CN111342645A - Grid-connected inverter low-frequency harmonic current control method and device - Google Patents

Grid-connected inverter low-frequency harmonic current control method and device Download PDF

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CN111342645A
CN111342645A CN202010220454.5A CN202010220454A CN111342645A CN 111342645 A CN111342645 A CN 111342645A CN 202010220454 A CN202010220454 A CN 202010220454A CN 111342645 A CN111342645 A CN 111342645A
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CN111342645B (en
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杨凯
王兴
张伟健
辜承林
李健
熊飞
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Huazhong University of Science and Technology
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    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H02M1/126—Arrangements for reducing harmonics from ac input or output using passive filters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics

Abstract

The invention discloses a method and a device for controlling low-frequency harmonic current of a grid-connected inverter, wherein the method comprises the following steps: acquiring a current state equation of the L-type three-phase grid-connected inverter in a dq coordinate system, wherein the current state equation comprises a grid voltage disturbance term, a variable coupling term and a model parameter deviation term; sampling three-phase current and obtaining d-axis and q-axis components of the three-phase current through coordinate transformation; estimating the power grid voltage disturbance term, the variable coupling term and the model parameter deviation term as unknown disturbance, and calculating the control quantity of a d axis and a q axis by using the estimated value of the unknown disturbance; performing active disturbance rejection control on the d-axis and q-axis components of the three-phase current according to the control quantity of the d-axis and q-axis; the invention not only saves the feedforward and decoupling steps when the controller is designed, so that the controller has strong robustness to system parameter change and model deviation, but also improves the performance of the controller in the aspects of current tracking speed, unbalanced current and low-frequency harmonic current suppression.

Description

Grid-connected inverter low-frequency harmonic current control method and device
Technical Field
The invention belongs to the technical field of grid-connected inverter control, and particularly relates to a low-frequency harmonic current control method and device for a grid-connected inverter.
Background
With the decreasing of the amount of conventional fossil energy resources represented by petroleum and natural gas and the global environmental problems caused by the use of non-clean energy resources, new energy resources represented by solar energy and wind energy are widely developed and used on a global scale. The grid-connected inverter is used as the last-stage power conversion equipment of the grid connection of the distributed power generation system based on new energy, and plays a key role in controlling grid-connected electric energy.
Among various topological structures of the grid-connected inverter, the voltage source type three-phase inverter with the L filtering is widely applied due to the advantages of simple structure, bidirectional energy flow, three-phase balanced power transmission to a power grid and the like. Because the power grid has strict requirements on the quality of the electric energy output by the inverter, the research on the current controller is of great significance.
When the traditional controller is used for controlling grid-connected current, various control strategies need to be adopted to solve the problems of grid voltage disturbance, variable coupling, model parameter deviation and the like, so that the design difficulty and complexity are increased, and ideal effects are difficult to obtain in the aspects of dynamic response speed, control of low-frequency harmonic current and three-phase unbalanced current.
Disclosure of Invention
Aiming at least one defect or improvement requirement in the prior art, the invention provides a method and a device for controlling low-frequency harmonic current of a grid-connected inverter.
To achieve the above object, according to a first aspect of the present invention, there is provided a grid-connected inverter low-frequency harmonic current control method, including:
acquiring a current state equation of the L-type three-phase grid-connected inverter in a dq coordinate system, wherein the current state equation comprises a grid voltage disturbance term, a variable coupling term and a model parameter deviation term;
sampling three-phase current and obtaining d-axis and q-axis components of the three-phase current through coordinate transformation;
estimating the power grid voltage disturbance term, the variable coupling term and the model parameter deviation term as unknown disturbance, and calculating the control quantity of a d axis and a q axis by using the estimated value of the unknown disturbance; and performing active disturbance rejection control on the d-axis and q-axis components of the three-phase current according to the control quantity of the d-axis and q-axis.
Preferably, in the method for controlling low-frequency harmonic current of a grid-connected inverter, the obtaining of a current state equation of the L-type three-phase grid-connected inverter in the dq coordinate system specifically includes:
constructing a current state equation of the L-shaped three-phase grid-connected inverter in a natural coordinate system;
and carrying out coordinate transformation on the current state equation by taking the direction of the grid voltage synthetic vector as the positive direction of the d axis to respectively obtain a d-axis current state equation and a q-axis current state equation.
Preferably, in the method for controlling low-frequency harmonic current of a grid-connected inverter, the current state equation of the L-type three-phase grid-connected inverter in a natural coordinate system is specifically as follows:
Figure BDA0002425885280000021
in the formula, L 'and R' are approximate values of actual inductance and impedance respectively; i.e. ia,ib,icThree-phase current which is merged into a power grid respectively; e.g. of the typea,eb,ecRespectively the three-phase voltage of the power grid; u. ofa,ub,ucThe three-phase voltage output by the inverter is respectively; f. ofa,fb,fcRespectively are model deviation terms in a three-phase current state equation;
preferably, in the method for controlling low-frequency harmonic current of a grid-connected inverter, the state equations of d-axis current and q-axis current are respectively as follows:
Figure BDA0002425885280000022
in the formula id,iqD-axis and q-axis components of a three-phase composite current merged into a power grid; e.g. of the typed,eqRespectively are d-axis components and q-axis components of the three-phase synthetic voltage of the power grid; u. ofd,uqD-axis and q-axis components of the three-phase composite voltage output by the inverter respectively; f. ofd,fqModel bias terms in the d-axis and q-axis current state equations, respectively.
Preferably, the method for controlling the low-frequency harmonic current of the grid-connected inverter, wherein the calculating the controlled variable of the d-axis and the q-axis by using the estimated value of the unknown disturbance specifically includes:
acquiring d-axis and q-axis components of output voltage of the inverter, and constructing an extended state observer by using the d-axis and q-axis components of the output voltage and the d-axis and q-axis components of three-phase current;
estimating d-axis and q-axis components of the three-phase current and unknown disturbance by using the extended state observer to obtain respective corresponding estimated values;
respectively taking the difference between a given d-axis current and the estimated value of the d-axis component and the difference between a given q-axis current and the estimated value of the q-axis component to obtain d-axis and q-axis current errors;
and forming the control quantity of the d axis and the q axis by utilizing the linear feedback corresponding to the current errors of the d axis and the q axis and the compensation quantity corresponding to the estimation value of the unknown disturbance.
Preferably, in the method for controlling low-frequency harmonic current of a grid-connected inverter, the obtaining of the d-axis and q-axis components of the output voltage of the inverter specifically includes:
the method for reconstructing the voltage is adopted to obtain d-axis and q-axis components of the actual output voltage of the inverter, and the corresponding calculation equation is as follows:
Figure BDA0002425885280000031
in the formula, T2s/2rA transformation matrix representing a two-phase stationary coordinate system to a two-phase rotating coordinate system; u shapedcRepresents the dc bus voltage; t issRepresents a switching cycle; t is ta,tb,tcAnd respectively representing the conduction time of upper switching tubes of three-phase bridge arms A, B and C in the previous switching period.
Preferably, the method for controlling the low-frequency harmonic current of the grid-connected inverter, wherein the step of performing active disturbance rejection control on the d-axis and q-axis components of the three-phase current according to the d-axis and q-axis control quantities specifically includes:
converting the controlled variables of the d axis and the q axis into controlled variables in a two-phase static coordinate system through inverse Park conversion, carrying out pulse width modulation on the converted controlled variables to obtain a switching tube driving signal, and inputting the switching tube driving signal into an inverter to carry out active disturbance rejection control on the d axis and the q axis components of grid-connected current.
According to the second aspect of the present invention, there is also provided a grid-connected inverter low-frequency harmonic current control apparatus, including:
the acquisition unit is used for acquiring a current state equation of the L-type three-phase grid-connected inverter in a dq coordinate system, wherein the current state equation comprises a power grid voltage disturbance term, a variable coupling term and a model parameter deviation term;
the conversion unit is used for carrying out coordinate transformation on the acquired three-phase current to obtain d-axis and q-axis components of the three-phase current;
the self-reactive interference control unit is used for estimating the power grid voltage disturbance item, the variable coupling item and the model parameter deviation item as unknown disturbance, and calculating the control quantity of a d axis and a q axis by using the estimated value of the unknown disturbance; and performing active disturbance rejection control on the d-axis component and the q-axis component of the three-phase current according to the control quantity of the d-axis component and the control quantity of the q-axis component respectively.
Preferably, the grid-connected inverter low-frequency harmonic current control device further includes a voltage reconstruction unit;
the voltage reconstruction unit is used for acquiring d-axis and q-axis components of the output voltage of the inverter by adopting a voltage reconstruction method.
Preferably, in the grid-connected inverter low-frequency harmonic current control device, the self-reactive interference control unit includes:
the estimation module is used for constructing an extended state observer by using d-axis and q-axis components of the output voltage and d-axis and q-axis components of the three-phase current; estimating d-axis and q-axis components of the three-phase current and unknown disturbance by using the extended state observer to obtain respective corresponding estimated values;
the first calculation module is used for respectively obtaining the difference between a given d-axis current and the estimated value of the d-axis component and the difference between a given q-axis current and the estimated value of the q-axis component to obtain d-axis and q-axis current errors;
and the second calculation module is used for forming the control quantity of the d axis and the q axis by utilizing the linear feedback corresponding to the current errors of the d axis and the q axis and the compensation quantity corresponding to the estimation value of the unknown disturbance.
Preferably, in the low-frequency harmonic current control device of the grid-connected inverter, the self-reactance interference control unit further includes a modulation module;
the modulation module is used for converting the control quantity of the d axis and the q axis into the control quantity in a two-phase static coordinate system through inverse Park conversion, carrying out pulse width modulation on the converted control quantity to obtain a switching tube driving signal, and inputting the switching tube driving signal into an inverter to carry out active disturbance rejection control on the d axis and the q axis components of grid-connected current.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
according to the grid-connected inverter low-frequency harmonic current control method and device, the network voltage disturbance, variable coupling, model parameter deviation and other factors are used as unknown disturbance to carry out synchronous estimation, and the influence of the factors on current control can be compensated; compared with the traditional method, the method does not need separate feedforward and decoupling steps when the controller is designed, simplifies the design process of the controller, and enables the controller to have strong robustness to system parameter change and model deviation. Meanwhile, the performance of the system in the aspects of current tracking speed, unbalanced current and low-frequency harmonic current suppression is also improved.
Drawings
Fig. 1 is a flowchart of a method for controlling low-frequency harmonic current of a grid-connected inverter according to an embodiment of the present invention;
fig. 2 is a topology structure diagram of an L-filter voltage source type three-phase grid-connected inverter according to an embodiment of the present invention;
FIG. 3 is a block diagram of active disturbance rejection control of the d-axis component of a three-phase current provided by an embodiment of the present invention;
fig. 4 is a logic block diagram of a low-frequency harmonic current control device of a grid-connected inverter according to an embodiment of the present invention;
fig. 5 is a system block diagram of a grid-connected inverter low-frequency harmonic current control device according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Example one
Fig. 1 is a flowchart of a method for controlling low-frequency harmonic current of a grid-connected inverter provided in this embodiment, and as shown in fig. 1, the method specifically includes the following steps:
s1, obtaining a current state equation of the L-type three-phase grid-connected inverter in a dq coordinate system, wherein the current state equation comprises a grid voltage disturbance term, a variable coupling term and a model parameter deviation term; the method specifically comprises the following two substeps:
s11, considering model deviation, and establishing a current state equation of the L-shaped three-phase grid-connected inverter in a natural coordinate system;
with reference to L filtering as shown in figure 2Topological structure diagram of voltage source type three-phase grid-connected inverter, LI,RIRespectively representing a filter inductor and a line resistor on the output side of the inverter; l isG,RGRespectively representing equivalent inductance and resistance which are connected in series when the device is connected to the grid. In the mathematical model of the inverter, the inductance L comprises LI,LGAnd leakage inductance of the grid-connected transformer, wherein the resistor R comprises RI,RGAnd a transformer coil resistance.
And recording L 'and R' as approximate values of the impedance parameters L and R respectively, and establishing a current state equation of the L-type three-phase grid-connected inverter in a natural coordinate system according to a voltage-current basic relation of the circuit as follows:
Figure BDA0002425885280000061
in the formula, L 'and R' are approximate values of actual impedance parameters respectively; i.e. ia,ib,icThree-phase current which is merged into a power grid respectively; e.g. of the typea,eb,ecRespectively the three-phase voltage of the power grid; u. ofa,ub,ucThe three-phase voltage output by the inverter is respectively; f. ofa,fb,fcRespectively, the model deviations in the three-phase current state equation.
Due to the grid-connected impedance LG,RGIt is difficult to obtain accurate impedance parameters L, R when actually designing the controller, the impedance parameters are represented by approximate values L ', R' in the mathematical model, and the model deviation is additionally represented as a variable fa,fb,fcThe mathematical model thus established is more realistic.
S12, taking the direction of the grid voltage synthesis vector as the positive direction of the d axis, and obtaining a current state equation in the dq coordinate system through coordinate transformation;
the coordinate system of the current state equation is converted into a dq coordinate system from a natural coordinate system, the fundamental wave alternating current in the original natural coordinate system can be converted into direct current, and the design of a controller is facilitated; and the decoupling control of the grid-connected active power and reactive power can be easily realized by taking the direction of the grid voltage synthetic vector as the positive direction of the d axis, namely the d axis component of the current controls the grid-connected active power, and the q axis component of the current controls the grid-connected reactive power.
In particular, according to the sampled three-phase voltage e of the power grida,eb,ecAnd obtaining the direction theta of a grid voltage synthetic vector after the processing of the phase-locked loop, wherein the direction theta is used as the positive direction of a d axis, and a q axis leads the d axis by 90 degrees, so as to establish a dq rotation coordinate system. The current state equation in the dq coordinate system obtained by coordinate transformation is:
Figure BDA0002425885280000071
in the formula id,iqD-axis and q-axis components of a three-phase composite current, respectively, that is incorporated into the grid; e.g. of the typed,eqRespectively are d-axis and q-axis components of the three-phase composite voltage of the power grid; u. ofd,uqD-axis and q-axis components of the three-phase composite voltage output by the inverter, respectively; f. ofd,fqModel deviations in the d-axis and q-axis current state equations, respectively;
in the d-axis current state equation, -edL' is the grid back-emf term, ω iqIs a q-axis coupling term, fdIs a model bias term, -R' id/L' is the voltage drop;
in the q-axis current state equation, -eqthe/L' is a counter potential term of the power grid, -omega idIs a d-axis coupling term, fqIs a model bias term, -R' iqand/L' is the voltage drop.
S2, sampling the three-phase current and obtaining d-axis and q-axis components of the three-phase current through coordinate transformation;
specifically, sampling three-phase current i output by the invertera,ib,icThen converting the three-phase current into a current i in the dq coordinate system by coordinate conversiond,iq；
Obtaining the current i in the dq coordinate systemd,iqIs the basis for estimating state variables, unknown disturbances, and implementing current closed-loop control.
S3, obtaining the actual output power of the inverter by adopting a voltage reconstruction methodPress ua,ub,ucThe corresponding calculation equation is as follows:
Figure BDA0002425885280000081
in the formula, T2s/2rA transformation matrix representing a two-phase stationary coordinate to a two-phase rotating coordinate; u shapedcRepresents the dc bus voltage; t issRepresents a switching cycle; t is ta,tb,tcAnd respectively representing the conduction time of upper switching tubes of three-phase bridge arms A, B and C in the previous switching period.
The method for reconstructing the voltage is adopted to obtain the d-axis and q-axis components of the output voltage of the inverter, the method can ensure that the voltage used in the extended state observer is always an actual value, and compared with a method using a voltage command value, the method has the advantages that: when the voltage instruction value exceeds the maximum output voltage of the inverter in the dynamic process, the estimation effect of the variable and the control effect of the current can be ensured not to be influenced.
S4, estimating power grid voltage disturbance, dq axis cross coupling and model deviation as unknown disturbance, and performing active disturbance rejection control on d-axis and q-axis components of the current respectively;
in particular, with d-axis component i to the currentdControl is taken as an example for explanation, and power grid voltage disturbance, q-axis cross coupling, model deviation and the like are carried out according to a current state equation of a d axis, namely (-R' i)d/L'+ωiq-ed/L'+fd) As an unknown disturbance; in particular, the model deviation includes not only the parameter deviation in the current state equation but also all factors not considered in modeling, such as three-phase impedance asymmetry, harmonic components of voltage current, and the like.
First of all with an output voltage ua,ub,ucD-axis component u ofdAnd three-phase current ia,ib,icD-axis component i ofdConstructing an extended state observer; recording the unknown disturbance as x2dUsing extended state observer pair idAnd x2dAnd (6) estimating. Root of herbaceous plantAccording to a current state equation of a d axis and a correlation theory of the extended state observer, the designed expression of the second-order linear extended state observer is as follows:
Figure BDA0002425885280000082
in the formula, z1d,z2dAre respectively idAnd x2dAn estimated value of (d); b0Represents a control gain, and b0＝1/L'；β1,β2Representing the error gain factor.
The second order linear extended state observer is represented by id,udAs an input, z can be implemented by setting a suitable error gain factor1d,z2dTo idAnd x2dAnd obtaining corresponding estimation values.
According to given d-axis current
Figure BDA0002425885280000091
And z1dCalculating d-axis current error, wherein the designed linear feedback expression is as follows:
Figure BDA0002425885280000092
in the formula, kpA scaling factor representing linear feedback.
A control quantity u obtained according to the linear feedback0dAnd an estimate z of said unknown disturbance2dAnd calculating to obtain d-axis control quantity after compensating disturbance
Figure BDA0002425885280000093
Control based on d-axis
Figure BDA0002425885280000094
Performing active disturbance rejection control on the d-axis component of the three-phase current; the d-axis control quantity
Figure BDA0002425885280000095
The expression of (a) is:
Figure BDA0002425885280000096
fig. 3 is a block diagram of active disturbance rejection control of d-axis component of current, in which expressions g(s), h(s) are respectively:
Figure BDA0002425885280000097
from fig. 3, in combination with the principle of active disturbance rejection control, it is easy to understand that: a controller to
Figure BDA0002425885280000098
And idFor input, a control quantity is output without considering the estimation error of the disturbance
Figure BDA0002425885280000099
Disturbance compensation quantity-z contained in2dExactly the unknown disturbance x can be completely compensated2dTherefore, the originally complex control object is equivalent to a pure integrator series system.
Except for the parameter control gain b0In addition, the design of the d-axis current controller is independent of model parameters, which makes the controller robust to system parameter variations.
Similarly, according to the current state equation of the q axis, the design process of the d-axis current controller is referred to, and then the design of the q-axis current controller can be completed.
Control quantity output by d-axis and q-axis current controllers
Figure BDA00024258852800000910
Conversion into a controlled variable in a two-phase stationary coordinate system by inverse Park transformation
Figure BDA00024258852800000911
And then, obtaining six paths of switching tube driving signals by adopting an SVPWM (space vector pulse width modulation) method, thereby realizing active disturbance rejection control of d-axis and q-axis components of grid-connected current.
Example two
The embodiment provides a low-frequency harmonic current control device of a grid-connected inverter, which can be realized in a software and/or hardware mode and can be integrated on electronic equipment; fig. 4 is a logic block diagram of the grid-connected inverter low-frequency harmonic current control device provided in this embodiment, see fig. 4, and the control device includes an obtaining unit, a converting unit, a voltage reconstructing unit, and an auto-disturbance rejection control unit; wherein:
the acquisition unit is used for acquiring a current state equation of the L-type three-phase grid-connected inverter in a dq coordinate system, wherein the current state equation comprises a power grid voltage disturbance term, a variable coupling term and a model parameter deviation term; specifically, the method comprises the following steps: firstly, constructing a current state equation of the L-shaped three-phase grid-connected inverter in a natural coordinate system according to the circuit topology of the L-shaped three-phase grid-connected inverter and by combining the voltage and current basic relation of a circuit; and then according to the sampled three-phase voltage of the power grid, utilizing a phase-locked loop PLL to obtain the direction theta of a power grid voltage synthetic vector, and performing coordinate transformation on the current state equation by taking the direction theta of the power grid voltage synthetic vector as the positive direction of the d axis to respectively obtain a d-axis current state equation and a q-axis current state equation. For the current state equation of the L-type three-phase grid-connected inverter in the natural coordinate system and the dq rotation coordinate system, refer to the first embodiment, and details are not described here.
The conversion unit is used for carrying out coordinate transformation on the acquired three-phase current to obtain d-axis and q-axis components of the three-phase current;
firstly, a three-phase current i merged into a power grid is collected through a current samplera,ib,icThe conversion unit is used for combining the direction theta of the vector to the three-phase current i based on the grid voltagea,ib,icPerforming coordinate transformation to convert it into current i in the dq coordinate systemd,iq(ii) a Obtaining the current i in the dq coordinate systemd,iqIs the basis for estimating state variables, unknown disturbances, and implementing current closed-loop control.
The voltage reconstruction unit is used for acquiring d-axis and q-axis components of the output voltage of the inverter by adopting a voltage reconstruction method; and d-axis and q-axis components of the output voltage are used for constructing an extended state observer in the follow-up process, and then the d-axis and q-axis components and unknown disturbance of the three-phase current are estimated through the extended state observer.
The self-reactive interference control unit is used for estimating a power grid voltage disturbance item, a variable coupling item and a model parameter deviation item as unknown disturbance, and calculating the control quantity of a d axis and a q axis by using the estimated value of the unknown disturbance; performing active disturbance rejection control on the d-axis component and the q-axis component of the three-phase current according to the control quantity of the d-axis component and the q-axis component respectively;
as a preferred example of this embodiment, the self-interference rejection control unit specifically includes an estimation module, a first calculation module, a second calculation module, and a modulation module;
the estimation module is used for constructing an extended state observer by using d-axis and q-axis components of the output voltage and d-axis and q-axis components of the three-phase current; estimating d-axis and q-axis components of the three-phase current and unknown disturbance by using the extended state observer to obtain respective corresponding estimated values;
this embodiment operates on the d-axis component i of the currentdFirst, the estimation module uses the d-axis component u of the output voltage as an example to explain the controldAnd d-axis component i of three-phase currentdConstructing an extended state observer; recording the unknown disturbance as x2dUsing extended state observer pair idAnd x2dCarrying out estimation; according to the d-axis current state equation and the relevant theory of the extended state observer, the expression of the second-order linear extended state observer provided by the embodiment is as follows:
Figure BDA0002425885280000111
in the formula, z1d,z2dAre respectively idAnd x2dAn estimated value of (d); b0Represents a control gain, and b0＝1/L'；β1,β2Representing the error gain factor.
The second order linear extended state observer is represented by id,udAs an input, z can be implemented by setting a suitable error gain factor1d,z2dTo idAnd x2dIs trackedAnd obtaining corresponding estimated values.
The first calculation module is used for respectively obtaining the difference between a given d-axis current and the estimated value of the d-axis component and the difference between a given q-axis current and the estimated value of the q-axis component to obtain d-axis and q-axis current errors; specifically, the method comprises the following steps:
the first calculation module is used for calculating the current according to the given d-axis current
Figure BDA0002425885280000112
And z1dCalculating d-axis current error, wherein the designed linear feedback expression is as follows:
Figure BDA0002425885280000113
in the formula, kpA scaling factor representing linear feedback.
The second calculation module is used for forming the control quantity of the d axis and the q axis by utilizing the linear feedback corresponding to the current errors of the d axis and the q axis and the compensation quantity corresponding to the estimation value of the unknown disturbance;
specifically, the second calculation module obtains the control quantity u according to linear feedback0dAnd an estimate z of the unknown disturbance2dObtaining d-axis control quantity after compensating disturbance
Figure BDA0002425885280000114
Control based on d-axis
Figure BDA0002425885280000115
Performing active disturbance rejection control on the d-axis component of the three-phase current; the d-axis control quantity
Figure BDA0002425885280000116
The expression of (a) is:
Figure BDA0002425885280000117
the modulation module is used for converting the controlled variables of the d axis and the q axis into controlled variables in a two-phase static coordinate system through inverse Park conversion, performing pulse width modulation on the converted controlled variables by adopting an SVPWM (space vector pulse width modulation) method to obtain a switching tube driving signal, and inputting the switching tube driving signal into an inverter to perform active disturbance rejection control on the d axis and the q axis components of grid-connected current.
Fig. 5 is a system block diagram of the low-frequency harmonic current control device of the grid-connected inverter provided in this embodiment, the upper part of the diagram is a main circuit of an L-type three-phase grid-connected inverter, and the lower part of the diagram is a component of the low-frequency harmonic current control device of the grid-connected inverter, and referring to fig. 5, the control device mainly includes a voltage/current sampler, a phase-locked loop, a coordinate conversion unit, a voltage reconstruction unit, an active disturbance rejection controller (d-axis, q-axis ADRC controller), an SVPWM modulation module, and the like. The grid-connected active power and reactive power can be respectively controlled by setting the current given values of the d axis and the q axis.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. A grid-connected inverter low-frequency harmonic current control method is characterized by comprising the following steps:
acquiring a current state equation of the L-type three-phase grid-connected inverter in a dq coordinate system, wherein the current state equation comprises a grid voltage disturbance term, a variable coupling term and a model parameter deviation term;
sampling three-phase current and obtaining d-axis and q-axis components of the three-phase current through coordinate transformation;
estimating the power grid voltage disturbance term, the variable coupling term and the model parameter deviation term as unknown disturbance, and calculating the control quantity of a d axis and a q axis by using the estimated value of the unknown disturbance; and performing active disturbance rejection control on the d-axis and q-axis components of the three-phase current according to the control quantity of the d-axis and q-axis.
2. The method for controlling low-frequency harmonic current of the grid-connected inverter according to claim 1, wherein the obtaining of the current state equation of the L-type three-phase grid-connected inverter in the dq coordinate system specifically comprises:
constructing a current state equation of the L-shaped three-phase grid-connected inverter in a natural coordinate system;
and carrying out coordinate transformation on the current state equation by taking the direction of the grid voltage synthetic vector as the positive direction of the d axis to respectively obtain a d-axis current state equation and a q-axis current state equation.
3. The grid-connected inverter low-frequency harmonic current control method according to claim 2, wherein a current state equation of the L-type three-phase grid-connected inverter in a natural coordinate system is specifically as follows:
Figure FDA0002425885270000011
in the formula, L 'and R' are approximate values of actual inductance and impedance respectively; i.e. ia,ib,icThree-phase currents which are respectively merged into a power grid; e.g. of the typea,eb,ecThe three-phase voltages of the power grid are respectively; u. ofa,ub,ucThree-phase voltages output by the inverters respectively; f. ofa,fb,fcRespectively are model deviation terms in a three-phase current state equation;
the d-axis current state equation and the q-axis current state equation are respectively as follows:
Figure FDA0002425885270000021
in the formula id,iqD-axis and q-axis components of three-phase synthetic current merged into a power grid respectively; e.g. of the typed,eqRespectively are d-axis components and q-axis components of the three-phase synthetic voltage of the power grid; u. ofd,uqD-axis and q-axis components of the three-phase composite voltage output by the inverter respectively; f. ofd,fqThe model deviation terms in the d-axis current state equation and the q-axis current state equation are respectively.
4. The method for controlling the low-frequency harmonic current of the grid-connected inverter according to claim 1, wherein the step of calculating the controlled variables of the d axis and the q axis by using the estimated value of the unknown disturbance specifically comprises the steps of:
acquiring d-axis and q-axis components of output voltage of the inverter, and constructing an extended state observer by using the d-axis and q-axis components of the output voltage and the d-axis and q-axis components of three-phase current;
estimating d-axis and q-axis components of the three-phase current and unknown disturbance by using the extended state observer to obtain respective corresponding estimated values;
respectively taking the difference between a given d-axis current and the estimated value of the d-axis component and the difference between a given q-axis current and the estimated value of the q-axis component to obtain d-axis and q-axis current errors;
and forming the control quantity of the d axis and the q axis by utilizing the linear feedback corresponding to the current errors of the d axis and the q axis and the compensation quantity corresponding to the estimation value of the unknown disturbance.
5. The grid-connected inverter low-frequency harmonic current control method according to claim 4, wherein the d-axis and q-axis components for obtaining the output voltage of the inverter are specifically:
the method for reconstructing the voltage is adopted to obtain d-axis and q-axis components of the actual output voltage of the inverter, and the corresponding calculation equation is as follows:
Figure FDA0002425885270000022
in the formula, T2s/2rA transformation matrix representing a two-phase stationary coordinate system to a two-phase rotating coordinate system; u shapedcRepresents the dc bus voltage; t issRepresents a switching cycle; t is ta,tb,tcAnd respectively representing the conduction time of upper switching tubes of three-phase bridge arms A, B and C in the previous switching period.
6. The method for controlling the low-frequency harmonic current of the grid-connected inverter according to claim 1, wherein the step of performing active disturbance rejection control on d-axis and q-axis components of three-phase current according to the d-axis and q-axis control quantities specifically comprises the steps of:
converting the controlled variables of the d axis and the q axis into controlled variables in a two-phase static coordinate system through inverse Park conversion, carrying out pulse width modulation on the converted controlled variables to obtain a switching tube driving signal, and inputting the switching tube driving signal into an inverter to carry out active disturbance rejection control on the d axis and the q axis components of grid-connected current.
7. A grid-connected inverter low-frequency harmonic current control device is characterized by comprising:
the acquisition unit is used for acquiring a current state equation of the L-type three-phase grid-connected inverter in a dq coordinate system, wherein the current state equation comprises a power grid voltage disturbance term, a variable coupling term and a model parameter deviation term;
the conversion unit is used for carrying out coordinate transformation on the acquired three-phase current to obtain d-axis and q-axis components of the three-phase current;
the self-reactive interference control unit is used for estimating the power grid voltage disturbance item, the variable coupling item and the model parameter deviation item as unknown disturbance, and calculating the control quantity of a d axis and a q axis by using the estimated value of the unknown disturbance; and performing active disturbance rejection control on the d-axis component and the q-axis component of the three-phase current according to the control quantity of the d-axis component and the control quantity of the q-axis component respectively.
8. The grid-connected inverter low-frequency harmonic current control device according to claim 7, further comprising a voltage reconstruction unit;
the voltage reconstruction unit is used for acquiring d-axis and q-axis components of the output voltage of the inverter by adopting a voltage reconstruction method.
9. The grid-connected inverter low-frequency harmonic current control device according to claim 8, wherein the self-reactive interference control unit includes:
the estimation module is used for constructing an extended state observer by using d-axis and q-axis components of the output voltage and d-axis and q-axis components of the three-phase current; estimating d-axis and q-axis components of the three-phase current and unknown disturbance by using the extended state observer to obtain respective corresponding estimated values;
the first calculation module is used for respectively obtaining the difference between a given d-axis current and the estimated value of the d-axis component and the difference between a given q-axis current and the estimated value of the q-axis component to obtain d-axis and q-axis current errors;
and the second calculation module is used for forming the control quantity of the d axis and the q axis by utilizing the linear feedback corresponding to the current errors of the d axis and the q axis and the compensation quantity corresponding to the estimation value of the unknown disturbance.
10. The grid-connected inverter low-frequency harmonic current control device according to claim 7 or 9, wherein the self-reactive interference control unit further comprises a modulation module;
the modulation module is used for converting the control quantity of the d axis and the q axis into the control quantity in a two-phase static coordinate system through inverse Park conversion, carrying out pulse width modulation on the converted control quantity to obtain a switching tube driving signal, and inputting the switching tube driving signal into an inverter to carry out active disturbance rejection control on the d axis and the q axis components of grid-connected current.
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