CN116316791B - Asymmetric power grid negative sequence voltage phase compensation method based on double d-q phase-locked loops - Google Patents

Asymmetric power grid negative sequence voltage phase compensation method based on double d-q phase-locked loops Download PDF

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CN116316791B
CN116316791B CN202211103310.7A CN202211103310A CN116316791B CN 116316791 B CN116316791 B CN 116316791B CN 202211103310 A CN202211103310 A CN 202211103310A CN 116316791 B CN116316791 B CN 116316791B
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sequence voltage
negative sequence
phase
axis
component
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CN116316791A (en
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吴明灿
高文超
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Sineng Electric 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
    • H02J3/38—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
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • 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
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • 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
    • 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
    • Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks

Abstract

The invention is suitable for the technical field of inverter control, and provides an asymmetric power grid negative sequence voltage phase compensation method and an inverter based on a double d-q phase-locked loop, wherein the method comprises the following steps: converting the three-phase power grid voltage to obtain d-q axis components in a d-q axis two-phase rotation coordinate system; decoupling according to the d-q axis component to obtain a decoupled d-q axis component, wherein the decoupled d-q axis component comprises a decoupled positive sequence voltage component and a decoupled negative sequence voltage component; according to the decoupled negative sequence voltage component on the d-q axis, calculating the sine and cosine values of the phase difference between the decoupled negative sequence voltage component on the d axis and the actual negative sequence voltage vector of the double d-q phase-locked loop; and calculating the compensation phase of the actual negative sequence voltage vector according to the sine and cosine values of the phase difference and the sine and cosine values of the negative sequence voltage phase. The method and the device can compensate the negative sequence voltage phase under the asymmetric power grid, and improve the reactive power compensation capability of the photovoltaic grid-connected inverter in low-voltage ride-through under the asymmetric power grid.

Description

Asymmetric power grid negative sequence voltage phase compensation method based on double d-q phase-locked loops
Technical Field
The invention belongs to the technical field of inverter control, and particularly relates to an asymmetric power grid negative sequence voltage phase compensation method based on a double d-q phase-locked loop.
Background
The photovoltaic grid-connected inverter can stably grid and transmit power on the premise that the inverter can rapidly and accurately detect relevant information such as fundamental frequency, initial phase, positive and negative sequence components and the like of three-phase grid voltage, so that the inverter system effectively avoids the problems of over-current on the inversion side, bus voltage fluctuation and the like caused by sudden change of the three-phase voltage. The double d-q phase-locked loop is a software phase-locked technology, can realize accurate phase locking under a three-phase symmetric power grid, can effectively decouple positive and negative sequence voltages under an asymmetric power grid, and tracks the frequency and the phase of the power grid.
In the current photovoltaic grid-connected power generation system, the grid-connected standard of various countries requires an inverter to have a low-voltage ride through function, and the low-voltage ride through function requires the system to rapidly respond to the change of the power grid voltage and perform reactive current compensation according to the change quantity of the power grid voltage. The premise of realizing the function is that the inverter can accurately and rapidly detect the frequency and phase information of the required grid voltage. With the development of a photovoltaic grid-connected power generation system, the requirements of various countries on the photovoltaic system are higher and higher, and the low voltage ride through under an asymmetric power grid needs to respectively send out positive and negative sequence reactive current according to the change of positive and negative sequence voltage to compensate the change of positive and negative sequence voltage.
When the double d-q phase-locked loop performs positive and negative sequence voltage component phase locking, the default positive and negative sequence voltage components have the same initial phase, and rotate at the same speed in opposite directions in a vector space. In practice, in an asymmetric fault of a power grid, initial phases of positive and negative sequence voltage components are not necessarily the same, so that the negative sequence voltage phase obtained by a double d-q phase-locked loop is inaccurate, the reactive power compensation capability of low-voltage ride through of a photovoltaic grid-connected inverter is low, and the compensation quantity of negative sequence reactive current cannot meet grid-connected requirements.
Disclosure of Invention
The embodiment of the invention provides an asymmetric power grid negative sequence voltage phase compensation method based on a double d-q phase-locked loop, which aims to solve the problems that in the prior art, in the power grid asymmetric fault, when the initial phases of positive and negative sequence voltage components are different, the obtained negative sequence voltage phase of the double d-q phase-locked loop is inaccurate, and the reactive compensation capability of the low-voltage ride through of a photovoltaic grid-connected inverter is low.
The embodiment of the invention is realized by providing an asymmetric power grid negative sequence voltage phase compensation method based on a double d-q phase-locked loop, which comprises the following steps:
converting according to the sampled three-phase grid voltage to obtain a d-q axis component in a d-q axis two-phase rotation coordinate system, wherein the d-q axis component comprises a positive sequence voltage component and a negative sequence voltage component;
under the condition of unbalanced power grid voltage, decoupling is carried out according to the d-q axis component, so as to obtain a decoupled d-q axis component, wherein the decoupled d-q axis component comprises a decoupled positive sequence voltage component and a decoupled negative sequence voltage component;
calculating a sine and cosine value of a phase difference between the decoupled negative sequence voltage component and an actual negative sequence voltage vector of the double d-q phase-locked loop on the d axis according to the decoupled negative sequence voltage component on the d-q axis;
and calculating the compensation phase of the actual negative sequence voltage vector according to the sine and cosine values of the phase difference and the sine and cosine values of the negative sequence voltage phase.
Further, the converting according to the sampled three-phase grid voltage to obtain a d-q axis component in a d-q axis two-phase rotation coordinate system includes:
clark transformation is carried out based on the three-phase power grid voltage, a three-phase static coordinate system is converted into a two-phase alpha-beta static coordinate system, and voltage components on an alpha axis and a beta axis are respectively obtained;
and performing Park conversion on angles of positive sequence voltage and negative sequence voltage based on the voltage components of the alpha axis and the beta axis to obtain the positive sequence voltage component and the negative sequence voltage component on the d-q axis two-phase rotation coordinate system.
Further, performing Park conversion on angles of positive sequence voltage and negative sequence voltage based on the voltage components of the alpha axis and the beta axis to obtain the positive sequence voltage component and the negative sequence voltage component on the d-q axis two-phase rotation coordinate system, including:
calculating the positive sequence voltage component in the d-q axis two-phase rotation coordinate system according to the voltage components of the alpha axis and the beta axis and the sine and cosine values of the angles of the positive sequence voltage and the negative sequence voltage, wherein the positive sequence voltage component comprises a positive sequence voltage component on the d axis and a positive sequence voltage component on the q axis;
and calculating the negative sequence voltage component in the d-q axis two-phase rotation coordinate system according to the voltage components of the alpha axis and the beta axis and the sine and cosine values of the angles of the positive sequence voltage and the negative sequence voltage, wherein the negative sequence voltage component comprises a negative sequence voltage component on the d axis and a negative sequence voltage component on the q axis.
Further, the decoupling according to the d-q axis component, to obtain a d-q axis component after decoupling, includes:
and performing decoupling calculation based on the angles of the positive sequence voltage and the negative sequence voltage, the positive sequence voltage component and the negative sequence voltage component in the d-q axis two-phase rotation coordinate system, and the filtering adjustment component of the d-q axis component to obtain the decoupled positive sequence voltage component and the decoupled negative sequence voltage component.
Further, the decoupling calculation based on the angles of the positive sequence voltage and the negative sequence voltage, the positive sequence voltage component and the negative sequence voltage component in the d-q axis two-phase rotation coordinate system, and the filtering adjustment component of the d-q axis component includes:
respectively calculating positive sequence filtering adjustment components of the d-q axis components and negative sequence filtering adjustment components of the d-q axis components;
according to the positive sequence voltage component, the positive sequence filtering adjusting component of the d-q axis component and the sine and cosine double angle value of the angle of the positive sequence voltage, decoupling and calculating the decoupled positive sequence voltage component of the positive sequence voltage component in the d-q axis two-phase rotation coordinate system;
and according to the negative sequence voltage component, the negative sequence filtering adjusting component of the d-q axis component and the sine and cosine double angle value of the angle of the negative sequence voltage, decoupling and calculating the decoupled negative sequence voltage component of the negative sequence voltage component in the d-q axis two-phase rotation coordinate system.
Further, the calculating a sine and cosine value of a phase difference between the decoupled negative sequence voltage component and an actual negative sequence voltage vector of the dual d-q phase-locked loop on the d-axis according to the decoupled negative sequence voltage component on the d-q axis includes:
calculating the actual negative sequence voltage vector according to the decoupled negative sequence voltage component of the d axis and the decoupled negative sequence voltage component of the q axis in the d-q axis two-phase rotation coordinate system;
calculating a cosine value of a phase difference between the decoupled negative sequence voltage component and the actual negative sequence voltage vector on the d-axis based on the actual voltage vector and the decoupled negative sequence voltage component of the d-axis in the d-q axis two-phase rotation coordinate system;
and calculating a sine value of a phase difference between the decoupled negative sequence voltage component and the actual negative sequence voltage vector on the d-axis based on the actual voltage vector and the decoupled negative sequence voltage component on the q-axis in the d-q axis two-phase rotation coordinate system.
Further, the calculating the compensation phase of the actual negative sequence voltage vector according to the sine and cosine values of the phase difference and the sine and cosine values of the negative sequence voltage phase includes:
calculating the cosine values of the phase difference and the negative sequence voltage phase according to the sine value of the phase difference of the decoupled negative sequence voltage component and the actual negative sequence voltage vector and the sine and cosine values of the negative sequence voltage phase, so as to obtain the cosine value of the actual negative sequence voltage vector;
calculating the sine values of the phase difference and the negative sequence voltage phase according to the sine values of the phase difference of the decoupled negative sequence voltage component and the actual negative sequence voltage vector and the sine and cosine values of the negative sequence voltage phase, and obtaining the sine values of the actual negative sequence voltage vector;
and calculating the compensation phase of the actual negative sequence voltage vector according to the cosine value of the actual negative sequence voltage vector or the sine value of the actual negative sequence voltage vector.
Still further, the calculating the compensation phase of the actual negative sequence voltage vector according to the cosine value of the negative sequence voltage vector or the sine value of the negative sequence voltage vector includes:
calculating an inverse cosine value of the actual negative sequence voltage vector to obtain a compensation phase of the actual negative sequence voltage vector; or (b)
And calculating the arcsine value of the sine value of the actual negative sequence voltage vector to obtain the compensation phase of the actual negative sequence voltage vector.
Still further, after the step of decoupling from the d-q axis component under the grid voltage imbalance condition, the method further includes:
and performing PI regulation and integral transformation on the positive sequence voltage component after q-axis decoupling to obtain the positive sequence voltage phase, and obtaining the negative sequence voltage phase according to the positive sequence voltage phase.
The embodiment of the invention also provides an inverter, which adopts the asymmetric power grid negative sequence voltage phase compensation method based on the double d-q phase-locked loop in the embodiment to carry out negative sequence voltage phase compensation under the asymmetric power grid.
The invention has the beneficial effects that the asymmetric power grid negative sequence voltage phase compensation method based on the double d-q phase-locked loop is provided, the d-q axis component in the d-q axis two-phase rotation coordinate system is obtained by converting according to the sampled three-phase power grid voltage, under the unbalanced power grid voltage condition, the d-q axis component after decoupling is obtained according to the d-q axis component, the d-q axis component after decoupling comprises the positive sequence voltage component after decoupling and the negative sequence voltage component after decoupling, and then the sine and cosine values of the phase difference between the negative sequence voltage component after decoupling and the actual negative sequence voltage vector on the d axis of the double d-q phase-locked loop are calculated according to the negative sequence voltage component after decoupling on the d-q axis; and calculating the compensation phase of the actual negative sequence voltage vector according to the sine and cosine values of the phase difference and the sine and cosine values of the negative sequence voltage phase. Therefore, when the power grid has unbalance faults, the negative sequence voltage phase is compensated by calculating the compensation phase according to the situation that the initial phase difference of the positive sequence voltage and the negative sequence voltage of the double d-q phase-locked loop is different, the problem that the negative sequence voltage phase of the double d-q phase-locked loop is inaccurate under the asymmetric power grid can be effectively solved, and the reactive compensation capability of the photovoltaic grid-connected inverter for low voltage ride-through under the asymmetric power grid is improved.
Drawings
FIG. 1a is a flow chart of an asymmetric power grid negative sequence voltage phase compensation method based on a double d-q phase-locked loop according to an embodiment of the present invention;
FIG. 1b is a positive and negative sequence voltage rotation vector diagram provided by an embodiment of the present invention;
FIG. 2 is a flowchart of step S1 in FIG. 1a according to an embodiment of the present invention;
FIG. 3 is a block diagram of overall control of a dual d-q PLL provided by an embodiment of the present invention;
FIG. 4 is a flowchart of step S2 in FIG. 1a according to an embodiment of the present invention;
FIG. 5 is a flowchart of step S3 in FIG. 1a according to an embodiment of the present invention;
fig. 6 is a flowchart of step S4 in fig. 1a according to the present embodiment of the invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
In the prior art, in the asymmetric fault of the power grid, the initial phases of the positive and negative sequence voltage components are not necessarily the same, so that the phase of the negative sequence voltage obtained by the double d-q phase-locked loop is inaccurate. According to the method, the sine and cosine values of the phase difference between the decoupled negative sequence voltage component and the actual negative sequence voltage vector of the double d-q phase-locked loop on the d-axis are calculated according to the decoupled negative sequence voltage component on the d-q axis, and the compensation phase of the actual negative sequence voltage vector is calculated according to the sine and cosine values of the phase difference and the sine and cosine values of the negative sequence voltage phase. When the power grid has unbalance faults, the negative sequence voltage phase is compensated by calculating the compensation phase, so that the problem that the negative sequence voltage phase of the double d-q phase-locked loop is inaccurate under the asymmetric power grid can be effectively solved, and the reactive compensation capability of the photovoltaic grid-connected inverter for low voltage ride-through under the asymmetric power grid is improved.
Example 1
Referring to fig. 1a, fig. 1a is a flowchart of an asymmetric power grid negative sequence voltage phase compensation method based on a dual d-q phase-locked loop according to the present embodiment. The asymmetric power grid negative sequence voltage phase compensation method based on the double d-q phase-locked loops comprises the following steps:
s1, converting according to the sampled three-phase grid voltage to obtain a d-q axis component in a d-q axis two-phase rotation coordinate system, wherein the d-q axis component comprises a positive sequence voltage component and a negative sequence voltage component.
In this embodiment, the current three-phase grid voltage is collected in real time, and the phase lock of the double d-q phase-locked loop is performed, and the three-phase grid voltage is first converted to obtain a d-q axis component in a d-q axis two-phase rotation coordinate system, where the d-q axis component includes a positive sequence voltage component and a negative sequence voltage component. The conversion comprises Clark conversion and Park conversion in sequence, and positive sequence voltage components and negative sequence voltage components are obtained after Park conversion.
S2, under the condition of unbalanced power grid voltage, decoupling is carried out according to the d-q axis component, and a decoupled d-q axis component is obtained and comprises a decoupled positive sequence voltage component and a decoupled negative sequence voltage component.
When the power grid has unbalance fault, the value obtained through Clark conversion is the sum of components of positive sequence voltage and negative sequence voltage on a two-phase alpha-beta static coordinate system, so that the positive sequence voltage component and the negative sequence voltage component obtained after Park conversion are coupled, and the positive sequence voltage component and the negative sequence voltage component can be decoupled respectively to obtain the positive sequence voltage component after decoupling and the negative sequence voltage component after decoupling.
S3, calculating the sine and cosine values of the phase difference between the decoupled negative sequence voltage component and the actual negative sequence voltage vector of the double d-q phase-locked loop on the d axis according to the decoupled negative sequence voltage component on the d-q axis.
Fig. 1b is a positive-negative sequence voltage rotation vector diagram provided in this embodiment, with reference to fig. 1 b. When the power grid voltage is unbalanced, a positive sequence voltage vector U appears in the d-q axis two-phase rotation coordinate system s + And negative sequence voltage vector U s - Counter-rotating at the same angular velocity. After the phase locking of the double d-q phase-locked loop is successful, in a d-q axis two-phase rotation coordinate system, the positive sequence voltage component U after decoupling is established pdref And positive sequence voltage vector U s + And (5) overlapping. At this time, the positive sequence voltage phase is θ, and the negative sequence voltage phasePhase is-theta, negative sequence voltage vector U s - Is not the correct phase, the decoupled negative sequence voltage component U ndref And the actual negative sequence voltage vector U s - Phase difference betweenCan be based on the negative sequence voltage vector U s - Projection calculations on a negative-sequence coordinate system, i.e. from the decoupled negative-sequence voltage components U on the d-axis and the q-axis ndref And U nqref And (5) calculating to obtain the product.
S4, calculating the compensation phase of the actual negative sequence voltage vector according to the sine and cosine values of the phase difference and the sine and cosine values of the negative sequence voltage phase.
Wherein the negative sequence voltage vector U s - Is of the compensation phase ofBy using sine and cosine theorem, according to sine and cosine values of the negative sequence voltage phase and the decoupled negative sequence voltage component U ndref And the actual negative sequence voltage vector U s - Phase difference between->Calculating the sine and cosine values of (2), and solving the negative sequence voltage vector U s - Compensating phase +.>According to the sine and cosine values of the negative sequence voltage vector U s - Compensating phase +.>The sine and cosine values of (a) calculate a negative sequence voltage vector U s - Compensating phase +.>Finally according to the compensation phase->Negative sequence voltage vector U when phase-locking double d-q phase-locked loop s - And performing phase compensation.
In the embodiment of the invention, as the d-q axis component in the d-q axis two-phase rotation coordinate system is obtained by converting the three-phase power grid voltage obtained by sampling, under the unbalanced condition of the power grid voltage, the d-q axis component after decoupling is obtained according to the d-q axis component, the d-q axis component after decoupling comprises a positive sequence voltage component after decoupling and a negative sequence voltage component after decoupling, and then the sine and cosine values of the phase difference between the negative sequence voltage component after decoupling and the actual negative sequence voltage vector of the double d-q phase-locked loop on the d axis are calculated according to the negative sequence voltage component after decoupling on the d-q axis; and calculating the compensation phase of the actual negative sequence voltage vector according to the sine and cosine values of the phase difference and the sine and cosine values of the negative sequence voltage phase. Therefore, when the power grid has unbalance faults, the negative sequence voltage phase is compensated by calculating the compensation phase according to the situation that the initial phase difference of the positive sequence voltage and the negative sequence voltage of the double d-q phase-locked loop is different, the problem that the negative sequence voltage phase of the double d-q phase-locked loop is inaccurate under the asymmetric power grid can be effectively solved, and the reactive compensation capability of the photovoltaic grid-connected inverter for low voltage ride-through under the asymmetric power grid is improved. In addition, the phase of the negative sequence voltage is compensated, so that the problem of waste of control system resources caused by phase locking of the negative sequence voltage by repeatedly using the phase-locked loop is avoided. And when the power grid fails, the phase locking speed of the negative sequence voltage is faster than that of the phase locking loop which is used for locking the phase of the negative sequence voltage repeatedly.
Example two
On the basis of the first embodiment, as shown in fig. 2, fig. 2 is a flowchart of step S1 in fig. 1a provided in this embodiment. Specifically, step S1 includes:
s21, clark transformation is carried out based on three-phase grid voltage, a three-phase static coordinate system is converted into a two-phase alpha-beta static coordinate system, and voltage components on an alpha axis and a beta axis are respectively obtained.
S22, performing Park conversion on angles of positive sequence voltage and negative sequence voltage based on voltage components of the alpha axis and the beta axis to obtain positive sequence voltage components and negative sequence voltage components on a d-q axis two-phase rotation coordinate system.
In particular, the Clark transformation can transform a three-phase stationary A-B-C coordinate system to a two-phase α - β stationary coordinate system. After the three-phase power grid voltage U is obtained a 、U b And U c Then, the voltage components U in the alpha axis and the beta axis in the two-phase alpha-beta static coordinate system can be obtained through Clark transformation α And U β . The Clark transformation formula is as follows:
in U a 、U b And U c U is the voltage value of the three-phase power grid α And U β Is the voltage component on the alpha and beta axes on a two-phase alpha-beta stationary coordinate system.
More specifically, after the voltage components of the two phases alpha-beta on the alpha axis and the beta axis are calculated, park transformation can be performed based on the angle theta of the positive sequence voltage and the angle-theta of the negative sequence voltage to obtain a positive sequence voltage component U on the two phases d-q axis rotating coordinate system pd And U pq And obtain a negative sequence voltage component U nd And U nq 。
Optionally, the step S22 specifically includes:
and calculating positive sequence voltage components in the d-q axis two-phase rotation coordinate system according to the voltage components of the alpha axis and the beta axis and the sine and cosine values of the angles of the positive sequence voltage and the negative sequence voltage, wherein the positive sequence voltage components comprise positive sequence voltage components on the d axis and positive sequence voltage components on the q axis.
Specifically, the Park transform formula is as follows:
in U pd 、U pq For positive sequence voltage component on d-q axis two-phase rotation coordinate system, U nd 、U nq Seat for d-q axis two-phase rotationNegative sequence voltage components on the label system.
It can be seen that the voltage component U is based on the alpha and beta axes α And U β And the angle theta of the positive sequence voltage, the positive sequence voltage component U on the d axis in the d-q axis two-phase rotation coordinate system can be calculated pd And positive sequence voltage component U on q-axis pq 。
And calculating the negative sequence voltage component in the d-q axis two-phase rotation coordinate system according to the voltage components of the alpha axis and the beta axis and the sine and cosine values of the angles of the positive sequence voltage and the negative sequence voltage, wherein the negative sequence voltage component comprises the negative sequence voltage component on the d axis and the negative sequence voltage component on the q axis.
Also, as shown in connection with equation (2), the voltage components U according to the alpha and beta axes α And U β The sine and cosine values of the angle-theta between the negative sequence voltage and the negative sequence voltage can calculate the negative sequence voltage component U on the d axis in the d-q axis two-phase rotation coordinate system nd And a negative sequence voltage component U on the q-axis nq 。
In this embodiment, clark transformation and Park transformation are sequentially performed on the sampled three-phase grid voltage to obtain a positive sequence voltage component U on the d-axis in a d-q axis two-phase rotation coordinate system pd And positive sequence voltage component U on q-axis pq And a negative sequence voltage component U on the d-axis nd Negative sequence voltage component U on q-axis nq Under the condition of unbalanced power grid voltage, decoupling is carried out according to the d-q axis component to obtain a positive sequence voltage component after decoupling and a negative sequence voltage component after decoupling, then the sine and cosine value of the phase difference between the negative sequence voltage component after decoupling and the actual negative sequence voltage vector of the double d-q phase-locked loop on the d axis is calculated according to the negative sequence voltage component after decoupling on the d-q axis, and the compensation phase of the actual negative sequence voltage vector is calculated according to the sine and cosine value of the phase difference and the sine and cosine value of the negative sequence voltage phase. Therefore, the method and the device can effectively solve the problem that the phase of the negative sequence voltage of the double d-q phase-locked loop is inaccurate under an asymmetric power grid by compensating the phase of the negative sequence voltage through calculating the compensation phase under the condition that the initial phase difference of the positive sequence voltage and the initial phase difference of the negative sequence voltage of the double d-q phase-locked loop are different, and improve the reactive compensation capability of the photovoltaic grid-connected inverter for low voltage ride through under the asymmetric power grid.
Example III
On the basis of the second embodiment, step S2 provided in this embodiment includes: and performing decoupling calculation based on the angles of the positive sequence voltage and the negative sequence voltage, the positive sequence voltage component and the negative sequence voltage component in the d-q axis two-phase rotation coordinate system and the filtering adjustment component of the d-q axis component to obtain a decoupled positive sequence voltage component and a decoupled negative sequence voltage component.
Fig. 3 is an overall control block diagram of the dual d-q phase-locked loop according to the present embodiment, which is shown in fig. 3. As can be seen from fig. 3, the three-phase network voltage U a 、U b And U c The voltage components U in the alpha axis and the beta axis in the two-phase alpha-beta static coordinate system can be obtained through Clark transformation α (U alpha ) And U β (U beta ) Then the voltage component U α And U β Respectively inputting into double d-q phase-locked loops to carry out Park conversion to obtain positive sequence voltage component U on d-q axis two-phase rotation coordinate system pd And U pq And obtain a negative sequence voltage component U nd And U nq . Positive sequence voltage component U pd And U pq Negative sequence voltage component U nd And U nq The logical decoupling operation is carried out according to the filtered adjusting component of the d-q axis component and the angles of the positive sequence voltage and the negative sequence voltage, so as to obtain a positive sequence voltage component U after decoupling pdref And U pqref And a decoupled negative sequence voltage component U ndref And U nqref . Wherein the filtered adjusted component of the d-q axis component is processed by a Low Pass Filter (LPF).
Optionally, referring to fig. 4, fig. 4 is a flowchart of step S2 in fig. 1a provided in this embodiment. The method specifically comprises the following steps:
s41, respectively calculating positive sequence filtering adjustment components of the d-q axis components and negative sequence filtering adjustment components of the d-q axis components.
In the decoupling process, the influence of the high-frequency signal on the phase lock can be avoided by adding a low-pass filter, and the transfer function of the low-pass filter is as follows:
where RC is the time constant of the filter.
Specifically, the positive sequence filtering adjustment component U of the filtered d-q axis component can be calculated by a low-pass filter psd And U psq And a negative sequence filter adjustment component U of the d-q axis component nsd And U nsq . Wherein the positive sequence filter adjusts the component U psd And U psq Namely the positive sequence voltage component U after decoupling pdref And U pqref The amount of the low-pass filter is filtered, and the negative sequence filter adjusts the component U nsd And U nsq Is a negative sequence voltage component U ndref And U nqref The amount after the low pass filter is performed.
S42, according to the positive sequence voltage component, the positive sequence filtering adjustment component of the d-q axis component and the positive cosine double angle value of the angle of the positive sequence voltage, decoupling to calculate the decoupled positive sequence voltage component of the positive sequence voltage component in the d-q axis two-phase rotation coordinate system.
S43, according to the negative sequence voltage component, the negative sequence filtering adjustment component of the d-q axis component and the sine and cosine double angle value of the angle of the negative sequence voltage, decoupling and calculating the decoupled negative sequence voltage component of the negative sequence voltage component in the d-q axis two-phase rotation coordinate system.
The calculation formula for calculating the decoupled positive sequence voltage component and the decoupled negative sequence voltage component is as follows:
in U pdref 、U pqref To be a positive sequence voltage component after decoupling on a two-phase d-q axis two-phase rotation coordinate system, U ndref 、U nqref Is a decoupled negative sequence voltage component; u (U) psd 、U psq 、U nsd 、U nsq Respectively in turn U pdref 、U pqref 、U ndref 、U nqref The amount after the low pass filter is performed.
Specifically, as shown in the formula (4), the voltage component U is based on the positive sequence pd And U pq Positive sequence filtering of d-q axis component adjusts component U psd And U psq The positive-cosine double angle value of the angle of the positive sequence voltage can be decoupled and calculated to obtain a decoupled positive sequence voltage component U of the positive sequence voltage component in a d-q axis two-phase rotation coordinate system pdref And U pqref Amount of the components. Also, according to the negative sequence voltage component U nd And U nq Negative sequence filtering of d-q axis component adjusts component U nsd And U nsq The positive and cosine double angle values of the angle of the negative sequence voltage can be decoupled and calculated to obtain a decoupled negative sequence voltage component U of the negative sequence voltage component in a d-q axis two-phase rotation coordinate system ndref And U nqref 。
Optionally, after step S2, the method further includes:
and performing PI regulation and integral transformation on the positive sequence voltage component after q-axis decoupling to obtain a positive sequence voltage phase, and obtaining a negative sequence voltage phase according to the positive sequence voltage phase.
Referring to FIG. 3, a decoupled U pqref The phase θ of the positive sequence voltage can be obtained by superposition integral transformation and the phase θ of the negative sequence voltage can be obtained according to the phase θ of the positive sequence voltage.
In this embodiment, for U after unbalance fault of power grid pd 、U pq 、U nd 、U nq Decoupling calculation is carried out on the coupling phenomenon to obtain a positive sequence voltage component U after decoupling on a two-phase d-q axis two-phase rotation coordinate system pdref 、U pqref And a decoupled negative sequence voltage component U ndref 、U nqref And according to the positive sequence voltage component U pqref And calculating the phase theta and the phase theta of the positive sequence voltage and the negative sequence voltage to form a closed-loop control successful phase lock. Then according to the negative sequence voltage component U after the decoupling on the d-q axis ndref 、U nqref Calculating the decoupled negative sequence voltage component U of the double d-q phase-locked loop on the d axis ndref And the actual negative sequence voltage vector U s - Sine and cosine values of the phase difference between them according to the phase differenceThe sine and cosine values of the positive sequence voltage phase and the sine and cosine values of the negative sequence voltage phase are calculated, the compensation phase of the actual negative sequence voltage vector is calculated, and the negative sequence voltage phase is compensated according to the compensation phase, so that the problem that the negative sequence voltage phase of the double d-q phase-locked loop is inaccurate under an asymmetric power grid can be effectively solved, and the reactive compensation capability of the photovoltaic grid-connected inverter for low voltage ride through under the asymmetric power grid is improved.
Example IV
Based on the third embodiment, as shown in fig. 5, fig. 5 is a flowchart of step S3 in fig. 1a provided in this embodiment. Specifically, step S3 includes:
s51, calculating an actual negative sequence voltage vector according to the negative sequence voltage component after d-axis decoupling and the negative sequence voltage component after q-axis decoupling in the d-q-axis two-phase rotation coordinate system.
S52, calculating the cosine value of the phase difference between the negative sequence voltage component after decoupling and the actual negative sequence voltage vector on the d axis based on the actual voltage vector and the negative sequence voltage component after decoupling in the d-axis two-phase rotation coordinate system.
S53, calculating a sine value of a phase difference between the negative sequence voltage component after decoupling and the actual negative sequence voltage vector on the d axis based on the actual voltage vector and the negative sequence voltage component after decoupling in the d-q axis two-phase rotation coordinate system.
Specifically, the actual negative sequence voltage vector U is calculated s - The calculation formulas of the cosine value and the sine value of the phase difference between the negative sequence voltage component and the actual negative sequence voltage vector after the decoupling on the d axis are as follows:
from the above equation (5), it can be seen that according to the decoupled negative sequence voltage component U ndref 、U nqref The square sum root number of (1) can be calculated to obtain the actual negative sequence voltage vector U s - Based on a negative sequence voltage component U ndref And the actual negative sequence voltage vector U s - Can calculate and obtain the negative sequence voltage component and the actual negative sequence voltage vector after decoupling on the d axisCosine value of the phase difference of the quantityBased on a negative sequence voltage component U nqref And the actual negative sequence voltage vector U s - The sine value of the phase difference between the negative sequence voltage component and the actual negative sequence voltage vector after the decoupling on the d axis can be calculated>
In this embodiment, when the grid voltage is unbalanced, the phase of the negative sequence voltage vector in the d-q rotating coordinate system of the negative sequence voltage is set up, so that the compensation phase of the actual negative sequence voltage vector is calculated by calculating the sine and cosine values of the phase difference between the decoupled negative sequence voltage component of the double d-q phase-locked loop on the d axis and the actual negative sequence voltage vector and combining the sine and cosine values of the negative sequence voltage phase, and the negative sequence voltage phase is compensated according to the compensation phase, so that the problem that the negative sequence voltage phase of the double d-q phase-locked loop under the asymmetric grid is inaccurate can be effectively solved, and the reactive compensation capability of the photovoltaic grid-connected inverter under the asymmetric grid for low voltage ride through is improved.
Example five
Based on the fourth embodiment, as shown in fig. 6, fig. 6 is a flowchart of step S4 in fig. 1a provided in this embodiment. Specifically, step S4 includes:
s61, calculating the cosine values of the phase difference and the negative sequence voltage phase according to the sine value of the phase difference of the decoupled negative sequence voltage component and the actual negative sequence voltage vector and the sine and cosine value of the negative sequence voltage phase, and obtaining the cosine value of the actual negative sequence voltage vector.
S62, calculating the sine values of the phase difference and the negative sequence voltage phase according to the sine value of the phase difference of the decoupled negative sequence voltage component and the actual negative sequence voltage vector and the sine value and the cosine value of the negative sequence voltage phase, and obtaining the sine value of the actual negative sequence voltage vector.
And S63, calculating the compensation phase of the actual negative sequence voltage vector according to the cosine value of the actual negative sequence voltage vector or the sine value of the actual negative sequence voltage vector.
Specifically, a negative sequence voltage vector U s - Is of the compensation phase ofThe negative sequence voltage vector U can be obtained according to the cosine law s - Compensating phase +.>Sine and cosine values->And->Based on negative sequence voltage vector U s - Is of the compensation phase of (a)Sine and cosine values->And->Can calculate a negative sequence voltage vector U s - Compensating phase +.>The specific calculation formula is as follows:
optionally, the step S53 includes:
calculating an inverse cosine value of the actual negative sequence voltage vector to obtain a compensation phase of the actual negative sequence voltage vector; or (b)
And calculating the arcsine value of the sine value of the actual negative sequence voltage vector to obtain the compensation phase of the actual negative sequence voltage vector.
Calculating a negative sequence voltage vector U by combining the formula (6) s - Is of the compensation phase of (a)The negative sequence voltage vector U can be inverted by an inverse cosine function s - Compensating phase +.>Is->Calculating an inverse cosine value to obtain a negative sequence voltage vector U s - Compensating phase +.>The negative sequence voltage vector U can also be mapped by an arcsine function s -compensation phase->Is->Calculating an arcsine value to obtain a negative sequence voltage vector U s - Compensating phase +.>
In this embodiment, when the grid voltage is unbalanced, the phase of the negative sequence voltage vector in the d-q rotation coordinate system of the established negative sequence voltage has a phase difference, so the sine value of the phase difference between the decoupled negative sequence voltage component and the actual negative sequence voltage vector of the double d-q phase-locked loop on the d axis is calculatedAnd cosine value->Calculating the compensation phase of the actual negative sequence voltage vector by combining the sine and cosine values of the negative sequence voltage phase>According to compensation phase->The negative sequence voltage phase is compensated, so that the problem that the negative sequence voltage phase of the double d-q phase-locked loop is inaccurate under an asymmetric power grid can be effectively solved, and the reactive compensation capability of the photovoltaic grid-connected inverter for low voltage ride through under the asymmetric power grid is improved.
Example six
The embodiment of the invention also provides an inverter, which adopts the asymmetric power grid negative sequence voltage phase compensation method based on the double d-q phase-locked loop in the first to fifth embodiments to carry out negative sequence voltage phase compensation under the asymmetric power grid.
In the embodiment of the present invention, the asymmetric power grid negative sequence voltage phase compensation method based on the double d-q phase-locked loop in each embodiment may be implemented on the inverter provided in this embodiment, that is, on the inverter provided in this embodiment, the negative sequence voltage phase compensation may be performed under the asymmetric power grid by the asymmetric power grid negative sequence voltage phase compensation method based on the double d-q phase-locked loop. The asymmetric power grid negative sequence voltage phase compensation method based on the double d-q phase-locked loop is capable of obtaining d-q axis components in a d-q axis two-phase rotation coordinate system by converting according to three-phase power grid voltages obtained by sampling, decoupling is carried out according to the d-q axis components under the unbalanced condition of power grid voltages to obtain decoupled d-q axis components, the decoupled d-q axis components comprise decoupled positive sequence voltage components and decoupled negative sequence voltage components, and then sine and cosine values of phase differences between the decoupled negative sequence voltage components of the double d-q phase-locked loop on the d axis and actual negative sequence voltage vectors are calculated according to the decoupled negative sequence voltage components on the d-q axis; and calculating the compensation phase of the actual negative sequence voltage vector according to the sine and cosine values of the phase difference and the sine and cosine values of the negative sequence voltage phase. Therefore, when the power grid has unbalance faults, the negative sequence voltage phase is compensated by calculating the compensation phase according to the situation that the initial phase difference of the positive sequence voltage and the negative sequence voltage of the double d-q phase-locked loop is different, the problem that the negative sequence voltage phase of the double d-q phase-locked loop is inaccurate under the asymmetric power grid can be effectively solved, and the reactive compensation capability of the photovoltaic grid-connected inverter for low voltage ride-through under the asymmetric power grid is improved. Therefore, the inverter provided in this embodiment can also achieve the above embodiments and technical effects, and will not be described herein.
The terms first, second and the like in the description and in the claims or in the above-described figures, are used for distinguishing between different objects and not necessarily for describing a sequential or chronological order. Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present application. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Those of skill in the art will explicitly and implicitly appreciate that the embodiments described herein may be combined with other embodiments.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.

Claims (9)

1. The asymmetric power grid negative sequence voltage phase compensation method based on the double d-q phase-locked loops is characterized by comprising the following steps of:
converting according to the sampled three-phase grid voltage to obtain a d-q axis component in a d-q axis two-phase rotation coordinate system, wherein the d-q axis component comprises a positive sequence voltage component and a negative sequence voltage component;
under the condition of unbalanced power grid voltage, decoupling is carried out according to the d-q axis component, so as to obtain a decoupled d-q axis component, wherein the decoupled d-q axis component comprises a decoupled positive sequence voltage component and a decoupled negative sequence voltage component;
calculating a sine and cosine value of a phase difference between the decoupled negative sequence voltage component and an actual negative sequence voltage vector of the double d-q phase-locked loop on the d axis according to the decoupled negative sequence voltage component on the d-q axis;
calculating the cosine values of the phase difference and the negative sequence voltage phase according to the sine value of the phase difference of the decoupled negative sequence voltage component and the actual negative sequence voltage vector and the sine and cosine values of the negative sequence voltage phase, so as to obtain the cosine value of the actual negative sequence voltage vector;
calculating the sine values of the phase difference and the negative sequence voltage phase according to the sine values of the phase difference of the decoupled negative sequence voltage component and the actual negative sequence voltage vector and the sine and cosine values of the negative sequence voltage phase, and obtaining the sine values of the actual negative sequence voltage vector;
calculating a compensation phase of the actual negative sequence voltage vector according to the cosine value of the actual negative sequence voltage vector or the sine value of the actual negative sequence voltage vector;
negative sequence voltage vector U s - Is of the compensation phase ofWherein, - θ represents the angle of the negative sequence voltage, +.>Representing the decoupled negative sequence voltage component and the actual negative sequence voltage vector U s - A phase difference between them;
based on negative sequence voltage vector U s - Is of the compensation phase of (a)Sine and cosine values->And->Calculating a negative sequence voltage vector U s - Compensating phase +.>The following calculation formula is adopted:
2. the method of claim 1, wherein said converting from the sampled three-phase grid voltage to obtain a d-q axis component in a d-q axis two-phase rotating coordinate system comprises:
clark transformation is carried out based on the three-phase power grid voltage, a three-phase static coordinate system is converted into a two-phase alpha-beta static coordinate system, and voltage components on an alpha axis and a beta axis are respectively obtained;
and performing Park conversion on angles of positive sequence voltage and negative sequence voltage based on the voltage components of the alpha axis and the beta axis to obtain the positive sequence voltage component and the negative sequence voltage component on the d-q axis two-phase rotation coordinate system.
3. The method of claim 2, wherein performing Park transformation on angles of positive sequence voltage and negative sequence voltage based on the voltage components of the α -axis and the β -axis to obtain the positive sequence voltage component and the negative sequence voltage component on the d-q axis two-phase rotation coordinate system, comprises:
calculating the positive sequence voltage component in the d-q axis two-phase rotation coordinate system according to the voltage components of the alpha axis and the beta axis and the sine and cosine values of the angles of the positive sequence voltage and the negative sequence voltage, wherein the positive sequence voltage component comprises a positive sequence voltage component on the d axis and a positive sequence voltage component on the q axis;
and calculating the negative sequence voltage component in the d-q axis two-phase rotation coordinate system according to the voltage components of the alpha axis and the beta axis and the sine and cosine values of the angles of the positive sequence voltage and the negative sequence voltage, wherein the negative sequence voltage component comprises a negative sequence voltage component on the d axis and a negative sequence voltage component on the q axis.
4. The method of claim 3, wherein said decoupling from said d-q axis component results in a decoupled d-q axis component comprising:
and performing decoupling calculation based on the angles of the positive sequence voltage and the negative sequence voltage, the positive sequence voltage component and the negative sequence voltage component in the d-q axis two-phase rotation coordinate system, and the filtering adjustment component of the d-q axis component to obtain the decoupled positive sequence voltage component and the decoupled negative sequence voltage component.
5. The method of claim 4, wherein the decoupling calculation based on the angles of the positive and negative sequence voltages, the positive sequence voltage component and the negative sequence voltage component in the d-q axis two-phase rotation coordinate system, and the filtered adjustment component of the d-q axis component comprises:
respectively calculating positive sequence filtering adjustment components of the d-q axis components and negative sequence filtering adjustment components of the d-q axis components;
according to the positive sequence voltage component, the positive sequence filtering adjusting component of the d-q axis component and the sine and cosine double angle value of the angle of the positive sequence voltage, decoupling and calculating the decoupled positive sequence voltage component of the positive sequence voltage component in the d-q axis two-phase rotation coordinate system;
and according to the negative sequence voltage component, the negative sequence filtering adjusting component of the d-q axis component and the sine and cosine double angle value of the angle of the negative sequence voltage, decoupling and calculating the decoupled negative sequence voltage component of the negative sequence voltage component in the d-q axis two-phase rotation coordinate system.
6. The method of claim 1, wherein said calculating a sine and cosine value of a phase difference between said decoupled negative sequence voltage component and an actual negative sequence voltage vector of said dual d-q phase-locked loop on the d-axis from said decoupled negative sequence voltage component on the d-q axis comprises:
calculating the actual negative sequence voltage vector according to the decoupled negative sequence voltage component of the d axis and the decoupled negative sequence voltage component of the q axis in the d-q axis two-phase rotation coordinate system;
calculating a cosine value of a phase difference between the decoupled negative sequence voltage component and the actual negative sequence voltage vector on the d-axis based on the actual negative sequence voltage vector and the decoupled negative sequence voltage component of the d-axis in the d-q axis two-phase rotation coordinate system;
and calculating a sine value of a phase difference between the decoupled negative sequence voltage component and the actual negative sequence voltage vector on the d-axis based on the actual negative sequence voltage vector and the decoupled negative sequence voltage component of the q-axis in the d-q axis two-phase rotation coordinate system.
7. The method of claim 1, wherein the calculating the compensation phase of the actual negative sequence voltage vector from the cosine value of the negative sequence voltage vector or the sine value of the negative sequence voltage vector comprises:
calculating an inverse cosine value of the actual negative sequence voltage vector to obtain a compensation phase of the actual negative sequence voltage vector; or (b)
And calculating the arcsine value of the sine value of the actual negative sequence voltage vector to obtain the compensation phase of the actual negative sequence voltage vector.
8. The method of claim 1, further comprising, after said step of decoupling from said d-q axis component under grid voltage imbalance conditions:
and performing PI regulation and integral transformation on the positive sequence voltage component after q-axis decoupling to obtain a positive sequence voltage phase, and obtaining the negative sequence voltage phase according to the positive sequence voltage phase.
9. An inverter characterized in that negative sequence voltage phase compensation is performed under an asymmetric power network using an asymmetric power network negative sequence voltage phase compensation method comprising a double d-q phase locked loop based on any one of claims 1-8.
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