CN108390413B - Method for improving adaptability of distributed photovoltaic to alternating current-direct current hybrid micro-grid - Google Patents

Method for improving adaptability of distributed photovoltaic to alternating current-direct current hybrid micro-grid Download PDF

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CN108390413B
CN108390413B CN201810374149.4A CN201810374149A CN108390413B CN 108390413 B CN108390413 B CN 108390413B CN 201810374149 A CN201810374149 A CN 201810374149A CN 108390413 B CN108390413 B CN 108390413B
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transfer function
current
controller
coefficient
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CN108390413A (en
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李鹏
张新宗
王敏
刘嘉伟
余杰
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State Grid Zhejiang Electric Power Co Ltd
North China Electric Power University
Shaoxing Power Supply Co of State Grid Zhejiang Electric Power Co Ltd
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State Grid Zhejiang Electric Power Co Ltd
North China Electric Power University
Shaoxing Power Supply Co of State Grid Zhejiang Electric Power Co Ltd
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    • H02J3/383—
    • 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
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    • 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
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    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Abstract

A method for improving adaptability of a distributed photovoltaic grid to an alternating current-direct current hybrid micro-grid comprises the following steps: determining double closed-loop control parameters of the distributed photovoltaic grid-connected system under the condition of a strong power grid: proportional regulation coefficient of PI controller, integral regulation coefficient of PI controller and capacitance current feedback coefficient; virtual parallel impedance based on output impedance under weak grid conditions is realized; and determining parameters of a phase lag link after system compensation and the value range of the parallel inductor. The invention ensures that the system can stably run under the condition of a strong power grid and can meet the requirements of steady state and transient state; the adaptability of the system to weak power grids is improved. The method ensures the grid-connected performance of the system under the condition of strong power grid through the parameter setting of the double closed loops under the condition of strong power grid, and simultaneously improves the adaptability of the system to weak power grid by adopting a method of virtual parallel impedance post-lag link compensation and parallel inductance.

Description

Method for improving adaptability of distributed photovoltaic to alternating current-direct current hybrid micro-grid
Technical Field
The invention relates to a method for improving the adaptability of a micro-grid. In particular to a method for improving the adaptability of a distributed photovoltaic grid to an alternating current and direct current hybrid micro-grid.
Background
With the continuous advance of the industrial process in China, the exhaustion of energy and environmental pollution become main factors for inhibiting the progress of modern industry gradually, and new energy technologies represented by photovoltaic and fans gradually go into the visual field of people and occupy gradually rising proportions in the energy structure in China. The distributed photovoltaic self-generation self-use and local condition-based characteristics are rapidly developed in China. As a key interface of a distributed photovoltaic and alternating current-direct current hybrid micro-grid, the performance of a grid-connected inverter has a decisive influence on the grid-connected performance of the distributed photovoltaic.
In order to ensure high-quality grid connection of grid connection current of the distributed photovoltaic grid connection system, a grid connection inverter is generally incorporated into an alternating current-direct current hybrid micro-grid through an L-type or LCL-type filter. Under the effect of realizing the same filtering effect, the LCL type filter can obtain smaller volume and lower cost than the L type filter, so the LCL type filter has wider application in the grid-connected inverter. However, the third-order structure of the LCL type filter itself may bring a resonance peak to the distributed photovoltaic grid-connected system, thereby seriously affecting the stable operation of the grid-connected system. Therefore, in order to suppress the resonance peak of the LCL type filter and simultaneously realize direct and accurate control of the grid-connected current, the grid-connected inverter generally adopts a dual-current closed loop structure of a capacitance current inner loop and a grid-connected current outer loop. Meanwhile, in order to ensure that the grid-connected system has good steady-state and transient-state performance, current regulator parameters and capacitance current feedback coefficients need to be correspondingly set according to corresponding steady-state and transient-state performance indexes.
Along with the high-density access of distributed energy in the alternating current-direct current hybrid microgrid, the microgrid is more and more characterized by a weak power grid, the impedance of the power grid is increased, and meanwhile, background harmonics of the power grid are richer. Under the condition, the Total Harmonic Distortion (THD) and the Power Factor (PF) of the grid-connected current of the distributed photovoltaic grid-connected system, which originally operates well after being set under the condition of a strong power grid, may no longer meet the requirements of the related grid-connected standard.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for improving the adaptability of a distributed photovoltaic to an alternating current-direct current hybrid micro-grid, which can maintain the safe and stable operation of a system under the condition of a strong power grid and simultaneously enhance the adaptability of the system to a weak power grid.
The technical scheme adopted by the invention is as follows: a method for improving adaptability of a distributed photovoltaic grid to an alternating current-direct current hybrid micro-grid comprises the following steps:
1) determining double closed-loop control parameters of the distributed photovoltaic grid-connected system under the condition of a strong power grid: proportional regulation coefficient of PI controller, integral regulation coefficient of PI controller and capacitance current feedback coefficient;
2) virtual parallel impedance based on output impedance under weak grid conditions is realized;
3) determining the post-compensation phase lag element G of the systemhParameter of(s) and parallel inductance LPThe value range of (a).
The distributed photovoltaic grid-connected system double closed-loop control parameters under the condition of the strong power grid in the step 1) comprise:
transfer function G of grid-connected current controller formed by PI controlleri2(s)：
Gi2(s)＝KP+KI/s (1)
In the formula, KPFor proportional adjustment factor of PI controller, KIIs the integral regulating coefficient of the PI controller, and s is a Laplace operator;
according to transfer function G of grid-connected current controlleri2(s) obtaining an open-loop transfer function G of the single-phase networking system under the control of the double closed loops without adding a correction compensation deviceo(s)：
Figure GDA0002731413200000021
In the formula i2(s) and
Figure GDA0002731413200000022
respectively a grid-connected current transfer function and a grid-connected reference current transfer function, KPWMIs the proportional gain of the inverter, L1、L2And C is inverter side inductance of LCL filter, grid side inductance of LCL filter and LCL filter respectivelyFilter capacitance of wave filter HcIs a capacitance current feedback coefficient;
due to the open loop cut-off frequency omega of the systemc0Much higher than fundamental frequency omega0At this time, the LCL filter is approximated to have a total inductance of L1+L2The L-shaped filter simultaneously considers the grid-connected current controller as a pure proportional link, and the amplitude | G of the open-loop transfer function of the systemo(s) | is:
Figure GDA0002731413200000023
according to the system at the open loop cut-off frequency omegac0The amplitude of the open-loop transfer function is 1, and the proportional regulation coefficient K of the PI controller is obtainedP：
Figure GDA0002731413200000024
By the open loop transfer function G of the systemo(s) obtaining a system phase angle margin γ0：
Figure GDA0002731413200000025
In the formula, ωrIs the natural resonance angular frequency of the LCL filter
Figure GDA0002731413200000026
Simultaneously obtaining a system gain margin GM0：
GM0＝-20lg|Go(jωr)| (6)
Wherein, | Go(jωr) I is the system open loop transfer function Go(s) at the natural resonant angular frequency ω of the LCL filterrThe open loop transfer function amplitude of (d);
also, the open loop transfer function G of the systemo(s) obtaining a fundamental frequency ω0Transfer function of open loopGain Gω0：
Figure GDA0002731413200000027
Wherein j is an imaginary unit;
when the system phase angle margin gamma0Gain margin GM0And fundamental frequency omega0At open loop transfer function gain Gω0After determination, the capacitance current feedback coefficient H is obtainedcAnd integral adjustment coefficient K of PI controllerIThe value range of (a); first of all by a gain margin GM0Obtaining the feedback coefficient H of the capacitance currentcLower limit of value Hcl：
Figure GDA0002731413200000031
According to the required system phase angle margin gamma0And fundamental frequency omega0At open loop transfer function gain Gω0Obtaining the feedback coefficient H of the capacitance currentcUpper limit of value Hch：
Figure GDA0002731413200000032
By the feedback coefficient H of the capacitance currentcLower limit of value HclAnd upper value limit HchThe feedback coefficient H of the capacitance current meeting the requirement is obtainedc；
Then, the system fundamental frequency ω0At open loop transfer function gain Gω0Determining integral regulating coefficient K of PI controllerIValue lower limit K ofIl：
Figure GDA0002731413200000033
By the system phase angle margin gamma0And the determined proportional adjustment coefficient K of the PI controllerPAnd a capacitor current feedback systemNumber HcObtaining integral regulating coefficient K of PI controllerIUpper limit K of valueIh：
Figure GDA0002731413200000034
Thus, the coefficient K is adjusted by the integral of the PI controllerIValue lower limit K ofIlAnd upper value limit KIhThen the integral regulating coefficient K of the PI controller is obtainedI。
When the phase angle margin gamma of the system is not satisfied0Gain margin GM0And fundamental frequency omega0At open loop transfer function gain Gω0When the distributed photovoltaic grid-connected system double closed-loop control parameters are required under the condition of strong power grid, the system phase angle margin gamma is changed0Gain margin GM0And fundamental frequency omega0At open loop transfer function gain Gω0Until obtaining the double closed loop control parameter meeting the grid-connected performance.
The step 2) comprises the following steps:
obtaining grid-connected current transfer function i from distributed photovoltaic single-phase grid-connected system structure2(s) expression:
Figure GDA0002731413200000035
in the formula (I), the compound is shown in the specification,
Figure GDA0002731413200000036
for the transfer function of the grid-connected reference current uPCCFor the system point of common coupling voltage, i2s(s) and Z0(s) respectively an equivalent current source and an equivalent output impedance, K, of the distributed photovoltaic single-phase grid-connected system Noton equivalent circuitPWMIs the proportional gain of the inverter, L1、L2And C is inverter side inductance of LCL filter, grid side inductance of LCL filter and filter capacitance of LCL filter, HcAs a feedback coefficient of capacitance current, Gi2(s) transmission of grid-connected current controller composed of PI controllerA transfer function, s being a laplace operator;
system equivalent output impedance Z0The expression of(s) is:
Figure GDA0002731413200000041
virtual parallel impedance ZepThe specific expression of(s) is
Figure GDA0002731413200000042
Virtual parallel impedance Zep(s) can not be directly realized in a distributed photovoltaic single-phase grid-connected system structure, and the voltage u of a system common coupling point is requiredPCCFeedforward loop Gq(s) is added to the system by the system equivalent output impedance Z0(s) and a virtual parallel impedance Zep(s) obtaining a system pcc voltage uPCCFeedforward loop GqThe expression of(s) is:
Figure GDA0002731413200000043
in the formula, GdAnd(s) is a delay link of digital control.
The step 3) comprises the following steps:
in order to maintain the open loop cut-off frequency omega of the systemc0The gain of the system open loop transfer function of the following frequency band is unchanged, and the phase lag back link Gh(s) takes the form:
Figure GDA0002731413200000044
in the formula, tau is a time constant of a phase lag link; p is the absolute value of the pole of the hysteresis link, and p is 1/tau; s is a laplace operator;
the pole absolute value p of the hysteresis loop refers to the inherent resonance angular frequency omega of the LCL filterrThe values are as follows:
p＝(0.5～0.8)ωr (17)
thus, the time constant τ of the phase lag element can be set to a value in the range of
Figure GDA0002731413200000045
Under the condition of a weak power grid, the grid inductance L is consideredgResonance frequency omega of system under existence conditionrgComprises the following steps:
Figure GDA0002731413200000046
in the formula, L1、L2C is inverter side inductance of the LCL filter, grid side inductance of the LCL filter and filter capacitance of the LCL filter respectively;
equivalent grid inductance L of system after parallel connection of inductance at output end of grid-connected invertergdComprises the following steps:
Figure GDA0002731413200000047
the system is connected with an inductor L in parallel at the output end of the grid-connected inverterPRear resonant frequency omegargdIs composed of
Figure GDA0002731413200000048
With the inductance L of the networkgThe resonant frequency of the system tends to decrease, and in order to keep the system connected with the inductor L in parallel at the output end of the grid-connected inverterPRear resonant frequency omegargdWithout deviating from the natural resonant angular frequency omega of the LCL filterrParallel connection of an inductor LPRear resonant frequency omegargdHas a value range of
ωrgd＝aωr (22)
Wherein a is 0.9 to 0.95;
further, the parallel inductance L is obtainedPHas a value range of
Figure GDA0002731413200000051
According to the method for improving the adaptability of the distributed photovoltaic grid to the alternating current-direct current hybrid micro-grid, firstly, the current regulator parameters and the capacitance current feedback coefficients of the grid-connected system under the double closed-loop control are set under the condition of a strong power grid, so that the system can stably run under the condition of the strong power grid, and meanwhile, the requirements of a steady state and a transient state can be met; then establishing an output impedance model of the grid-connected system under the condition of a weak power grid, and correcting the output impedance of the system by adopting a virtual parallel impedance method; finally, aiming at the problem of harmonic oscillation brought by introducing a differential term into the process of realizing the parallel virtual impedance, a hysteresis link is added into an outer ring of the grid-connected current of the system, and an inductor is connected in parallel at the output end of the grid-connected inverter to improve the adaptability of the system to a weak power grid. The method ensures the grid-connected performance of the system under the condition of strong power grid through the parameter setting of the double closed loops under the condition of strong power grid, and simultaneously improves the adaptability of the system to weak power grid by adopting a method of virtual parallel impedance post-lag link compensation and parallel inductance.
Drawings
FIG. 1 is an overall flow chart of a method for improving the adaptability of a distributed photovoltaic to an AC/DC hybrid microgrid according to the invention;
FIG. 2 is a diagram of a distributed photovoltaic single-phase grid-connected system implementing the method of the present invention;
FIG. 3a shows grid-connected current i of the system after the double closed-loop parameters are determined under the condition of strong power grid2A waveform diagram;
FIG. 3b is a grid-connected current i after the system realizes the virtual parallel impedance under the condition of strong power grid2A waveform diagram;
FIG. 3c shows the phase lag compensation and shunt inductance L of the system under the condition of strong power gridPRear grid-connected current i2A waveform diagram;
FIG. 4a is system grid inductance L under weak grid conditionsgIs 0.6mH and realizes the grid-connected current i of the system after the virtual parallel impedance2A waveform diagram;
FIG. 4b is the system grid inductance L under weak grid conditionsgIs 1.3mH and realizes the grid-connected current i of the system after the virtual parallel impedance2A waveform diagram;
FIG. 5a is system grid inductance L under weak grid conditionsgSystem phase lag compensation and shunt inductance L at 0.6mHPRear grid-connected current i2A waveform diagram;
FIG. 5b is the system grid inductance L under weak grid conditionsgSystem phase lag compensation and shunt inductance L at 1.3mHPRear grid-connected current i2And (4) waveform diagrams.
Detailed Description
The following describes a method for improving adaptability of a distributed photovoltaic-ac/dc hybrid microgrid according to the present invention in detail with reference to the following embodiments and accompanying drawings.
According to the method for improving the adaptability of the distributed photovoltaic grid to the alternating current-direct current hybrid micro-grid, the grid-connected current quality of the system under the condition of a strong power grid can be ensured through setting of double closed-loop parameters of the distributed photovoltaic single-phase grid-connected system, and meanwhile, the adaptability of the system to a weak power grid is enhanced by adopting a method of parallel virtual impedance post-lag link compensation and parallel inductance.
As shown in fig. 1, the method for improving the adaptability of a distributed photovoltaic to an ac/dc hybrid microgrid comprises the following steps:
1) determining double closed-loop control parameters of the distributed photovoltaic grid-connected system under the condition of a strong power grid: proportional regulation coefficient of PI controller, integral regulation coefficient of PI controller and capacitance current feedback coefficient; the distributed photovoltaic grid-connected system double closed-loop control parameters under the condition of the strong power grid comprise:
transfer function G of grid-connected current controller formed by PI controlleri2(s)：
Gi2(s)＝KP+KI/s (1)
In the formula, KPFor PI controlProportional coefficient of regulation, K, of the deviceIIs the integral regulating coefficient of the PI controller, and s is a Laplace operator;
according to transfer function G of grid-connected current controlleri2(s) obtaining an open-loop transfer function G of the single-phase networking system under the control of the double closed loops without adding a correction compensation deviceo(s)：
Figure GDA0002731413200000061
In the formula i2(s) and
Figure GDA0002731413200000062
respectively a grid-connected current transfer function and a grid-connected reference current transfer function, KPWMIs the proportional gain of the inverter, L1、L2And C is inverter side inductance of LCL filter, grid side inductance of LCL filter and filter capacitance of LCL filter, HcIs a capacitance current feedback coefficient;
due to the open loop cut-off frequency omega of the systemc0Much higher than fundamental frequency omega0At this time, the LCL filter is approximated to have a total inductance of L1+L2The L-shaped filter simultaneously considers the grid-connected current controller as a pure proportional link, and the amplitude | G of the open-loop transfer function of the systemo(s) | is:
Figure GDA0002731413200000063
according to the system at the open loop cut-off frequency omegac0The amplitude of the open-loop transfer function is 1, and the proportional regulation coefficient K of the PI controller is obtainedP：
Figure GDA0002731413200000064
Thus, the cut-off frequency ω for the open loop by the systemc0To obtain the proportional regulation coefficient K of the PI controllerP；
By the open loop transfer function G of the systemo(s) obtaining a system phase angle margin γ0：
Figure GDA0002731413200000065
In the formula, ωrIs the natural resonance angular frequency of the LCL filter
Figure GDA0002731413200000066
Simultaneously obtaining a system gain margin GM0：
GM0＝-20lg|Go(jωr)| (6)
Wherein, | Go(jωr) I is the system open loop transfer function Go(s) at the natural resonant angular frequency ω of the LCL filterrThe open loop transfer function amplitude of (d);
also, the open loop transfer function G of the systemo(s) obtaining a fundamental frequency ω0At open loop transfer function gain Gω0：
Figure GDA0002731413200000071
Wherein j is an imaginary unit;
when the system phase angle margin gamma0Gain margin GM0And fundamental frequency omega0At open loop transfer function gain Gω0After determination, the capacitance current feedback coefficient H is obtainedcAnd integral adjustment coefficient K of PI controllerIThe value range of (a); first of all by a gain margin GM0Obtaining the feedback coefficient H of the capacitance currentcLower limit of value Hcl：
Figure GDA0002731413200000072
According to the required system phase angle margin gamma0And fundamental frequencyω0At open loop transfer function gain Gω0Obtaining the feedback coefficient H of the capacitance currentcUpper limit of value Hch：
Figure GDA0002731413200000073
By the feedback coefficient H of the capacitance currentcLower limit of value HclAnd upper value limit HchThe feedback coefficient H of the capacitance current meeting the requirement is obtainedc；
Then, the system fundamental frequency ω0At open loop transfer function gain Gω0Determining integral regulating coefficient K of PI controllerIValue lower limit K ofIl：
Figure GDA0002731413200000074
By the system phase angle margin gamma0And the determined proportional adjustment coefficient K of the PI controllerPAnd the feedback coefficient H of the capacitor currentcObtaining integral regulating coefficient K of PI controllerIUpper limit K of valueIh：
Figure GDA0002731413200000075
Thus, the coefficient K is adjusted by the integral of the PI controllerIValue lower limit K ofIlAnd upper value limit KIhThen the integral regulating coefficient K of the PI controller is obtainedI。
It should be noted that the system phase angle margin γ is not satisfied when0Gain margin GM0And fundamental frequency omega0At open loop transfer function gain Gω0When the distributed photovoltaic grid-connected system double closed-loop control parameters are required under the condition of strong power grid, the system phase angle margin gamma is changed0Gain margin GM0And fundamental frequency omega0At open loop transfer function gain Gω0Until a pair satisfying the grid-connection performance is obtainedA closed loop control parameter. That is, if the system determines the phase angle margin γ0Gain margin GM0And fundamental frequency omega0At open loop transfer function gain Gω0Indexes are too strict, distributed photovoltaic grid-connected system double closed loop control parameters under the condition of strong power grid which possibly cannot meet the requirements can not be obtained, and at the moment, the system phase angle margin gamma should be properly widened0Gain margin GM0And fundamental frequency omega0At open loop transfer function gain Gω0And (3) redesigning the double closed-loop control parameters of the system until the double closed-loop control parameters meeting the grid-connected performance are obtained.
2) Virtual parallel impedance based on output impedance under weak grid conditions is realized; the method comprises the following steps:
obtaining a grid-connected current transfer function i from the distributed photovoltaic single-phase grid-connected system structure shown in FIG. 22(s) expression:
Figure GDA0002731413200000081
in the formula (I), the compound is shown in the specification,
Figure GDA0002731413200000082
for the transfer function of the grid-connected reference current uPCCFor the system point of common coupling voltage, i2s(s) and Z0(s) respectively an equivalent current source and an equivalent output impedance, K, of the distributed photovoltaic single-phase grid-connected system Noton equivalent circuitPWMIs the proportional gain of the inverter, L1、L2And C is inverter side inductance of LCL filter, grid side inductance of LCL filter and filter capacitance of LCL filter, HcAs a feedback coefficient of capacitance current, Gi2(s) is a transfer function of a grid-connected current controller composed of PI controllers, and s is a Laplace operator;
system equivalent output impedance Z0The expression of(s) is:
Figure GDA0002731413200000083
in order to enhance the system to restrain the power grid background harmonic wave and the power grid impedance ZgRobustness of the(s) variations, the need to increase the system equivalent output impedance Z0(s) amplitude; theoretically, if the equivalent output impedance Z of the system is0(s) two ends are connected in parallel with an equivalent output impedance Z of the system0(s) impedances with equal amplitude and opposite phase can realize infinite gain of the amplitude of the equivalent output impedance of the system after the virtual impedance is connected in parallel, thus avoiding the impedance Z of the power gridgThe intersection of(s) improves the power grid background harmonic suppression capability of the system and the power grid impedance Zg(s) robustness of the variation;
virtual parallel impedance ZepThe specific expression of(s) is
Figure GDA0002731413200000084
Virtual parallel impedance Zep(s) can not be directly realized in a distributed photovoltaic single-phase grid-connected system structure, and the voltage u of a system common coupling point is requiredPCCFeedforward loop Gq(s) is added to the system by the system equivalent output impedance Z0(s) and a virtual parallel impedance Zep(s) obtaining a system pcc voltage uPCCFeedforward loop GqThe expression of(s) is:
Figure GDA0002731413200000085
in the formula, GdAnd(s) is a delay link of digital control.
3) Determining the post-compensation phase lag element G of the systemhParameter of(s) and parallel inductance LPThe value range of (a). The method comprises the following steps:
voltage u from system point of common couplingPCCFeedforward loop GqThe expression of(s) shows that although the amplitude of the equivalent output impedance of the system can be improved by the parallel virtual impedance, the introduced differential link can amplify the background harmonic of the power grid, and the background harmonic is weakUnder the condition of a power grid, the grid-connected current waveform quality of the system is more seriously distorted, so that a phase lag link G is added to the system at the outer ring of the grid-connected currenth(s) compensating the system;
in order to maintain the open loop cut-off frequency omega of the systemc0The gain of the system open loop transfer function of the following frequency band is unchanged, and the phase lag back link Gh(s) takes the form:
Figure GDA0002731413200000091
in the formula, τ is a time constant of the phase lag link, p is an absolute value of a pole of the phase lag link, and p is 1/τ; s is a laplace operator;
the pole absolute value p of the hysteresis loop refers to the inherent resonance angular frequency omega of the LCL filterrThe values are as follows:
p＝(0.5～0.8)ωr (17)
thus, the time constant τ of the phase lag element can be set to a value in the range of
Figure GDA0002731413200000092
According to the waveform quality requirement of the grid-connected current of the system, the time constant tau of the phase lag link can be obtained within the value range of the time constant tau of the phase lag link;
because the background harmonic wave of the power grid is mainly distributed at low frequency, in order to better improve the performance of the system, a phase lag link G is added to the systemh(s) simultaneously connecting an inductor L in parallel at the output end of the grid-connected inverterPThe resonant frequency of the system is moved to high frequency, so that the probability of harmonic oscillation of the system can be avoided;
under the condition of a weak power grid, the grid inductance L is consideredgResonance frequency omega of system under existence conditionrgComprises the following steps:
Figure GDA0002731413200000093
in the formula, L1、L2C is inverter side inductance of the LCL filter, grid side inductance of the LCL filter and filter capacitance of the LCL filter respectively;
equivalent grid inductance L of system after parallel connection of inductance at output end of grid-connected invertergdComprises the following steps:
Figure GDA0002731413200000094
the system is connected with an inductor L in parallel at the output end of the grid-connected inverterPRear resonant frequency omegargdIs composed of
Figure GDA0002731413200000095
With the inductance L of the networkgThe resonant frequency of the system tends to decrease, and in order to keep the system connected with the inductor L in parallel at the output end of the grid-connected inverterPRear resonant frequency omegargdWithout deviating from the natural resonant angular frequency omega of the LCL filterrParallel connection of an inductor LPRear resonant frequency omegargdHas a value range of
ωrgd＝aωr (22)
Wherein a is 0.9 to 0.95;
further, the parallel inductance L is obtainedPHas a value range of
Figure GDA0002731413200000101
From the parallel inductance LPThe value range of the inductor can obtain the proper parallel inductance L according to the grid-connected performance requirement of the systemP。
In order to verify the correctness and rationality of the method for improving the adaptability of the distributed photovoltaic to the alternating current-direct current hybrid micro-grid, the model shown in the figure 2 is built on an MATLAB/Simulink platform to perform simulation verification on the method. The system parameters are shown in table 1.
TABLE 1 System parameters
Figure GDA0002731413200000102
FIG. 3a, FIG. 3b and FIG. 3c are diagrams illustrating the system implementing the virtual parallel impedance and the phase lag compensation and parallel inductance L after determining the parameters of the double closed loops, under the condition of strong power gridPRear grid-connected current i2And (3) a waveform diagram, wherein the grid-connected current of the system after the double closed-loop parameters are determined has good waveform quality and completely meets the grid-connected requirement of the system. Meanwhile, as can be seen from fig. 3b and 3c, after the grid-connected system uses the method of the present invention, the grid-connected performance of the system under the condition of strong power grid is not affected.
FIG. 4a and FIG. 4b are system grid inductance L under weak grid conditiongWhen the current is 0.6mH and 1.3mH and the system grid-connected current i is obtained after the virtual parallel impedance is realized2The waveform diagram shows that after virtual parallel impedance is realized under weak grid conditions, because of the introduction of a differential link, background harmonic waves of a power grid are amplified to a certain degree, and therefore obvious harmonic oscillation phenomenon occurs to grid-connected current of a system.
FIG. 5a and FIG. 5b are system grid inductance L under weak grid conditiongThe system phase lag compensation and parallel inductance L is 0.6mH and 1.3mHPRear grid-connected current i2Waveform, as can be seen from the figure, the system phase lag compensation and parallel inductance LPThe harmonic oscillation phenomenon of the rear grid-connected current is well inhibited, and the waveform quality of the grid-connected current is obviously improved. On the other hand, the rationality and the effectiveness of the method for improving the adaptability of the distributed photovoltaic to the alternating current and direct current hybrid micro-grid are verified.

Claims (4)

1. A method for improving adaptability of a distributed photovoltaic grid to an alternating current-direct current hybrid micro-grid is characterized by comprising the following steps:
1) determining double closed-loop control parameters of the distributed photovoltaic grid-connected system under the condition of a strong power grid: proportional regulation coefficient of PI controller, integral regulation coefficient of PI controller and capacitance current feedback coefficient;
2) virtual parallel impedance based on output impedance under weak grid conditions is realized; the method comprises the following steps:
obtaining grid-connected current transfer function i from distributed photovoltaic single-phase grid-connected system structure2(s) expression:
Figure FDA0002731413190000011
in the formula (I), the compound is shown in the specification,
Figure FDA0002731413190000012
for the transfer function of the grid-connected reference current uPCCFor the system point of common coupling voltage, i2s(s) and Z0(s) respectively an equivalent current source and an equivalent output impedance, K, of the distributed photovoltaic single-phase grid-connected system Noton equivalent circuitPWMIs the proportional gain of the inverter, L1、L2And C is inverter side inductance of LCL filter, grid side inductance of LCL filter and filter capacitance of LCL filter, HcAs a feedback coefficient of capacitance current, Gi2(s) is a transfer function of a grid-connected current controller composed of PI controllers, and s is a Laplace operator;
system equivalent output impedance Z0The expression of(s) is:
Figure FDA0002731413190000013
virtual parallel impedance ZepThe specific expression of(s) is
Figure FDA0002731413190000014
Virtual parallel impedance Zep(s) andcan not be directly realized in a distributed photovoltaic single-phase grid-connected system structure, and needs to use the voltage u of a system common coupling pointPCCFeedforward loop Gq(s) is added to the system by the system equivalent output impedance Z0(s) and a virtual parallel impedance Zep(s) obtaining a system pcc voltage uPCCFeedforward loop GqThe expression of(s) is:
Figure FDA0002731413190000015
in the formula, Gd(s) is a delay link of digital control;
3) determining the post-compensation phase lag element G of the systemhParameter of(s) and parallel inductance LPThe value range of (a).
2. The method for improving the adaptability of the distributed photovoltaic grid to the alternating current-direct current hybrid microgrid according to claim 1, characterized in that the double closed-loop control parameters of the distributed photovoltaic grid-connected system under the condition of the high power grid in the step 1) comprise:
transfer function G of grid-connected current controller formed by PI controlleri2(s)：
Gi2(s)＝KP+KI/s (1)
In the formula, KPFor proportional adjustment factor of PI controller, KIIs the integral regulating coefficient of the PI controller, and s is a Laplace operator;
according to transfer function G of grid-connected current controlleri2(s) obtaining an open-loop transfer function G of the single-phase networking system under the control of the double closed loops without adding a correction compensation deviceo(s)：
Figure FDA0002731413190000021
In the formula i2(s) and
Figure FDA0002731413190000022
respectively a grid-connected current transfer function and a grid-connected reference current transfer function, KPWMIs the proportional gain of the inverter, L1、L2And C is inverter side inductance of LCL filter, grid side inductance of LCL filter and filter capacitance of LCL filter, HcIs a capacitance current feedback coefficient;
due to the open loop cut-off frequency omega of the systemc0Much higher than fundamental frequency omega0At this time, the LCL filter is approximated to have a total inductance of L1+L2The L-shaped filter simultaneously considers the grid-connected current controller as a pure proportional link, and the amplitude | G of the open-loop transfer function of the systemo(s) | is:
Figure FDA0002731413190000023
according to the system at the open loop cut-off frequency omegac0The amplitude of the open-loop transfer function is 1, and the proportional regulation coefficient K of the PI controller is obtainedP：
Figure FDA0002731413190000024
By the open loop transfer function G of the systemo(s) obtaining a system phase angle margin γ0：
Figure FDA0002731413190000025
In the formula, ωrIs the natural resonance angular frequency of the LCL filter
Figure FDA0002731413190000026
Simultaneously obtaining a system gain margin GM0：
GM0＝-20lg|Go(jωr)| (6)
Wherein, | Go(jωr) I is the system open loop transfer function Go(s) at the natural resonant angular frequency ω of the LCL filterrThe open loop transfer function amplitude of (d);
also, the open loop transfer function G of the systemo(s) obtaining a fundamental frequency ω0At open loop transfer function gain Gω0：
Figure FDA0002731413190000027
Wherein j is an imaginary unit;
when the system phase angle margin gamma0Gain margin GM0And fundamental frequency omega0At open loop transfer function gain Gω0After determination, the capacitance current feedback coefficient H is obtainedcAnd integral adjustment coefficient K of PI controllerIThe value range of (a); first of all by a gain margin GM0Obtaining the feedback coefficient H of the capacitance currentcLower limit of value Hcl：
Figure FDA0002731413190000031
According to the required system phase angle margin gamma0And fundamental frequency omega0At open loop transfer function gain Gω0Obtaining the feedback coefficient H of the capacitance currentcUpper limit of value Hch：
Figure FDA0002731413190000032
By the feedback coefficient H of the capacitance currentcLower limit of value HclAnd upper value limit HchThe feedback coefficient H of the capacitance current meeting the requirement is obtainedc；
Then, the system fundamental frequency ω0At open loop transfer function gain Gω0Determining integral regulating coefficient K of PI controllerIValue lower limit K ofIl：
Figure FDA0002731413190000033
By the system phase angle margin gamma0And the determined proportional adjustment coefficient K of the PI controllerPAnd the feedback coefficient H of the capacitor currentcObtaining integral regulating coefficient K of PI controllerIUpper limit K of valueIh：
Figure FDA0002731413190000034
Thus, the coefficient K is adjusted by the integral of the PI controllerIValue lower limit K ofIlAnd upper value limit KIhThen the integral regulating coefficient K of the PI controller is obtainedI。
3. The method for improving adaptability of distributed photovoltaic to alternating current and direct current hybrid micro-grid according to claim 2, wherein when the system phase angle margin γ is not satisfied, the method is characterized in that0Gain margin GM0And fundamental frequency omega0At open loop transfer function gain Gω0When the distributed photovoltaic grid-connected system double closed-loop control parameters are required under the condition of strong power grid, the system phase angle margin gamma is changed0Gain margin GM0And fundamental frequency omega0At open loop transfer function gain Gω0Until obtaining the double closed loop control parameter meeting the grid-connected performance.
4. The method for improving the adaptability of the distributed photovoltaic AC/DC hybrid micro-grid according to claim 1, wherein the step 3) comprises the following steps:
in order to maintain the open loop cut-off frequency omega of the systemc0The gain of the system open loop transfer function of the following frequency band is unchanged, and the phase lag back link Gh(s) takes the form:
Figure FDA0002731413190000035
in the formula, tau is a time constant of a phase lag link; p is the absolute value of the pole of the hysteresis link, and p is 1/tau; s is a laplace operator;
the pole absolute value p of the hysteresis loop refers to the inherent resonance angular frequency omega of the LCL filterrThe values are as follows:
p＝(0.5～0.8)ωr (17)
thus, the time constant τ of the phase lag element can be set to a value in the range of
Figure FDA0002731413190000041
Under the condition of a weak power grid, the grid inductance L is consideredgResonance frequency omega of system under existence conditionrgComprises the following steps:
Figure FDA0002731413190000042
in the formula, L1、L2C is inverter side inductance of the LCL filter, grid side inductance of the LCL filter and filter capacitance of the LCL filter respectively;
equivalent grid inductance L of system after parallel connection of inductance at output end of grid-connected invertergdComprises the following steps:
Figure FDA0002731413190000043
the system is connected with an inductor L in parallel at the output end of the grid-connected inverterPRear resonant frequency omegargdIs composed of
Figure FDA0002731413190000044
With the inductance L of the networkgIncrease of (2)The resonant frequency of the system tends to decrease, and in order to keep the system connected with the inductor L in parallel at the output end of the grid-connected inverterPRear resonant frequency omegargdWithout deviating from the natural resonant angular frequency omega of the LCL filterrParallel connection of an inductor LPRear resonant frequency omegargdHas a value range of
ωrgd＝aωr (22)
Wherein a is 0.9 to 0.95;
further, the parallel inductance L is obtainedPHas a value range of
Figure FDA0002731413190000045
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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102163843A (en) * 2010-02-19 2011-08-24 Abb研究有限公司 Control method for single-phase grid-connected LCL inverter
CN103812135A (en) * 2014-03-10 2014-05-21 南京航空航天大学 Control method for improving adaptability of LCL type grid-connected inverter for weak grid
CN105305471A (en) * 2015-11-27 2016-02-03 广东电网有限责任公司电力科学研究院 Power distribution network flexible earthing device control system and parameter design method thereof
EP3079217A1 (en) * 2015-04-09 2016-10-12 ABB Technology AG Method for detecting islanding in grid connected power generation systems and related dc/ac converter apparatus
CN106877401A (en) * 2017-04-17 2017-06-20 华北电力大学（保定） Self adaptation improves LCL type grid-connected inverter system stability approach under weak grid conditions
CN107887910A (en) * 2017-12-13 2018-04-06 华北电力大学（保定） A kind of lead-lag compensation method for improving the grid-connected performance of distributed photovoltaic

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102163843A (en) * 2010-02-19 2011-08-24 Abb研究有限公司 Control method for single-phase grid-connected LCL inverter
CN103812135A (en) * 2014-03-10 2014-05-21 南京航空航天大学 Control method for improving adaptability of LCL type grid-connected inverter for weak grid
EP3079217A1 (en) * 2015-04-09 2016-10-12 ABB Technology AG Method for detecting islanding in grid connected power generation systems and related dc/ac converter apparatus
CN105305471A (en) * 2015-11-27 2016-02-03 广东电网有限责任公司电力科学研究院 Power distribution network flexible earthing device control system and parameter design method thereof
CN106877401A (en) * 2017-04-17 2017-06-20 华北电力大学（保定） Self adaptation improves LCL type grid-connected inverter system stability approach under weak grid conditions
CN107887910A (en) * 2017-12-13 2018-04-06 华北电力大学（保定） A kind of lead-lag compensation method for improving the grid-connected performance of distributed photovoltaic

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
并联逆变器集群无功控制之间的交互影响;夏曼 等;《电网与清洁能源》;20170430;第33卷(第4期);第92-98页 *

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