working procedures of the above-described system and module may refer to corresponding procedures in the foregoing method embodiments, which are not described herein again.
The steps in the method of the embodiment of the application can be sequentially adjusted, combined and deleted according to actual needs.
The modules in the system of the embodiment of the application can be combined, divided and pruned according to actual needs.
In addition, each functional module in each embodiment of the present application may be integrated into one processing module, or each module may exist alone physically, or two or more modules may be integrated into one module. The integrated modules may be implemented in hardware or in software functional units.
While the invention has been described with reference to certain preferred embodiments, it will be understood by those skilled in the art that various changes and substitutions of equivalents may be made and equivalents will be apparent to those skilled in the art without departing from the scope of the invention. Therefore, the protection scope of the invention is subject to the protection scope of the claims.
Claims (10)
1. The method for correcting the output impedance based on the voltage feedforward channel under the weak current network is characterized by comprising the following steps:
determining the cross frequency according to the amplitude-frequency curve of the output impedance of the inverter and the amplitude-frequency curve of the power grid impedance of the grid-connected inverter system; the grid-connected inverter system comprises an inverter end and a power grid end;
determining the phase of the output impedance to be lifted according to the current phase margin of the grid-connected inverter system;
generating a regulated voltage feedforward transfer function according to the crossover frequency, the phase and the voltage feedforward transfer function of the grid-connected inverter system, and generating a corrected output impedance according to the regulated voltage feedforward transfer function so as to realize correction of the output impedance.
2. The method for correcting output impedance based on voltage feedforward path under weak current network according to claim 1, further comprising, before determining the frequency of the cross-over according to the frequency curve of the output impedance of the inverter and the frequency curve of the grid impedance of the grid-connected inverter system:
an equivalent circuit of the grid-connected inverter system is built, and an output impedance model and a power grid impedance model are built based on the equivalent circuit;
and generating an amplitude-frequency curve of the output impedance and an amplitude-frequency curve of the power grid impedance according to the output impedance model and the power grid impedance model respectively.
3. The method for correcting the output impedance of the weak current network based on the voltage feedforward channel according to claim 2, wherein the establishing the output impedance model and the grid impedance model based on the equivalent circuit includes:
constructing the power grid impedance model according to the equivalent resistance and the equivalent inductance of the power grid impedance in the equivalent circuit;
and constructing the output impedance model according to the parameter information of the inverter, the voltage feedforward transfer function and the transfer function of a current loop controller in the grid-connected inverter system.
4. The method for correcting output impedance based on voltage feedforward channel under weak current network according to claim 3, wherein said constructing the output impedance model according to the parameter information of the inverter, the voltage feedforward transfer function, and the transfer function of the current loop controller comprises:
acquiring a control delay function of the inverter;
and constructing the output impedance model according to the control delay function, the parameter information of the inverter, the voltage feedforward transfer function and the transfer function of the current loop controller.
5. The method for correcting output impedance based on voltage feedforward path in weak current network according to claim 4, wherein said control delay function has the expression:
wherein s=jω, j 2 = -1, ω is angular frequency, T s Is the sampling period.
6. The method for correcting output impedance based on voltage feedforward path under weak current network according to claim 1, wherein the inverter side includes current source and output impedance, and the grid side includes ideal voltage source and grid impedance;
the current source and the output impedance are connected in parallel to form the inverter end, and the ideal voltage source and the power grid impedance are connected in series to form the power grid end.
7. The method for correcting an output impedance based on a voltage feedforward path under a weak current network according to claim 1, further comprising, before said determining a phase of the output impedance to be boosted according to a phase margin of the current grid-connected inverter system:
and determining the phase margin of the grid-connected inverter system at present according to the amplitude-frequency curve of the output impedance and the amplitude-frequency curve of the power grid impedance.
8. The method for correcting the output impedance based on the voltage feedforward channel under the weak current network according to claim 1, wherein the expression of the optimized voltage feedforward transfer function is:
wherein k is 1 、k 2 K 3 The expressions of (2) are respectively:
wherein G is f (s) is a voltage feedforward transfer function, G' f (s) is a tuned voltage feedforward transfer function, alpha is a constant between 0 and 1, s=jω, j 2 = -1, ω is angular frequency, T s In order to sample the period of time,is the phase.
9. The method for correcting the output impedance based on the voltage feedforward channel under the weak current network according to claim 1, wherein the inverter is any one of a photovoltaic inverter, a wind power converter and an energy storage converter.
10. A correction system for output impedance based on a voltage feed-forward path in a weak current network, comprising:
the first determining module is used for determining the cross frequency according to the amplitude-frequency curve of the output impedance of the inverter and the amplitude-frequency curve of the power grid impedance of the grid-connected inverter system; the grid-connected inverter system comprises an inverter end and a power grid end;
the second determining module is used for determining the phase of the output impedance to be lifted according to the phase margin of the grid-connected inverter system at present;
the correction module is used for generating a regulated voltage feedforward transfer function according to the crossover frequency, the phase and the voltage feedforward transfer function of the grid-connected inverter system, and generating corrected output impedance according to the regulated voltage feedforward transfer function so as to realize correction of the output impedance.
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| CN108879781A (en) * | 2018-08-01 | 2018-11-23 | 重庆大学 | A kind of grid-connected current control method based on virtual impedance correction method |
| CN110148943A (en) * | 2019-06-18 | 2019-08-20 | 福州大学 | A kind of LCL gird-connected inverter impedance remodeling procedure for inhibiting power grid background harmonics to influence |
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| CN108879782A (en) * | 2018-08-01 | 2018-11-23 | 国网重庆市电力公司电力科学研究院 | Gird-connected inverter optimal control method based on double-smoothing voltage feed-forward control |
| CN108879781A (en) * | 2018-08-01 | 2018-11-23 | 重庆大学 | A kind of grid-connected current control method based on virtual impedance correction method |
| CN110148943A (en) * | 2019-06-18 | 2019-08-20 | 福州大学 | A kind of LCL gird-connected inverter impedance remodeling procedure for inhibiting power grid background harmonics to influence |
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