CN116780609A - Control method and device of grid-connected converter system - Google Patents
Control method and device of grid-connected converter system Download PDFInfo
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Abstract
The disclosure provides a control method and device for a grid-connected converter system, wherein the control method comprises the following steps: acquiring a grid voltage of a grid connected with the grid-connected converter system, and extracting a positive sequence component, a negative sequence component and a harmonic component of the grid voltage; determining a reference current based on a preset reference power, a plurality of control coefficients, the positive sequence component, the negative sequence component and the harmonic component, wherein the plurality of control coefficients are used for weighting the positive sequence component, the negative sequence component and the harmonic component respectively; and controlling the output current of the grid-connected converter system based on the reference current. According to the control method and the control device of the grid-connected converter system, the problem that the electric energy quality is poor due to the fact that the existence of actual harmonic content is not considered in the existing grid-connected converter control method is solved, and the harmonic component can be adjusted through introducing the control coefficient so as to generate the reference current for controlling the output current of the grid-connected converter system.
Description
Technical Field
The present disclosure relates to the field of power electronics, and more particularly, to a method and apparatus for controlling a grid-connected inverter system.
Background
With the rapid development of renewable energy technologies, new energy grid-connected power generation capacity represented by photovoltaic and wind energy is increased year by year. However, high permeability of power electronics in new energy systems may lead to grid-tie reliability and stability problems. Grid code therefore requires that grid-tied power converter systems should be able to withstand grid voltage disturbances and short-term faults of a certain duration, and support restoration of grid operation by injecting a certain amount of active/reactive power to eliminate the voltage imbalance, also known as fault ride-through capability.
In the existing control method of the power electronic converter, positive and negative sequence voltage/current components in a power grid are mainly extracted, and decoupling control is performed to achieve specific control targets, such as public coupling point voltage support, power grid harmonic compensation, system overcurrent protection, instantaneous power flexible control and the like.
However, the influence of the actual harmonic content on the power quality in the fault ride-through process is not considered in the existing method, and the power quality is poor due to the existence of the harmonic.
Disclosure of Invention
In view of the problem that the existing grid-connected converter control method does not consider the existence of actual harmonic content and causes poor electric energy quality, the present disclosure provides a control method and device for a grid-connected converter system.
A first aspect of the present disclosure provides a control method of a grid-connected inverter system, the control method including: acquiring a grid voltage of a grid connected with the grid-connected converter system, and extracting a positive sequence component, a negative sequence component and a harmonic component of the grid voltage; determining a reference current based on a preset reference power, a plurality of control coefficients, the positive sequence component, the negative sequence component and the harmonic component, wherein the plurality of control coefficients are used for weighting the positive sequence component, the negative sequence component and the harmonic component respectively; and controlling the output current of the grid-connected converter system based on the reference current.
Optionally, the step of determining the reference current based on a preset reference power, control coefficient, positive sequence component, negative sequence component and harmonic component comprises: determining an initial reference current based on the reference power, the positive sequence component, the negative sequence component, and the harmonic component; based on the plurality of control coefficients, the positive sequence component, the negative sequence component, and the harmonic component contained in the initial reference current are weighted and summed to determine the reference current.
Optionally, the initial reference current has a partial expression form, wherein the step of determining the reference current includes: filtering out fluctuating components in denominator terms of the initial reference current, and based on the plurality of control coefficients, weighting and summing the positive sequence component, the negative sequence component and the harmonic component in the denominator terms of the initial reference current, thereby obtaining the reference current.
Optionally, the step of extracting the positive sequence component, the negative sequence component and the harmonic component of the grid voltage comprises: converting the grid voltage into two-phase voltage under a static coordinate system; and carrying out decoupling filtering on the two-phase voltage, and extracting the positive sequence component, the negative sequence component and the harmonic component.
Optionally, the reference current comprises a two-phase reference current in a stationary coordinate system, wherein the step of controlling the output current of the grid-connected inverter system based on the reference current comprises: transforming the two-phase reference current in the stationary coordinate system into an actual three-phase reference current; and controlling the output current of the grid-connected converter system based on the three-phase reference current.
Optionally, the reference power includes an active reference power and a reactive reference power, and the control coefficient includes a positive sequence control coefficient, a negative sequence control coefficient, and a harmonic control coefficient, wherein a sum of the positive sequence control coefficient and the negative sequence control coefficient is zero, and a ratio of one of the positive sequence control coefficient and the negative sequence control coefficient to the harmonic control coefficient is greater than or equal to a ratio of the reactive reference power to the active reference power.
Optionally, the control coefficients include a first control coefficient for weighted summation of a positive sequence component, a negative sequence component and a harmonic component corresponding to one phase reference current of the two-phase reference currents, and a second control coefficient for weighted summation of a positive sequence component, a negative sequence component and a harmonic component corresponding to the other phase reference current of the two-phase reference currents, wherein the first control coefficient is in a proportional relationship with the second control coefficient.
Optionally, the first control coefficient includes a first positive sequence control coefficient, a first negative sequence control coefficient, and a first harmonic control coefficient, the second control coefficient includes a second positive sequence control coefficient, a second negative sequence control coefficient, and a second harmonic control coefficient, wherein a sum of the first positive sequence control coefficient and the first negative sequence control coefficient is zero, and a sum of the second positive sequence control coefficient and the second negative sequence control coefficient is zero, wherein the first positive sequence control coefficient is in a proportional relationship with the second positive sequence control coefficient, the first negative sequence control coefficient is in a proportional relationship with the second harmonic control coefficient, and a ratio of the first positive sequence control coefficient to the first harmonic control coefficient is greater than or equal to a ratio of the reactive reference power to the active reference power, wherein a sum of the first positive sequence control coefficient, the first negative sequence control coefficient, the second harmonic control coefficient, and the first harmonic control coefficient are each 1, and the second harmonic control coefficient take a positive sequence control range of 1.
Optionally, the step of controlling the output current of the grid-connected inverter system based on the reference current comprises: acquiring the current output current of the grid-connected converter system; determining a current difference between the reference current and the current output current based on the reference current and the current output current; and controlling the output current of the grid-connected converter system by modulating the current difference value.
A second aspect of the present disclosure provides a control apparatus of a grid-connected inverter system, the control apparatus including: an extraction unit for obtaining a grid voltage of a grid connected with the grid-connected converter system and extracting a positive sequence component, a negative sequence component and a harmonic component of the grid voltage; a determining unit configured to determine a reference current based on a preset reference power, a plurality of control coefficients, the positive sequence component, the negative sequence component, and the harmonic component, wherein the plurality of control coefficients are used to weight the positive sequence component, the negative sequence component, and the harmonic component, respectively; and the control unit is used for controlling the output current of the grid-connected converter system based on the reference current.
Optionally, the control device is disposed in a main controller of the grid-connected inverter system.
A third aspect of the present disclosure provides a computer readable storage medium, which when executed by at least one processor, causes the at least one processor to perform a method of controlling a grid-tie inverter system according to the present disclosure.
A fourth aspect of the present disclosure provides a computer device comprising: at least one processor; at least one memory storing computer-executable instructions, wherein the computer-executable instructions, when executed by the at least one processor, cause the at least one processor to perform a method of controlling a grid-tie inverter system according to the present disclosure.
The control method and the control device of the grid-connected converter system can adjust positive sequence, negative sequence and harmonic components of voltage by introducing control coefficients so as to generate reference current for controlling the output current of the grid-connected converter system, so that the output current of the grid-connected converter system can meet the preset standard.
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In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present disclosure, the drawings that are required to be used in the embodiments will be briefly described below, and it should be understood that the following drawings only illustrate the exemplary embodiments of the present disclosure and therefore should not be construed as limiting the scope of the present disclosure.
Fig. 1 is a schematic flowchart illustrating a control method of a grid-tied inverter system according to an exemplary embodiment of the present disclosure.
Fig. 2 is a schematic flow chart showing steps of determining a reference current in a control method of a grid-connected inverter system according to an exemplary embodiment of the present disclosure.
Fig. 3 is a functional block diagram illustrating an example of a control method of a grid-tied inverter system according to an exemplary embodiment of the present disclosure.
Fig. 4 is a grid-tied inverter system grid voltage waveform diagram illustrating an example of a control method of a grid-tied inverter system according to an exemplary embodiment of the present disclosure.
Fig. 5 is a grid-tied inverter system point of common coupling voltage waveform diagram illustrating an example of a control method of a grid-tied inverter system according to an exemplary embodiment of the present disclosure.
Fig. 6 is a grid-connected inverter system grid-connected current waveform diagram illustrating an example of a control method of the grid-connected inverter system according to an exemplary embodiment of the present disclosure.
Fig. 7A to 10B are schematic diagrams illustrating total harmonic content of a grid-connected inverter system at different grid-connected current magnitudes according to an example of a control method of the grid-connected inverter system according to an exemplary embodiment of the present disclosure.
Fig. 11 is a waveform diagram illustrating extraction of harmonic components from grid-connected current of a grid-connected inverter system according to an example of a control method of the grid-connected inverter system according to an exemplary embodiment of the present disclosure.
Fig. 12 is a schematic block diagram illustrating a control apparatus of a grid-tied inverter system according to an exemplary embodiment of the present disclosure.
Fig. 13 is a schematic block diagram illustrating a computer device according to an exemplary embodiment of the present disclosure.
Detailed Description
The following detailed description is provided to assist the reader in obtaining a thorough understanding of the methods, apparatus, and/or systems described herein. However, various changes, modifications, and equivalents of the methods, apparatus, and/or systems described herein will be apparent after an understanding of the present disclosure. For example, the order of operations described herein is merely an example and is not limited to those set forth herein, but may be altered as will be apparent after an understanding of the disclosure of the application, except for operations that must occur in a specific order. Furthermore, descriptions of features known in the art may be omitted for clarity and conciseness.
The features described herein may be embodied in different forms and should not be construed as limited to the examples described herein. Rather, the examples described herein have been provided to illustrate only some of the many possible ways to implement the methods, devices, and/or systems described herein that will be apparent after an understanding of the present disclosure.
As used herein, the term "and/or" includes any one of the listed items associated as well as any combination of any two or more.
Although terms such as "first," "second," and "third" may be used herein to describe various elements, components, regions, layers or sections, these elements, components, regions, layers or sections should not be limited by these terms. Rather, these terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first member, first component, first region, first layer, or first portion referred to in the examples described herein may also be referred to as a second member, second component, second region, second layer, or second portion without departing from the teachings of the examples.
In the description, when an element (such as a layer, region or substrate) is referred to as being "on" another element, "connected to" or "coupled to" the other element, it can be directly "on" the other element, be directly "connected to" or be "coupled to" the other element, or one or more other elements intervening elements may be present. In contrast, when an element is referred to as being "directly on" or "directly connected to" or "directly coupled to" another element, there may be no other element intervening elements present.
The terminology used herein is for the purpose of describing various examples only and is not intended to be limiting of the disclosure. Singular forms also are intended to include plural forms unless the context clearly indicates otherwise. The terms "comprises," "comprising," and "having" specify the presence of stated features, amounts, operations, components, elements, and/or combinations thereof, but do not preclude the presence or addition of one or more other features, amounts, operations, components, elements, and/or combinations thereof.
Unless defined otherwise, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs after understanding this disclosure. Unless explicitly so defined herein, terms (such as those defined in a general dictionary) should be construed to have meanings consistent with their meanings in the context of the relevant art and the present disclosure, and should not be interpreted idealized or overly formal.
In addition, in the description of the examples, when it is considered that detailed descriptions of well-known related structures or functions will cause a ambiguous explanation of the present disclosure, such detailed descriptions will be omitted.
It should be noted that, before the present application proposes, the influence of the actual harmonic content on the power quality in the fault ride through process is not considered in the existing method, and the existence of the harmonic will result in poor power quality.
In particular, in one approach, specific fault ride-through control objectives may be achieved based on different current reference objectives, but the approach does not take into account the effect of harmonics in the actual grid on current control. In another scheme, the fault ride-through flexible control scheme under the condition of unbalanced grid voltage drop can be optimized continuously so as to realize the power quality adjustment and the grid supporting capacity improvement of the power electronic converter, but the scheme still does not consider the influence of the actual harmonic content on the stability of the system in the fault ride-through process.
In addition, the positive and negative sequence current and the line impedance of the power electronic converter can be decoupled and analyzed under the condition of unbalanced power grid voltage, and the active current and reactive current components of the system are injected into the power grid at the same time so as to improve the grid connection stability of the system. This approach, while eliminating power electronic converter output current harmonics, causes system power oscillations, while the control algorithm requires the use of many notch or low pass filters, which can lead to reference phase delays and control errors. In addition, when the grid voltage contains a large amount of low-order harmonics, current harmonics and active and reactive power ripples in the system are significantly increased, and stable output of the system is still not facilitated.
In view of this, exemplary embodiments according to the present disclosure provide a control method of a grid-connected inverter system, a control apparatus of a grid-connected inverter system, a computer-readable storage medium, and a computer device to solve at least one of the above problems.
According to a first aspect of the present disclosure, a control method of a grid-connected inverter system is provided. Fig. 1 shows a schematic flow chart of a control method of a grid-connected inverter system according to an exemplary embodiment of the present disclosure. As shown in fig. 1, a control method of a grid-connected inverter system according to an exemplary embodiment of the present disclosure may include the steps of:
in step S10, a grid voltage of a grid connected to the grid-connected inverter system may be obtained, and a positive sequence component, a negative sequence component, and a harmonic component of the grid voltage may be extracted.
In this step, the grid voltage may be obtained by sampling the grid by a device such as a voltage hall sensor, where the grid voltage may be a three-phase voltage, and thus, after the grid voltage is obtained, the grid voltage may be converted into two-phase voltages in a stationary coordinate system, and the positive sequence component, the negative sequence component, and the harmonic component may be extracted by performing decoupling filtering on the two-phase voltages.
As an example, it may be based on a three-phase grid voltage v a 、v b And v c The two-phase voltage v under the static coordinate system is obtained through Clarke transformation α And v β It can then be fed into a decoupling filter to extract the positive sequence components of the two-phase voltages, respectivelyAndnegative sequence component->And->Harmonic component->And->
Specifically, the Clarke transformation process of the voltage can be as shown in the following formula (1):
wherein the two-phase voltage v α And v β Can be represented by the following formula (2):
here, the transfer function of the decoupling filter can be represented by the following (3):
wherein v is α/β Expressed as phase voltage v α Or v β ；ω 0 The working frequency of the decoupling filter can be the working frequency of a power grid; omega c A cut-off frequency (also referred to as a cut-off frequency) that is a decoupling filter; h represents the harmonic order, in an exemplary embodiment of the present disclosure, calculations may be performed for medium and low order harmonics, such as shown belowIn the examples, the 5 th order, the 7 th order, the 11 th order and the 13 th order harmonics can be calculated for higher harmonics, for example, the harmonics can be calculated for any number of harmonics according to practical application requirements.
In step S20, a reference current may be determined based on a preset reference power, a plurality of control coefficients, a positive sequence component, a negative sequence component, and a harmonic component.
Here, a plurality of control coefficients may be used to weight the positive sequence component, the negative sequence component, and the harmonic component, respectively. In particular, the control coefficient may be used to adjust the magnitude of the corresponding voltage component. For example, by varying the magnitude of the control coefficient used to weight the harmonic components, the harmonic content in the reference current may be constrained, the smaller the harmonic content, the better the power quality in the actual output current.
As an example, as shown in fig. 2, step S20 may include:
in step S21, an initial reference current may be determined based on the reference power, the positive sequence component, the negative sequence component, and the harmonic component.
Here, the initial reference current and the finally determined reference current may each include two-phase reference currents in a stationary coordinate system, in which case in step S21, a rated power predetermined by the grid-connected system may be used as a reference power, which may be adjusted as needed according to different systems and different operation states of the same system. The initial reference current can be represented by the following (4):
wherein, the liquid crystal display device comprises a liquid crystal display device,representing the phase voltage v α Corresponding one-phase initial reference current, +.>Representing the phase voltage v β Corresponding another phase initial parameter Current of examination, P 0 Representing the reference power, h= -5,7, -11,13 represents the calculation of the 5 th, 7 th, 11 th and 13 th harmonic components, however, this is only an example, and h may be calculated taking any number of harmonics according to the actual application needs.
As an example, for equation (4) above, the initial reference current in the stationary coordinate system may be further derived from the instantaneous power theory in which the reference power may include an active reference power and a reactive reference power, each phase of the initial reference current may be decomposed into an active initial reference current and a reactive initial reference current, each phase of the reference current may be decomposed into an active reference current and a reactive reference current, and in particular, the initial reference current may be represented by the following (5):
wherein, the liquid crystal display device comprises a liquid crystal display device,representing the phase voltage v α Active initial reference current of corresponding one-phase initial reference current, +.>Representing the phase voltage v α Reactive initial reference current of the corresponding one-phase initial reference current; />Representing the phase voltage v β Active initial reference current of the corresponding other phase initial reference current, +.>Representing the phase voltage v β Reactive initial reference current of the corresponding another phase initial reference current; p (P) * Represents active reference power, Q * Representing reactive reference power, the sum of the active reference power and the reactive reference power may be the reference power P described above 0 。
Referring back to fig. 2, at step S22, the positive sequence component, the negative sequence component, and the harmonic component contained in the initial reference current may be weighted-summed based on a plurality of control coefficients to determine the reference current of the parallel converter.
According to an exemplary embodiment of the present disclosure, the control coefficient may be determined based on the reference power, for example, may be determined based on the active reference power and the reactive reference power described above.
As shown in the above-described formulas (4) and (5), the initial reference current has a partial expression form, and thus, in this step S22, the step of determining the reference current may further include: and filtering fluctuation components in denominator terms of the initial reference current, and carrying out weighted summation on positive sequence components, negative sequence components and harmonic components in the denominator terms of the initial reference current based on a plurality of control coefficients so as to obtain the reference current.
In particular, on the one hand, when the initial reference current is in a partial form, harmonic components in its denominator can be filtered out, so that fourier expansion can be facilitated in the calculation. Since the harmonic component in the denominator has very little influence on the magnitude of the initial reference current, and the existence of the harmonic component in the denominator complicates the calculation process, the filtering processing can improve the calculation speed and efficiency on the premise of ensuring the calculation accuracy.
The process of filtering the ripple component will be described below by taking equations (4) and (5) as examples, and the expression of the initial reference current may have denominator terms thereinThe denominator term may be expressed as a constant component +.>And wave component->The form of the addition, i.e.,thus, denominator term->Can be represented by the following formula (6):
wherein V is h Representing the amplitude of all harmonic components, V m And V n Respectively represent the amplitudes of different harmonic components, theta m Representation and amplitude V m Initial phase angle of corresponding harmonic component, θ n Representation and amplitude V n The initial phase angle of the corresponding harmonic component, where h takes 1 to represent the positive sequence component of the fundamental wave, e.g., 50Hz, and h takes-1 to represent the negative sequence component of the fundamental wave, e.g., 50Hz.
As an example, the above-described process of filtering out the fluctuating component may be implemented by a filter, for example, a low-pass filter may be used.
The above describes the process of filtering out the fluctuating component in the denominator term of the initial reference current, in which step S22, on the other hand, the positive sequence component, the negative sequence component and the harmonic component in the molecular term of the initial reference current may also be weighted summed based on a plurality of control coefficients.
Specifically, the control coefficients may include a positive sequence control coefficient for weighting positive sequence components in the initial reference current, a negative sequence control coefficient for weighting negative sequence components in the initial reference current, and a harmonic control coefficient for weighting harmonic components in the initial reference current.
Here, the control coefficient may satisfy a predetermined constraint relation, specifically, the sum of the positive sequence control coefficient and the negative sequence control coefficient may be zero, and the ratio of one of the positive sequence control coefficient and the negative sequence control coefficient to the harmonic control coefficient is greater than or equal to the ratio of the reactive reference power to the active reference power, which will be described in detail below in connection with examples.
When the initial reference current and the reference current are two-phase currents, the control coefficients may include a first control coefficient for weighted summation of a positive sequence component, a negative sequence component, and a harmonic component corresponding to one of the two-phase reference currents, and a second control coefficient for weighted summation of a positive sequence component, a negative sequence component, and a harmonic component corresponding to the other of the two-phase reference currents, where the first control coefficient and the second control coefficient may be in a proportional relationship.
Taking equation (5) above as an example, the fluctuating component in the denominator term of the initial reference current may be filtered out, and the positive sequence component, the negative sequence component, and the harmonic component in the molecular term of the initial reference current, which is the two-phase current, may be weighted by introducing the first control coefficient and the second control coefficient.
Here, the first control coefficient may include a first positive sequence control coefficient, a first negative sequence control coefficient, and a first harmonic control coefficient, and the second control coefficient may include a second positive sequence control coefficient, a second negative sequence control coefficient, and a second harmonic control coefficient.
Specifically, the reference current can be represented by the following (7):
wherein, the liquid crystal display device comprises a liquid crystal display device,for the first positive sequence control coefficient, +.>For the first negative sequence control coefficient, +.>For the first harmonic control coefficient,for the second positive sequence control coefficient, +.>For the second negative sequence control coefficient, +.>For the second harmonic control factor,/->Representing the phase voltage v α Active reference current of corresponding one-phase reference current, +.>Representing the phase voltage v α Reactive reference current of the corresponding one-phase reference current, < >>Representing the phase voltage v β Active reference current of the corresponding other phase reference current, +.>Representing the phase voltage v β Reactive reference current of the corresponding another phase reference current.
Here, the value ranges of each of the first positive sequence control coefficient, the first negative sequence control coefficient, the first harmonic control coefficient, the second positive sequence control coefficient, the second negative sequence control coefficient and the second harmonic control coefficient may be [ -1,1], and thus, the total amplitude of the reference current weighted by each control coefficient may be ensured to be unchanged.
In an exemplary embodiment of the present disclosure, the sum of the first positive sequence control coefficient and the first negative sequence control coefficient may be zero, and the sum of the second positive sequence control coefficient and the second negative sequence control coefficient may be zero.
Taking the formula (7) as an example, the following formula (8) may be satisfied between control coefficients:
further, in an exemplary embodiment of the present disclosure, the first positive sequence control coefficient may be in a proportional relationship with the second positive sequence control coefficient, the first negative sequence control coefficient may be in a proportional relationship with the second negative sequence control coefficient, and the first harmonic control coefficient may be in a proportional relationship with the second harmonic control coefficient.
Taking the formula (7) as an example, the following formula (9) may be satisfied between control coefficients:
here, T is a proportional matrix between two-phase control coefficients.
It should be noted that the proportional matrix T between the control coefficients of the formula (9) is derived from the three-phase grid voltage and the two-phase voltage transformation relationship under the Clarke transformed stationary coordinate system, so as to facilitate calculation, and other phase voltage transformation manners may be adopted in the present disclosure, and in different transformation manners, a specific constraint relationship exists between the two-phase voltages, which may be determined by coordinate system transformation.
As can be seen from the above expression (8) and expression (9), in the case where the ratio between the control coefficients is constrained and the sum of the positive sequence control coefficient and the negative sequence control coefficient can be zero, if any one of the first positive sequence control coefficient, the first negative sequence control coefficient, the second positive sequence control coefficient, and the second negative sequence control coefficient, and the first harmonic control coefficient or the second harmonic control coefficient are known, the values of all six control coefficients can be determined.
Here, any one of the first positive sequence control coefficient, the first negative sequence control coefficient, the second positive sequence control coefficient, and the second negative sequence control coefficient may satisfy a predetermined proportional relationship with the first harmonic control coefficient or the second harmonic control coefficient.
Specifically, taking the example of formula (9) as an example, the first positive sequence control coefficientControl coefficient with first harmonic>May be greater than or equal to the reactive reference power Q * And active reference power P * Ratio of (2), i.e. satisfy the relation->Here, due to reactive reference power Q * And active reference power P * Can be determined according to grid-connected standards of the power grid, so that the total harmonic (TotalHarmonic Distortion, THD) content in the three-phase reference current can be corrected by the above relation.
Thus, based on the formulas (8) and (9) and relative to the reactive reference power Q * And active reference power P * Allowing only one control coefficient to be input during control (e.g., the first positive sequence control coefficient described herein) All other control coefficients can be determined, so that the convenience of control and the efficiency of executing control are improved.
As described above, according to the exemplary embodiments of the present disclosure, the total harmonic content of the three-phase reference current may be corrected according to the grid-connection standard of the power grid, specifically, since the control coefficient is used to adjust the amplitude of the reference current, the larger the amplitude is, the smaller the harmonic content in the reference current is, the better the power quality is, by reasonably selecting the current positive sequence/negative sequence control coefficient and the harmonic control coefficient to inject into the power grid based on the reference power, the voltage harmonic content of the grid-connection public coupling point may be limited from being too high, and exceeding the standard of grid-connection of the power grid.
In step S30, the output current of the grid-connected inverter system may be controlled based on the reference current.
Based on the reference currents determined in step S20 described above, in case the reference currents comprise two-phase reference currents in a stationary coordinate system, the two-phase reference currents may be transformed back to three-phase reference currents.
Specifically, the two-phase reference currents in the stationary coordinate system may be transformed into actual three-phase reference currents; and controlling the output current of the grid-connected converter system based on the three-phase reference current.
Taking the Clarke transformation example described above, the two-phase reference current may be subjected to Clarke inverse transformation, specifically, the inverse transformation process may be represented by the following formula (10):
wherein, the liquid crystal display device comprises a liquid crystal display device,and->Respectively representing three phase reference currents.
Thus, the above formula (7) is substituted into formula (10), and the actual three-phase reference current of the grid-connected inverter represented by formula (11) is obtained by arrangementAnd->
Based on the reference current determined in the above manner, the step of controlling the output current of the grid-connected inverter system may include: acquiring the current output current of a grid-connected converter system; determining a current difference between the reference current and the present output current based on the reference current and the present output current; the output current of the grid-connected inverter system is controlled by modulating the current difference.
Specifically, the present output current of the grid-connected inverter system may be sampled using a device such as a current hall sensor and then subtracted from a reference current (e.g., the three-phase reference current described above), respectively, to obtain a current difference. The current difference may be fed into a proportional resonant (Proportional Resonant, PR) regulator (also referred to as PR controller) and a space vector pulse width (Space Vector Pulse Width Modulation, SVPWM) modulation module in sequence to generate control signals that control the output current of the grid-tied inverter system, which may be, for example, six drive signals that drive the switching tubes of the grid-tied inverter.
Here, the PR modulator may have a transfer function as shown in the following equation (12):
wherein k is p To adjust the proportionality coefficient, k r For the resonance coefficient ω is the angular frequency of resonance.
Fig. 3 illustrates a schematic diagram of an example of a control method of a grid-tied inverter system according to an exemplary embodiment of the present disclosure.
As shown in fig. 3, three-phase voltage v a 、v b And v c The two-phase voltage v can be obtained by transforming a coordinate system α And v β Positive sequence components can then be extracted from the two-phase voltages, respectivelyAnd->Negative sequence component->And->Harmonic component->And->Then, a reference power, such as active reference power P, may be obtained * And reactive reference power Q * And selecting a control coefficient according to the reference power>And +.>Thus, two-phase reference currents +.A grid-connected converter can be generated based on the positive sequence component, the negative sequence component, the harmonic component and the reference power>And->The two-phase reference current can be inversely transformed to obtain three-phase reference current +.> And->And three-phase reference current +.>And->And the current output current i of the grid-connected converter abc Inputting into PR controller, according to the current difference, SVPWM outputs drive signal S for regulating switching tube of grid-connected converter 1 To S 6 To adjust the output current of the grid-connected converter, the adjusted input current can be close to or be the reference currentA current.
According to the exemplary embodiment of the disclosure, by introducing the control coefficients of the positive and negative sequence components and the harmonic components of the grid voltage, calculating the reference current and controlling the actual output current of the grid-connected converter system based on the reference current, the total harmonic content and the amplitude of the output current in the output current of the grid-connected converter system can be decoupled, that is, the total harmonic content is unchanged no matter how the amplitude of the output current is, so that the electric energy quality can be improved, the grid-connected electric energy quality of a public coupling point can be effectively improved, the grid-connected guide electric energy quality requirement can be met, the safe starting of the system can be ensured, and the controllability and the reliability of the system can be improved. In addition, the control method according to the exemplary embodiment of the disclosure is simple to calculate, easy to implement in engineering, high in response speed and beneficial to system control in practical application.
Simulation results of a control method to which the grid-connected inverter system according to an exemplary embodiment of the present disclosure is applied will be analyzed in detail below with reference to fig. 4 to 11 to present effectiveness and advantages of the control method.
Simulation parameters of the system can be given, wherein the dc bus voltage of the grid-connected converter system can be 400V, the ac grid voltage can be 170V, as shown in fig. 4 and 5, assuming that a C-type fault with an imbalance of 0.3 occurs at a time of 0.1s, and contains 4% of 5 th harmonic and 3% of 7 th harmonic, THD is 5%, the active power of the power electronic converter is 0.6kW, the reactive power is 1.2kVar, the system can employ LCL-type filters with LCL parameters of 5mH, 27uF and 3.6mH, respectively, and the switching frequency of the system can be 10kHz. In fig. 4 and 5, the solid line represents the a-phase in the three-phase voltage, the dotted line and the dashed line represent the b-phase and the c-phase in the three-phase voltage, respectively, and as can be seen in fig. 4 and 5, at time 0.1s, the b-phase and the c-phase voltages drop.
After the fault occurs, the amplitude of the reference current of the grid-connected inverter is reduced every 0.1s by adjusting the power, and as shown in fig. 6, the amplitudes of 0.1s to 0.2s, 0.2s to 0.3s, 0.3s to 0.4s, and 0.4s to 0.5s are sequentially reduced. At the moment, the system can adjust the harmonic content in the grid-connected current by introducing the control coefficient, so that the decoupling of THD and current amplitude is realized, the percentage of THD is unchanged under different current reference amplitudes, and the requirement of grid-connected power quality is met.
Specifically, as shown in fig. 7A to 10B, fig. 7A, 8A, 9A and 10A show waveform diagrams of the a-phase current in the grid-connected current of the grid-connected inverter system, in which the region indicated by a thick solid line in each diagram is the present analysis region, and fig. 7B, 8B, 9B and 10B show THD analysis diagrams in the time corresponding to the analysis regions shown in fig. 7A, 8A, 9A and 10A, respectively.
As can be seen from fig. 7A, the selected signal is 25 cycles in total, and the window of fourier transform (FFT) is selected to be 2 cycles, i.e., the portion indicated by the thick solid line, in the time of 0.1s to 0.2s, wherein it can be seen from fig. 7B that the fundamental wave is 50Hz, the fundamental wave amplitude is 4.412, and the thd is 4.62%, which are mainly derived from the 5 th harmonic and the 7 th harmonic.
As can be seen from fig. 8A, the selected signal is 25 cycles in total, and the window of the fourier transform (FFT) is selected to be 2 cycles, i.e., the part indicated by the thick solid line, in the time of 0.2s to 0.3s, wherein it can be seen from fig. 8B that the fundamental wave is 50Hz, the fundamental wave amplitude is 3.522, and the thd is still 4.62%, which is mainly derived from the 5 th harmonic and the 7 th harmonic.
As can be seen from fig. 9A, the selected signal is 25 cycles in total, and the window of fourier transform (FFT) is selected to be 2 cycles, i.e., the part indicated by the thick solid line, in the time of 0.3s to 0.4s, wherein it can be seen from fig. 9B that the fundamental wave is 50Hz, the fundamental wave amplitude is 2.201, and the thd is still 4.62%, which is mainly derived from the 5 th harmonic and the 7 th harmonic.
As can be seen from fig. 10A, the selected signal is 25 cycles in total, and the window of fourier transform (FFT) is selected to be 2 cycles, i.e., the part indicated by the thick solid line, in the time of 0.4s to 0.5s, wherein it can be seen from fig. 10B that the fundamental wave is 50Hz, the fundamental wave amplitude is 1.321, and the thd is still 4.62%, which is mainly derived from the 5 th harmonic and the 7 th harmonic.
As can be seen from fig. 7A to fig. 10B, when the fundamental wave amplitude is changed, THD is 4.62%, and the grid-connected power quality requirement can be satisfied. Here, since fig. 7A to 10B are mainly shown for the purpose of analyzing the change of harmonics with the amplitude of Fundamental waves, in fig. 7B, 8B, 9B and 10B, the vertical axis is a percentage Mag (% of amplitude of Fundamental waves) with respect to the amplitude of Fundamental waves (i.e., mag (% of Fundamental)), in dimensionless units, and the horizontal axis is a spectrum of current, in hertz (Hz).
Fig. 11 shows a waveform schematic of the grid-tied current extraction harmonic components of the grid-tied converter system. As can be seen from fig. 11, by setting different control coefficients, the 5 th harmonic and the 7 th harmonic in the current can be reduced along with the reduction of the current amplitude, but the THD of the grid-connected current is unchanged, so that the magnitude of the harmonic component is decoupled from the total output current amplitude, that is, when the amplitude of the total output current is changed, the ratio of the harmonic component in the total amplitude can be ensured to be unchanged, thereby improving the power quality of the grid-connected public coupling point and meeting the power quality requirement of the grid-connected guidance rule.
Therefore, according to the fault ride-through control method of the grid-connected converter system, which is described in the specification, the output current amplitude and the total harmonic content (THD) of the power electronic converter can be decoupled simply, conveniently and efficiently, the grid-connected power quality of a public coupling point can be effectively improved, the grid-connected guide-way power quality requirement is met, the safe starting of the system is ensured, and the controllability and the reliability of the system are improved.
According to a second aspect of the present disclosure, a control device for a grid-connected inverter system is provided. As shown in fig. 12, the control device of the grid-connected inverter system includes an extraction unit 100, a determination unit 200, and a control unit 300.
The extraction unit 100 may be configured to obtain a grid voltage of a grid connected to the grid-connected converter system and extract a positive sequence component, a negative sequence component and a harmonic component of the grid voltage.
The determining unit 200 may be configured to determine the reference current based on a preset reference power, a plurality of control coefficients for weighting the positive sequence component, the negative sequence component, and the harmonic component, respectively.
The control unit 300 may be configured to control the output current of the grid-connected inverter system based on the reference current.
As an example, the control device of the grid-connected inverter system may be provided in the main controller of the grid-connected inverter system.
As an example, the determination unit 200 may be further configured to: determining an initial reference current based on the reference power, the positive sequence component, the negative sequence component, and the harmonic component; the positive sequence component, the negative sequence component, and the harmonic component contained in the initial reference current are weighted and summed based on a plurality of control coefficients to determine the reference current.
As an example, the initial reference current has a divided expression form, in which case the determination unit 200 may be further configured to: and filtering fluctuation components in denominator terms of the initial reference current, and carrying out weighted summation on positive sequence components, negative sequence components and harmonic components in the denominator terms of the initial reference current based on a plurality of control coefficients so as to obtain the reference current.
As an example, the determination unit 200 may be further configured to: converting the power grid voltage into two-phase voltage under a static coordinate system; and (3) decoupling and filtering are carried out through the two-phase voltage, and positive sequence components, negative sequence components and harmonic components are extracted.
As an example, the reference currents comprise two-phase reference currents in a stationary coordinate system, in which case the control unit 300 may be further configured to: transforming the two-phase reference current in the static coordinate system into an actual three-phase reference current; and controlling the output current of the grid-connected converter system based on the three-phase reference current.
As an example, the reference power includes an active reference power and a reactive reference power, and the control coefficients include a positive sequence control coefficient, a negative sequence control coefficient, and a harmonic control coefficient, wherein a sum of the positive sequence control coefficient and the negative sequence control coefficient is zero, wherein a ratio of one of the positive sequence control coefficient and the negative sequence control coefficient to the harmonic control coefficient is greater than or equal to a ratio of the reactive reference power to the active reference power.
As an example, the control coefficients include a first control coefficient for weighted summation of a positive sequence component, a negative sequence component, and a harmonic component corresponding to one of the two phases of reference currents, and a second control coefficient for weighted summation of a positive sequence component, a negative sequence component, and a harmonic component corresponding to the other of the two phases of reference currents, wherein the first control coefficient is proportional to the second control coefficient.
As an example, the first control coefficient includes a first positive sequence control coefficient, a first negative sequence control coefficient, and a first harmonic control coefficient, and the second control coefficient includes a second positive sequence control coefficient, a second negative sequence control coefficient, and a second harmonic control coefficient, wherein a sum of the first positive sequence control coefficient and the first negative sequence control coefficient is zero, a sum of the second positive sequence control coefficient and the second negative sequence control coefficient is zero, wherein the first positive sequence control coefficient is in a proportional relationship with the second positive sequence control coefficient, the first negative sequence control coefficient is in a proportional relationship with the second negative sequence control coefficient, and the first harmonic control coefficient is in a proportional relationship with the second harmonic control coefficient, wherein a ratio of the first positive sequence control coefficient to the first harmonic control coefficient is greater than or equal to a ratio of reactive reference power to active reference power, and wherein a value range of each of the first positive sequence control coefficient, the first negative sequence control coefficient, the first harmonic control coefficient, the second positive sequence control coefficient, the second negative sequence control coefficient, and the second harmonic control coefficient is [ -1,1].
As an example, the control unit 300 may be further configured to: acquiring the current output current of a grid-connected converter system; determining a current difference between the reference current and the present output current based on the reference current and the present output current; the output current of the grid-connected inverter system is controlled by modulating the current difference.
According to a third aspect of the present disclosure, there is provided a computer readable storage medium, which when executed by at least one processor, causes the at least one processor to perform a method of controlling a grid-tie inverter system according to the first aspect of the present disclosure.
The control method of the grid-connected inverter system according to the embodiments of the present disclosure may be written as a computer program and stored on a computer-readable storage medium. Examples of the computer readable storage medium include: read-only memory (ROM), random-access programmable read-only memory (PROM), electrically erasable programmable read-only memory (EEPROM), random-access memory (RAM), dynamic random-access memory (DRAM), static random-access memory (SRAM), flash memory, nonvolatile memory, CD-ROM, CD-R, CD + R, CD-RW, CD+RW, DVD-ROM, DVD-R, DVD + R, DVD-RW, DVD+RW, DVD-RAM, BD-ROM, BD-R, BD-R LTH, BD-RE, blu-ray or optical disk storage, hard Disk Drives (HDD), solid State Disks (SSD), card memory (such as multimedia cards, secure Digital (SD) cards or ultra-fast digital (XD) cards), magnetic tape, floppy disks, magneto-optical data storage, hard disks, solid state disks, and any other means configured to store computer programs and any associated data, data files and data structures in a non-transitory manner and to provide the computer programs and any associated data, data files and data structures to a processor or computer to enable the processor or computer to execute the programs. In one example, the computer program and any associated data, data files, and data structures are distributed across networked computer systems such that the computer program and any associated data, data files, and data structures are stored, accessed, and executed in a distributed manner by one or more processors or computers.
According to a fourth aspect of the present disclosure, a computer device is provided. As shown in fig. 13, the computer device 1 includes: at least one processor 101; at least one memory 102 storing computer-executable instructions, wherein the computer-executable instructions, when executed by the at least one processor, cause the at least one processor to perform a method of controlling a grid-tie inverter system according to the first aspect of the present disclosure.
By way of example, the computer device 1 may be a PC computer, tablet device, personal digital assistant, smart phone, or other device capable of executing the above-described set of instructions. Here, the computer device 1 is not necessarily a single electronic device, but may be any apparatus or a collection of circuits capable of executing the above-described instructions (or instruction set) individually or in combination. The computer device 1 may also be part of an integrated control system or system manager, or may be configured as a portable electronic device that interfaces with either locally or remotely (e.g., via wireless transmission).
In the computer apparatus 1, the processor 101 may include a Central Processing Unit (CPU), a Graphics Processor (GPU), a programmable logic device, a dedicated processor system, a microcontroller, or a microprocessor. By way of example, and not limitation, processors may also include analog processors, digital processors, microprocessors, multi-core processors, processor arrays, network processors, and the like.
The processor 101 may execute instructions or code stored in the memory 102, wherein the memory 102 may also store data. The instructions and data may also be transmitted and received over a network via a network interface device, which may employ any known transmission protocol.
The memory 102 may be integrated with the processor 101, for example, RAM or flash memory disposed within an integrated circuit microprocessor or the like. In addition, memory 501 may include a stand-alone device, such as an external disk drive, a storage array, or other storage device usable by any database system. The memory 102 and the processor 101 may be operatively coupled or may communicate with each other, for example, through an I/O port, a network connection, etc., such that the processor 101 is able to read files stored in the memory.
In addition, the computer device 1 may also include a video display (such as a liquid crystal display) and a user interaction interface (such as a keyboard, mouse, touch input device, etc.). All components of the computer device 1 may be connected to each other via a bus and/or a network.
While certain embodiments have been shown and described, it would be appreciated by those skilled in the art that changes and modifications may be made to these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.
Claims (13)
1. A control method of a grid-connected inverter system, the control method comprising:
acquiring a grid voltage of a grid connected with the grid-connected converter system, and extracting a positive sequence component, a negative sequence component and a harmonic component of the grid voltage;
determining a reference current based on a preset reference power, a plurality of control coefficients, the positive sequence component, the negative sequence component and the harmonic component, wherein the plurality of control coefficients are used for weighting the positive sequence component, the negative sequence component and the harmonic component respectively;
and controlling the output current of the grid-connected converter system based on the reference current.
2. The control method of a grid-connected inverter system according to claim 1, wherein the step of determining the reference current based on a preset reference power, a control coefficient, the positive sequence component, the negative sequence component, and the harmonic component comprises:
determining an initial reference current based on the reference power, the positive sequence component, the negative sequence component, and the harmonic component;
based on the plurality of control coefficients, the positive sequence component, the negative sequence component, and the harmonic component contained in the initial reference current are weighted and summed to determine the reference current.
3. The method for controlling a grid-connected inverter system according to claim 2, wherein the initial reference current has a divided expression,
wherein the step of determining the reference current comprises:
filtering out fluctuating components in denominator terms of the initial reference current, and based on the plurality of control coefficients, weighting and summing the positive sequence component, the negative sequence component and the harmonic component in the denominator terms of the initial reference current, thereby obtaining the reference current.
4. A control method of a grid-connected inverter system according to any one of claims 1 to 3, wherein the step of extracting the positive sequence component, the negative sequence component, and the harmonic component of the grid voltage comprises:
converting the grid voltage into two-phase voltage under a static coordinate system;
and carrying out decoupling filtering on the two-phase voltage, and extracting the positive sequence component, the negative sequence component and the harmonic component.
5. The method for controlling a grid-tied inverter system according to claim 4, wherein the reference current comprises a two-phase reference current in a stationary coordinate system,
wherein the step of controlling the output current of the grid-connected inverter system based on the reference current comprises:
Transforming the two-phase reference current in the stationary coordinate system into an actual three-phase reference current;
and controlling the output current of the grid-connected converter system based on the three-phase reference current.
6. The method for controlling a grid-tied inverter system according to claim 5, wherein the reference power comprises an active reference power and a reactive reference power, the control coefficients comprise a positive sequence control coefficient, a negative sequence control coefficient and a harmonic control coefficient,
wherein the sum of the positive sequence control coefficient and the negative sequence control coefficient is zero,
wherein a ratio of one of the positive sequence control coefficient and the negative sequence control coefficient to the harmonic control coefficient is greater than or equal to a ratio of the reactive reference power to the active reference power.
7. The method for controlling a grid-connected inverter system according to claim 6, wherein the control coefficients include a first control coefficient and a second control coefficient,
wherein the first control coefficient is used for weighted summation of positive sequence component, negative sequence component and harmonic component corresponding to one phase reference current in the two-phase reference currents, the second control coefficient is used for weighted summation of positive sequence component, negative sequence component and harmonic component corresponding to the other phase reference current in the two-phase reference currents,
Wherein the first control coefficient is in direct proportion to the second control coefficient.
8. The method of claim 7, wherein the first control coefficients comprise a first positive sequence control coefficient, a first negative sequence control coefficient, and a first harmonic control coefficient, the second control coefficients comprise a second positive sequence control coefficient, a second negative sequence control coefficient, and a second harmonic control coefficient,
wherein the sum of the first positive sequence control coefficient and the first negative sequence control coefficient is zero, the sum of the second positive sequence control coefficient and the second negative sequence control coefficient is zero,
wherein the first positive sequence control coefficient and the second positive sequence control coefficient are in a direct proportion relation, the first negative sequence control coefficient and the second negative sequence control coefficient are in a direct proportion relation, the first harmonic control coefficient and the second harmonic control coefficient are in a direct proportion relation,
wherein the ratio of the first positive sequence control coefficient to the first harmonic control coefficient is greater than or equal to the ratio of the reactive reference power to the active reference power,
wherein the value range of each of the first positive sequence control coefficient, the first negative sequence control coefficient, the first harmonic control coefficient, the second positive sequence control coefficient, the second negative sequence control coefficient and the second harmonic control coefficient is [ -1,1].
9. The method of controlling a grid-connected inverter system according to claim 1, wherein the step of controlling an output current of the grid-connected inverter system based on the reference current comprises:
acquiring the current output current of the grid-connected converter system;
determining a current difference between the reference current and the current output current based on the reference current and the current output current;
and controlling the output current of the grid-connected converter system by modulating the current difference value.
10. A control device for a grid-connected inverter system, the control device comprising:
an extraction unit for obtaining a grid voltage of a grid connected with the grid-connected converter system and extracting a positive sequence component, a negative sequence component and a harmonic component of the grid voltage;
a determining unit configured to determine a reference current based on a preset reference power, a plurality of control coefficients, the positive sequence component, the negative sequence component, and the harmonic component, wherein the plurality of control coefficients are used to weight the positive sequence component, the negative sequence component, and the harmonic component, respectively;
and the control unit is used for controlling the output current of the grid-connected converter system based on the reference current.
11. The control device of a grid-tied inverter system according to claim 10, wherein the control device is provided in a main controller of the grid-tied inverter system.
12. A computer readable storage medium, characterized in that instructions in the computer readable storage medium, when executed by at least one processor, cause the at least one processor to perform the control method of the grid-tie converter system of any one of claims 1-9.
13. A computer device, comprising:
at least one processor;
at least one memory storing computer-executable instructions,
wherein the computer executable instructions, when executed by the at least one processor, cause the at least one processor to perform the method of controlling a grid-tie inverter system as claimed in any one of claims 1-9.
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