CN111490541B - Three-phase inverter phase locking technology suitable for extreme power quality condition - Google Patents

Three-phase inverter phase locking technology suitable for extreme power quality condition Download PDF

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CN111490541B
CN111490541B CN202010422028.XA CN202010422028A CN111490541B CN 111490541 B CN111490541 B CN 111490541B CN 202010422028 A CN202010422028 A CN 202010422028A CN 111490541 B CN111490541 B CN 111490541B
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grid voltage
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power
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CN111490541A (en
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朱见涛
曹振武
郭振鹏
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Zhong Tengwei Network Beijing Technology 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
    • 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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

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

Abstract

The invention provides a phase locking method and system for a three-phase inverter under an extreme power quality condition and an evaluation system for power quality analysis. The method comprises a power grid voltage sampling step, a power grid voltage conversion step, a power grid voltage signal filtering step and a power grid voltage positive and negative sequence separation step. A grid voltage sampling step, namely, sampling the voltage of a photovoltaic grid for multiple times by utilizing a plurality of Remote Terminal Units (RTUs) to obtain multiple voltage sampling signals; the power grid voltage transformation step executes the coordinate system transformation operation of the power grid voltage signal; in the power grid voltage filtering step, a harmonic signal for converting a power grid voltage signal is filtered by adopting a generalized second-order integrator; and in the power grid voltage positive and negative sequence separation step, the power grid voltage is subjected to positive and negative sequence separation by using a double synchronous rotating coordinate system method to obtain a three-phase balanced power grid voltage positive sequence component. The method fully considers the actual running condition of the power grid with poor power quality, and can improve the success rate of low voltage ride through of the inverter.

Description

Three-phase inverter phase locking technology suitable for extreme power quality condition
Technical Field
The invention belongs to the technical field of grid-connected control, and particularly relates to a three-phase inverter phase-locking method and system suitable for extreme power quality conditions, an evaluation system for power quality analysis and a computer-readable storage medium for realizing the method.
Background
With the emergence of energy crisis and high oil prices, concern about climate change and increasing government support, the increase in large-scale utilization of renewable energy power generation is being promoted. Photovoltaic power generation is an important renewable energy power generation form. In places with large power grids, photovoltaic power generation can be operated in a grid-connected mode, and an inverter is a core device for new energy power generation grid-connected and has a lot of applications. Not only in the application scenario of photovoltaic power generation, the inverter is also the core device of the energy storage system.
With the increasing demand of people for living of materials and the increasing of energy consumption, clean energy such as solar energy, wind energy and the like gradually become novel renewable energy which can be consumed.
A photoVoltaic power generating system (PV) is a clean and efficient renewable energy power generating system. The photovoltaic effect can be utilized to directly convert solar radiation energy into electric energy. The system is composed of equipment such as a photovoltaic array, a storage battery pack, a storage battery controller, an inverter and the like, and forms a microgrid.
When the microgrid runs in an island mode, because a large power grid is not used as a support for the voltage and the frequency of the microgrid bus, and the inverter has the characteristics of small inertia and poor overload capacity, various power quality problems are easily caused, and the problem of microgrid voltage imbalance caused by unbalanced load is the most prominent one. When the problem of load asymmetry in the low-voltage microgrid is serious, normal operation of electric equipment in the system can be directly influenced, and even the system can be unstable.
One of the effective ways to eliminate the unbalanced voltage is by installing a parallel compensation device, but this obviously adds additional cost. And the inverter in the microgrid is used as a power electronic device and has strong controllability. For inverters such as energy storage inverters and the like used for establishing voltage and frequency of the microgrid in the microgrid, the active power and reactive power output by the inverters can be controlled by using a proper control method, and meanwhile, the inverters can have the equipartition capacity for negative sequence current and the compensation capacity for asymmetric voltage.
The Chinese patent application with the application number of CN201110398433.3 provides a three-phase inverter for a solar photovoltaic grid-connected system, which comprises an inverter circuit, a control circuit, a filter circuit and a detection circuit, wherein the control circuit comprises a DSP (digital signal processor), a protection module and a digital phase locking module for locking the voltage phase of a power grid, the digital phase locking module comprises a digital phase discriminator, a digital filter and a digital controlled oscillator which are sequentially connected, the digital phase discriminator detects the phase difference between an input signal and an output signal by comparing the input signal with the output signal, the digital filter filters the input signal, and the digital controlled oscillator is used for adjusting the phase difference of the digital signal. The scheme can carry out digital phase locking on the voltage of the power grid, can effectively prevent the phenomenon of voltage phase jitter or lock loss, and ensures the normal operation of the solar photovoltaic grid-connected system.
However, synchronization of the inverter with the voltage of a large grid is very important due to the need for grid-tie operation. The power generation mechanism of new energy is different from that of the traditional power system, so the phase locking technology of the new energy is also essentially different. In the new energy power generation system, the phase synchronization with the large power grid is completed by the internal control of the inverter. The phase-locked loop is an important link in the control of the inverter, and the phase-locked loop greatly influences the electric energy quality of the output current of the inverter. And when the power system is in fault to cause islanding or single-phase voltage loss, whether the phase-locked loop can work stably directly determines the low/zero voltage ride through capability of the inverter. The phase locking technology of the inverter commonly used at present needs to be realized by detecting the voltage of a large power grid to be linked, the phase locking achievement can be realized when the voltage and the power quality of the large power grid are normal, but when the power quality has a serious problem, the situation of phase locking failure can occur in a long time. The failure of phase locking can cause the electric energy quality of grid-connected current to be reduced, and the low-voltage ride through can not be completed.
Disclosure of Invention
In order to solve the technical problems, the invention provides a phase locking method and system for a three-phase inverter under an extreme power quality condition and an evaluation system for power quality analysis. The method comprises a power grid voltage sampling step, a power grid voltage conversion step, a power grid voltage signal filtering step and a power grid voltage positive and negative sequence separation step. A grid voltage sampling step, namely, sampling the voltage of a photovoltaic grid for multiple times by utilizing a plurality of Remote Terminal Units (RTUs) to obtain multiple voltage sampling signals; the power grid voltage transformation step executes the coordinate system transformation operation of the power grid voltage signal; in the power grid voltage filtering step, a harmonic signal for converting a power grid voltage signal is filtered by adopting a generalized second-order integrator; and in the power grid voltage positive and negative sequence separation step, the power grid voltage is subjected to positive and negative sequence separation by using a double synchronous rotating coordinate system method to obtain a three-phase balanced power grid voltage positive sequence component. The method fully considers the actual running condition of the power grid with poor power quality, and can improve the success rate of low voltage ride through of the inverter.
Specifically, in a first aspect of the invention, a three-phase inverter phase locking method suitable for extreme power quality conditions is provided, and the method comprises a power grid voltage sampling step, a power grid voltage conversion step, a power grid voltage signal filtering step and a power grid voltage positive and negative sequence separation step;
as a first advantage of the present invention, in the grid voltage sampling step, a plurality of Remote Terminal Units (RTUs) are used to sample the voltage of the photovoltaic grid for a plurality of times, so as to obtain a plurality of voltage sampling signals;
and, each of said Remote Terminal Units (RTU) is connected to one of said edge computing terminals,
acquiring a voltage value U, a frequency f, a waveform signal and a harmonic signal THD of the current photovoltaic power grid based on a plurality of voltage sampling signals acquired by the Remote Terminal Unit (RTU);
and the edge computing terminal collects the steady-state data, the transient-state data and the switching state data of the electric energy quality based on the voltage sampling signal and executes an edge computing process. The edge computing terminal is configured with various load models, including a vehicle charging model, a user electricity utilization model, a photovoltaic model and a wind power model.
And the edge computing terminal is configured with various load models, and the power quality is predicted based on the various load models.
Preferably, the edge computing terminal performs power quality analysis on the voltage sampling signal, and performs a coordinate system transformation operation of the grid voltage signal based on a result of the power quality analysis, and the method specifically includes:
at the time of sampling i, a voltage sampling signal { U }ai，Ubi，UciAccess edge computing device Mi；
By the edge computing device MiCalculating the output load LiObtaining the output load set L ═ { L ═ L of all edge computing devices1，L2，......Ln}；
Judging whether the element values in the output load set L accord with uniform distribution within a preset range or not;
if not, executing coordinate system conversion operation of the power grid voltage signal, wherein the coordinate system conversion operation converts the three-phase power supply voltage value of the photovoltaic power grid into a two-dimensional voltage value under a two-phase static coordinate system;
and if so, returning to the step of sampling the grid voltage.
As another advantage of the present invention, in the grid voltage transforming step, a plurality of edge computing terminals are adopted to receive the plurality of voltage sampling signals, perform power quality analysis on the voltage sampling signals, and perform coordinate system transformation operation on the grid voltage signals based on the result of the power quality analysis to obtain transformed grid voltage signals;
in the power grid voltage filtering step, a generalized second-order integrator is adopted to filter harmonic signals of the converted power grid voltage signals;
the method comprises the following steps of performing positive and negative sequence separation on the power grid voltage by using a double synchronous rotating coordinate system method, removing a negative sequence component of the power grid voltage, and obtaining a three-phase balanced power grid voltage positive sequence component;
the method comprises the following steps that an edge computing terminal performs power quality analysis on the voltage sampling signal, and executes coordinate system transformation operation of the power grid voltage signal based on the result of the power quality analysis, and specifically comprises the following steps:
at the time of sampling i, a voltage sampling signal { U }ai，Ubi，UciAccess edge computing device Mi；
By the edge computing device MiCalculating the output load LiObtaining the output load set L ═ { L ═ L of all edge computing devices1，L2，......Ln}；
Judging whether the element values in the output load set L accord with uniform distribution within a preset range or not;
if not, executing coordinate system conversion operation of the power grid voltage signal, wherein the coordinate system conversion operation converts the three-phase power supply voltage value of the photovoltaic power grid into a two-dimensional voltage value under a two-phase static coordinate system;
and if so, returning to the step of sampling the grid voltage.
In the power grid voltage filtering step, a generalized second-order integrator is adopted to filter harmonic signals of the converted power grid voltage signals;
and in the power grid voltage positive and negative sequence separation step, the power grid voltage is subjected to positive and negative sequence separation by using a double synchronous rotating coordinate system method, the negative sequence component of the power grid voltage is removed, and the three-phase balanced power grid voltage positive sequence component is obtained.
In a second aspect of the present invention, a phase-locked system for a three-phase inverter suitable for use under extreme power quality conditions is provided, where the phase-locked system includes a voltage signal sampling terminal, an edge computing terminal, a transformation subsystem, a filtering subsystem, and a separation subsystem, and is configured to execute the aforementioned phase-locked method for the three-phase inverter, where the voltage signal sampling terminal executes the grid voltage sampling step, and the edge computing terminal executes the edge computing; the transformation subsystem executes the power grid voltage transformation step, the filtering subsystem executes the power grid voltage filtering step, and the separation subsystem executes the power grid voltage positive and negative sequence separation step.
In a third aspect of the present invention, an evaluation system for power quality analysis is provided, the evaluation system is connected to the aforementioned three-phase inverter phase-locking system suitable for extreme power quality conditions, and is used for evaluating and predicting a power instruction of a photovoltaic power grid, so as to implement the three-phase inverter phase-locking method suitable for extreme power quality conditions.
The above method can be implemented in a computer system under comprehensive control, and therefore, the present invention also provides a computer-readable storage medium having stored thereon computer-executable instruction codes, which are executed by a memory and a processor, for implementing the aforementioned three-phase inverter phase-locking method.
In summary, the invention discloses a phase locking method for a three-phase inverter, which can adapt to poor power quality conditions. The phase-locked method of the three-phase inverter is suitable for poor electric energy quality conditions, and aims to solve the problem that the phase-locked failure of the grid-connected inverter is caused by poor electric energy quality of grid voltage. The method introduces a generalized second-order integral link and a double synchronous rotation coordinate conversion link respectively to filter harmonic distortion of the power grid voltage, and carries out positive-negative sequence separation on the power grid voltage to remove the influence of three-phase unbalance on phase locking. The method fully considers the actual running condition of the power grid with poor power quality, can improve the phase-locking success rate of the inverter, and can not cause the phase-locking failure of the inverter under the condition of high harmonic content and high three-phase unbalance degree. Meanwhile, the success rate of low voltage ride through of the inverter can be improved.
Further advantages of the invention will be apparent in the detailed description section in conjunction with the drawings attached hereto.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is an overall architecture diagram of a three-phase inverter phase-locked system suitable for use in extreme power quality conditions in accordance with an embodiment of the present invention;
FIGS. 2-3 are flow charts of a method for implementing a three-phase inverter phase lock for extreme power quality conditions using the system of FIG. 1;
FIG. 4 is a graph of the abc axis versus the α β axis for the arrangement of FIGS. 1-3;
FIG. 5 is a schematic diagram of the generalized second order integrator processing quadrature signals used in the arrangements illustrated in FIGS. 1-3;
FIG. 6 is a schematic diagram of a power quality assessment system used in the arrangements of FIGS. 1 and 2;
FIG. 7 is a preferred embodiment for performing power quality assessment;
FIG. 8 is a schematic illustration of whether the element values of FIG. 7 conform to a uniform distribution within a predetermined range;
fig. 9 is a schematic diagram of an experimental result of the phase lock according to the technical solution of the present invention.
Detailed Description
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts. The invention is further described with reference to the following drawings and detailed description.
As described in the background art, the phase-locking effect of the inverter is often affected by the imbalance of the harmonic and the three phases of the voltage, which results in the phase-locking failure, so that various embodiments of the present invention provide a novel phase-locking technique, and the method of using the generalized second-order integral and the bi-synchronous rotation of the coordinate axes is used to well implement the harmonic filtering of the grid voltage and the removal of the negative-sequence voltage component. The novel phase locking technology can well complete phase locking work under the condition of poor electric energy quality.
Referring to fig. 1, an overall architecture diagram of a three-phase inverter phase-locked system suitable for extreme power quality conditions is shown according to an embodiment of the present invention.
In fig. 1, the phase-locked system includes a voltage signal sampling terminal, an edge calculation terminal, a transformation subsystem, a filtering subsystem, and a separation subsystem.
Preferably, the voltage signal sampling terminal is a remote terminal unit. A Remote Terminal Unit (RTU), a special computer measurement and control Unit with modular structure designed for long communication distance and severe industrial field environment.
Each remote terminal unit is connected with an edge computing terminal and then connected with the transformation subsystem.
The plurality of edge computing terminals are connected to a power quality assessment system.
On the basis of fig. 1, see fig. 2-3.
Fig. 2-3 are flow charts of methods for implementing phase locking for a three-phase inverter suitable for extreme power quality conditions using the system of fig. 1.
The method of fig. 2 includes a grid voltage sampling step, a grid voltage transformation step, a grid voltage signal filtering step, and a grid voltage positive and negative sequence separation step;
specifically, in the grid voltage sampling step, a plurality of Remote Terminal Units (RTUs) are used for sampling the voltage of the photovoltaic grid for a plurality of times to obtain a plurality of voltage sampling signals;
the power grid voltage transformation step is to adopt a plurality of edge computing terminals to receive the voltage sampling signals, perform power quality analysis on the voltage sampling signals, and execute coordinate system transformation operation of the power grid voltage signals based on the result of the power quality analysis to obtain transformed power grid voltage signals;
in the power grid voltage filtering step, a generalized second-order integrator is adopted to filter harmonic signals of the converted power grid voltage signals;
and in the power grid voltage positive and negative sequence separation step, the power grid voltage is subjected to positive and negative sequence separation by using a double synchronous rotating coordinate system method, the negative sequence component of the power grid voltage is removed, and the three-phase balanced power grid voltage positive sequence component is obtained.
In fig. 1, a voltage signal sampling terminal performs the grid voltage sampling step, and an edge calculation terminal performs the edge calculation; the transformation subsystem executes the power grid voltage transformation step, the filtering subsystem executes the power grid voltage filtering step, and the separation subsystem executes the power grid voltage positive and negative sequence separation step.
Fig. 3 summarizes the specific steps of the above method. Firstly, a sampling signal of the power grid voltage is obtained through a voltage sampling hardware circuit, and the sampled signal is A, B, C three-phase power grid voltage signal. And after the three-phase power grid voltage signal is obtained, 3/2 transformation is carried out on the power grid voltage, and the numerical value of the alpha-beta coordinate system of the power grid voltage is obtained. Then, a harmonic signal of the power grid voltage is filtered by utilizing a generalized second-order integrator, and an alpha-beta coordinate coefficient value of the power grid voltage without harmonic distortion can be obtained, but the problem that the three-phase imbalance still exists in the power grid voltage at the moment. And finally, performing positive-negative sequence separation on the power grid voltage by using a double synchronous rotating coordinate system method, removing the negative sequence component of the power grid voltage, and obtaining the three-phase balanced positive sequence component of the power grid voltage. The phase angle of the power grid voltage is calculated more accurately by using the harmonic-free three-phase balanced positive sequence component, and the phase locking link of the inverter is not easy to fail.
More specifically, referring to the coordinate axis relationship described in fig. 4, abc → α β transformation is performed on the collected grid voltage, and the transformation formula is shown as the following formula.
Figure BDA0002497310340000091
The inverter is used for phase locking by collecting line voltage on the filter capacitor, and is influenced by a power grid and an inverter bridge, the three-phase voltage on the capacitor contains a large amount of harmonic waves, and the harmonic waves cause that harmonic waves are also superposed on the converted alpha beta signal, so that the subsequent operation is influenced.
The second-order generalized integrator can well solve the problem of harmonic waves in sinusoidal components. Fig. 5 is a schematic diagram of a second-order generalized integrator processing quadrature signals. The input is a signal under a voltage rectangular coordinate system obtained by converting a power grid voltage signal through abc → alpha beta, K is a constant for adjusting the system bandwidth, and a signal which is completely synchronous with the input signal and has a phase angle of 90 degrees with the input signal can be obtained after the processing of a second-order generalized integrator. Harmonic components of the output signal are rejected.
If three-phase imbalance exists in the phase voltage of the power system, the voltage can be decomposed into a positive sequence, a negative sequence and a zero sequence. The zero sequence voltage is a common mode component, and the zero sequence component of the phase voltage can be counteracted by taking the three-phase line voltage. Therefore, the unbalanced three-phase line voltage needs to be subjected to positive and negative sequence decomposition, and the phase-locked loop only locks the phase for the positive sequence voltage.
Figure BDA0002497310340000101
Figure BDA0002497310340000102
Let vector V+And coordinate axis d+q+Relatively stationary, the projection obtains a DC component denoted D+、Q+(ii) a Similarly, vector V-And coordinate axis d-q-Relatively stationary, the projection obtains a DC component denoted D-、Q-. Will V-To d+Up projection, i.e. D-、Q-At d+On-axis projection D-_d+、Q-_d+And d is+And d-The angle therebetween is 2 ω t. So as to d+Positive in the positive direction of the axis, D-_d+、Q-_d+The expression of (a) is as follows:
Figure BDA0002497310340000103
Figure BDA0002497310340000104
so that the resultant vector V of the voltages is at d+On-axis projection, the expression is as follows:
d+＝D++D-·cos(2ωt)+Q-·sin(2ωt)
according to the derivation process, the resultant voltage vector V at q can be obtained+、d-、q-The projection expression above is as follows:
q+＝Q+-D-·sin(2ωt)+Q-·cos(2ωt)
d-＝D-+D+·cos(2ωt)-Q+·sin(2ωt)
q-＝Q-+D+·sin(2ωt)+Q+·cos(2ωt)
as can be seen from the above four formulas, the projections of the voltage vector V on the four rotation coordinate axes are all made of direct currentA component and a frequency doubled component. The purpose of phase locking the positive sequence component is to ensure Q by feedback adjustment of phase angle-Is zero; and D+Multiplying by a suitable coefficient may represent the magnitude or effective value of the voltage. Therefore, the direct current component of the projection by α β → dq transformation is the next step, so the four equations are transformed to obtain the following expression.
Figure BDA0002497310340000111
By adding a low-pass filter at an appropriate position according to the above formula, the solution D can be drawn+、Q+、D-、Q-. To obtain Q+Then, according to the instantaneous reactive theory, the positive sequence reactive component Q is considered to be when the phase locking is successful+And when the value is 0, obtaining the angular frequency omega through a PI controller, and obtaining the phase angle omega t through integration.
In the above embodiment, the voltage value U, the frequency f, the waveform signal, and the harmonic signal THD of the current photovoltaic power grid are obtained based on the multiple voltage sampling signals obtained by the Remote Terminal Unit (RTU);
and the edge computing terminal acquires steady-state data, transient-state data and switching state data of the power quality based on the voltage sampling signal, executes an edge computing process and analyzes the power quality.
Fig. 6 is a schematic diagram of a power quality assessment system used in the arrangements of fig. 1 and 2.
The edge computing terminal is configured with various load models, including a vehicle charging model, a user electricity utilization model, a photovoltaic model and a wind power model.
And the edge computing terminal is configured with various load models, and the power quality is predicted based on the various load models.
Fig. 7 is a preferred embodiment for performing power quality assessment.
On the basis of fig. 2, the edge computing terminal performs power quality analysis on the voltage sampling signal, and based on a result of the power quality analysis, performs a coordinate system transformation operation on the grid voltage signal, specifically including:
at the time of sampling i, a voltage sampling signal { U }ai，Ubi，UciAccess edge computing device Mi；
By the edge computing device MiCalculating the output load LiObtaining the output load set L ═ { L ═ L of all edge computing devices1，L2，......Ln}；
Judging whether the element values in the output load set L accord with uniform distribution within a preset range or not;
if not, executing coordinate system conversion operation of the power grid voltage signal, wherein the coordinate system conversion operation converts the three-phase power supply voltage value of the photovoltaic power grid into a two-dimensional voltage value under a two-phase static coordinate system;
and if so, returning to the step of sampling the grid voltage.
Fig. 8 is a diagram illustrating whether the element values shown in fig. 7 conform to a uniform distribution within a predetermined range.
The upper graph of FIG. 8 is for a case where the elements are uniformly distributed according to the standard, i.e., all elements are the same size; the lower graph of fig. 8 is a schematic diagram of the element values in the predetermined range conforming to the uniform distribution, that is, all the element sizes are within 5%, and it is determined that the element values in the predetermined range conform to the uniform distribution.
Fig. 9 shows the output result of the phase-locked loop according to the present invention, where the upper curve is a three-phase line voltage, harmonic and three-phase imbalance exist, and the three-phase imbalance condition is set as an extreme phase-loss condition. The following curve is a phase locking result of the power grid voltage, and it can be seen that the operation of phase locking is continuously performed in the phase-loss time period of the power grid voltage, when the phase-loss of the power grid voltage is recovered, after the phase-locking result of two periods slightly fluctuates, the phase-locking result is immediately recovered to be more normal, and the accuracy degree of phase locking can meet various requirements of the operation of the inverter.
In summary, the present invention at least solves the following technical problems:
the sampling value of the inverter software phase-locked loop is obtained by checking the voltage value of a power grid, and the problem that the phase-locked failure is caused due to the influence of voltage waveform distortion is easily caused;
the conversion formula of the inverter software phase-locked loop is too ideal, the voltage of a power grid in an actual system often has the condition of three-phase imbalance, and the problem of failure of the inverter phase-locked due to the three-phase imbalance of the voltage is solved;
the inverter operates in a system with a large harmonic ratio and three-phase imbalance, so that the problem of phase locking failure is caused;
in the process of low voltage ride through of the inverter, the phase of the power grid voltage cannot be accurately predicted when the power grid voltage is recovered, so that the problem of low voltage ride through failure is caused.
The technical scheme of the invention can at least achieve the following technical effects:
the remote terminal unit and the edge computing terminal are adopted to execute the electric energy computation of the sampling signal, so that the phase locking of the three-phase inverter suitable for the extreme electric energy quality condition can be adapted; after the novel phase-locking technology is adopted, the inverter can not be influenced by harmonic distortion of the power grid voltage when calculating the phase angle of the power grid voltage due to the introduction of a link of a generalized second-order integrator. After the novel phase-locking technology is adopted, because a double synchronous rotating coordinate system is introduced to carry out positive and negative sequence separation on the power grid voltage, the inverter can not be influenced by three-phase unbalance of the power grid voltage to a calculation result when the phase angle of the power grid voltage is calculated. After the novel phase locking technology is adopted, the inverter phase locking can not be influenced by the voltage and the power quality of a power grid, so that the phase locking failure probability is reduced. When the voltage of a power grid drops for a short time, low-voltage ride-through operation needs to be adopted by grid-connected equipment, and after the novel phase-locking technology is adopted, the low-voltage ride-through success rate is high.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims (10)

1. A phase locking method of a three-phase inverter suitable for extreme power quality conditions comprises a power grid voltage sampling step, a power grid voltage conversion step, a power grid voltage signal filtering step and a power grid voltage positive and negative sequence separation step;
the method is characterized in that:
in the power grid voltage sampling step, a plurality of Remote Terminal Units (RTUs) are used for sampling the voltage of the photovoltaic power grid for a plurality of times to obtain a plurality of voltage sampling signals;
the power grid voltage transformation step is to adopt a plurality of edge computing terminals to receive the voltage sampling signals, perform power quality analysis on the voltage sampling signals, and execute coordinate system transformation operation of the power grid voltage signals based on the result of the power quality analysis to obtain transformed power grid voltage signals;
in the power grid voltage filtering step, a generalized second-order integrator is adopted to filter harmonic signals of the converted power grid voltage signals;
the method comprises the following steps of performing positive and negative sequence separation on the power grid voltage by using a double synchronous rotating coordinate system method, removing a negative sequence component of the power grid voltage, and obtaining a three-phase balanced power grid voltage positive sequence component;
the method comprises the following steps that an edge computing terminal performs power quality analysis on the voltage sampling signal, and executes coordinate system transformation operation of the power grid voltage signal based on the result of the power quality analysis, and specifically comprises the following steps:
at the time of sampling i, a voltage sampling signal { U }ai，Ubi，UciAccess edge computing device Mi；
By the edge computing device MiCalculating the output load LiObtaining the output load set L ═ { L ═ L of all edge computing devices1，L2，......Ln}；
Judging whether the element values in the output load set L accord with uniform distribution within a preset range or not;
if not, executing coordinate system conversion operation of the power grid voltage signal, wherein the coordinate system conversion operation converts the three-phase power supply voltage value of the photovoltaic power grid into a two-dimensional voltage value under a two-phase static coordinate system;
and if so, returning to the step of sampling the grid voltage.
2. The phase locking method for the three-phase inverter applicable to the extreme power quality condition as claimed in claim 1, is characterized in that:
each of said Remote Terminal Units (RTU) is connected to one of said edge computing terminals.
3. The phase locking method for the three-phase inverter applicable to the extreme power quality condition as claimed in claim 1, is characterized in that:
the coordinate system transformation operation transforms a three-phase power supply voltage value of the photovoltaic power grid into a two-dimensional voltage value under a two-phase static coordinate system, and specifically comprises the following steps:
will three-phase network voltage UA、UB、UcTransforming the coordinate system into an alpha beta coordinate system of a rectangular coordinate system;
Figure FDA0002702683310000021
4. a phase locking method for a three-phase inverter suitable for extreme power quality conditions as claimed in claim 3, characterized by the following steps:
the method comprises the following steps of separating positive and negative sequences of the power grid voltage, separating the positive and negative sequences of the power grid voltage by using a double synchronous rotating coordinate system method, removing the negative sequence component of the power grid voltage, and obtaining the three-phase balanced positive sequence component of the power grid voltage, wherein the method specifically comprises the following steps:
decomposing the voltages alpha and beta under the transformed alpha and beta coordinate system into positive sequence, negative sequence and zero sequence values, wherein the zero sequence voltage is a common-mode component;
the positive sequence values are:
Figure FDA0002702683310000022
the negative sequence values are:
Figure FDA0002702683310000023
projecting the positive sequence value and the negative sequence value to obtain a direct current component D+、Q+And D-、Q-；
Wherein D +, Q + and D-, Q-satisfy the following conditions:
Figure FDA0002702683310000024
where ω is the angular frequency, t is the time variable, d+And d-The angle therebetween is 2 ω t.
5. The phase locking method for the three-phase inverter applicable to the extreme power quality condition as claimed in claim 1, is characterized in that:
each of said Remote Terminal Units (RTU) is connected to one of said edge computing terminals, further comprising:
acquiring a voltage value U, a frequency f, a waveform signal and a harmonic signal THD of the current photovoltaic power grid based on a plurality of voltage sampling signals acquired by the Remote Terminal Unit (RTU);
and the edge computing terminal collects the steady-state data, the transient-state data and the switching state data of the electric energy quality based on the voltage sampling signal and executes an edge computing process.
6. The phase locking method for the three-phase inverter applicable to the extreme power quality condition as claimed in claim 5 is characterized in that:
the edge computing terminal is configured with various load models including a vehicle charging model, a daily electricity model, a photovoltaic model and a wind power model.
7. The phase locking method for the three-phase inverter applicable to the extreme power quality condition as claimed in claim 5 is characterized in that:
and the edge computing terminal is configured with various load models, and the power quality is predicted based on the various load models.
8. A three-phase inverter phase-locking system suitable for use in extreme power quality conditions, the phase-locking system comprising a voltage signal sampling terminal, an edge calculation terminal, a transformation subsystem, a filtering subsystem, and a separation subsystem, for performing the three-phase inverter phase-locking method of any one of claims 1-7.
9. An evaluation system for power quality analysis, the evaluation system being connected with the three-phase inverter phase locking system suitable for extreme power quality conditions of claim 8, and being used for evaluating and predicting power instructions of a photovoltaic power grid.
10. A computer readable storage medium having stored thereon computer executable instruction code, the executable instruction code being executable by a memory and a processor for implementing the three phase inverter phase locking method of any one of claims 1 to 7.
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