CN108879775A - A kind of unbalanced power supply photovoltaic DC-to-AC converter control method for coordinating considering current limit - Google Patents
A kind of unbalanced power supply photovoltaic DC-to-AC converter control method for coordinating considering current limit Download PDFInfo
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- H—ELECTRICITY
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
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- 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
- Y02E40/30—Reactive power compensation
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Abstract
The invention discloses a kind of unbalanced power supply photovoltaic DC-to-AC converter control method for coordinating for considering current limit, the separation scheme of the positive-negative sequence current based on trapper is analyzed first, then the inverter output power under unbalanced power grid has been quantified, the amount for influencing the active output of photovoltaic, idle output and current harmonics is weighted to obtain control amount k and γ, finally with active fluctuation and the minimum optimization aim of reactive power fluctuation, k and γ are optimized using Current harmonic distortion rate and output current limit as constraint condition.When the present invention makes power grid that imbalance fault occur, in the case where guaranteeing that current quality is qualified, electric current is not out-of-limit, keeps active and reactive power fluctuation minimum, improve the stability and reliability of control system.
Description
Technical field
The present invention relates to electric information fields, and in particular to a kind of unbalanced power supply photovoltaic DC-to-AC converter for considering current limit
Control method for coordinating.
Background technique
One of most common failure in electric system, the access of great power single phase load, single-phase load when unbalanced power supply
The factors such as the randomness of unbalanced distribution and single-phase load electricity consumption in three-phase system can all cause power grid three-phase voltage uneven
Weighing apparatus, sun shares the same light, and gird-connected inverter control strategy summary [J] electrotechnics journal in the case of magnificent unbalanced power supply is defended in osmanthus, and 2015,
30(14):241-246.When power grid imbalance of three-phase voltage, negative sequence component can be generated in network voltage, at this time due to based on flat
The photovoltaic DC-to-AC converter control strategy of weighing apparatus power grid lacks the control to negative sequence voltage, it will causes photovoltaic DC-to-AC converter big to power grid injection
The harmonic wave of amount, and the secondary pulsation of active power and reactive power can be generated.Therefore, photovoltaic inversion when unbalanced power supply is studied
Device control strategy is of great significance.
The principal contradiction of unbalanced power supply photovoltaic DC-to-AC converter control strategy is power swing and current harmonics size.With regard to one
For a three-phase system, generally there are two coordinate systems, i.e. the dq coordinate system of the static α β coordinate system of two-phase and two rotations.
Some have researched and proposed a kind of no phase-locked loop control strategy based on static α β coordinate system, first to inverse in the case of unbalanced power supply
Become device output to be quantified, obtains influencing the control amount of power swing and current harmonics by Clarke transform, utilize weighting
Thought realizes the coordinated control of photovoltaic DC-to-AC converter output power/current quality, Zhao Xin, golden new people, Zhou Fei, and is waited to be based on ratio
Integral-depression of order resonant regulator gird-connected inverter unbalance control [J] Proceedings of the CSEE, 2013,33 (19):84-
92.Some researchs are then based on two rotation dq coordinate systems, analyze the fluctuation of influence inverter active, nothing in the case of unbalanced power supply
The factor of function fluctuation and current quality obtains two coefficients by weighting, recycles neuron network PI controller controller, realize inversion
The multi-objective coordinated control of device, sun are shared the same light, and the multi-objective coordinated control strategy of gird-connected inverter in the case of magnificent unbalanced power supply is defended in osmanthus
Study [J] electrotechnics journal, 2015,30 (11):148-157.Also some have researched and proposed a kind of limitation imbalance fault hair
The method of inverter current, this method have multiplied the ratio of a rated current and maximum current, last light to reference current when raw
The output of volt inverter has obtained limitation Liu W Z, Guo X Q, Sulligoi G, et al.Enhanced power
quality and minimized peak current control in an inverter based microgrid
under unbalanced grid faults[C]//Energy Conversion Congress and
Exposition.IEEE,2016:1-6。
The studies above is focused primarily upon to current limliting problem during the coordinated control of unbalanced power grid inverter and imbalance fault
The improvement of method, it is rare while the case where consider coordinated control and current limit, only consider to will appear during coordinated control failure
The out-of-limit situation of electric current causes photovoltaic off-grid, only considers that the case where out-of-limit problem of electric current then will appear photovoltaic output drop influences system
The stability of system.
Summary of the invention
Improvement for defect existing for existing method or needs, the present invention propose a kind of imbalance for considering current limit
Electric current is out-of-limit during power grid photovoltaic DC-to-AC converter control method for coordinating solves coordinated control and only considers the out-of-limit control strategy of electric current
The problem of photovoltaic output drop, with active fluctuation and the minimum optimization aim of reactive power fluctuation, with Current harmonic distortion rate and defeated
Current limit is constraint condition out, and photovoltaic DC-to-AC converter is enable to provide effective control plan in real time when imbalance fault occurs for power grid
Slightly, in the case where guaranteeing that current quality is qualified, electric current is not out-of-limit, seek optimal solution, keep active and reactive power fluctuation minimum.
The present invention is achieved through the following technical solutions：
A kind of unbalanced power supply photovoltaic DC-to-AC converter control method for coordinating considering current limit, this method includes following step
Suddenly：
Step 1: the three-phase voltage of acquisition power grid and three-phase current and being coordinately transformed respectively to it, using trapper
The positive and negative order components of voltage and current after coordinate transform are extracted；
Step 2: quantization unbalanced power grid under inverter output power, to influence photovoltaic it is active output, it is idle output and
The amount of current harmonics is weighted to obtain the weight coefficient k and γ of coordinated control；
Step 3: with active power fluctuation and the minimum optimization aim of reactive power fluctuation, with Current harmonic distortion rate and
Output current limit is that constraint condition optimizes weight coefficient k and γ, building control optimization module；
Step 4: weight coefficient k and the γ optimal value of coordinated control is obtained by the control optimization module of above-mentioned building, it is right
Unbalanced power supply photovoltaic DC-to-AC converter carries out coordinated control.
Preferably, it is specifically included in the step 1：
The three-phase voltage and three-phase current of acquisition power grid simultaneously carry out dq coordinate transform to it respectively；Using trapper to through sitting
The positive and negative order components for marking transformed voltage and current extract to obtain：Positive sequence of the three-phase voltage under dq rotating coordinate system point
AmountAnd negative sequence componentPositive-sequence component of the three-phase current under dq rotating coordinate systemAnd negative sequence component
Wherein, Ed +、Eq +、Ed -、Eq -Respectively positive-sequence component amplitude and negative sequence component width of the three-phase voltage in d axis and q axis
Value；Id +、Iq +、Id -、Iq -Respectively positive-sequence component amplitude and negative sequence component amplitude of the three-phase current in d axis and q axis.
Preferably, in the step 2, quantify the inverter output power under unbalanced power grid, quantify under unbalanced power grid
Inverter output power, be embodied as：
When only considering fundamental wave, the network voltage of power grid three-phase imbalance ignores zero-sequence component, then orthogonal with following formula
Positive-negative sequence representation in components：
The instantaneous active power of inverter grid side is obtained by above-mentioned two formula and the expression formula of reactive power is：
P (t)=P0+Pc2cos(2ωt)+Ps2sin(2ωt)
Q (t)=Q0+Qc2cos(2ωt)+Qs2sin(2ωt)
In formula, P0、Q0Respectively active and idle average value；Pc2、Qc2Respectively secondary active and idle cosine value；
Ps2、Qs2Respectively secondary active and idle sine value；P0、Q0、Pc2、Qc2、Ps2、Qs2Expression formula it is as follows：
It is obtained by above formula, when unbalanced power supply, the output power of inverter also contains second harmonic in addition to fundametal compoment
Component and harmonic component；P0、Q0、Pc2、Qc2、Ps2、Qs2Pass through Id +、Id -、Iq +、Iq -The positive and negative order components control of four electric currents.
Preferably, by being weighted to obtain the reference vector expression formula of electric current to control target in 3 in the step 2
For：
In formula, 0≤k≤1,0≤γ≤1；Different control targets is realized by the change to weight coefficient k and γ.
Preferably, weight parameter k and γ are optimized in the step 3 and control optimization is specifically established using interior point method
Module：Use the active power fluctuation exported using photovoltaic DC-to-AC converter and reactive power fluctuation as optimization object function, expression formula
It is as follows：
min∑μΔP+λΔQ
In formula, Δ P and Δ Q are respectively the undulating value of active power and reactive power, μ and λ be respectively be Δ P and Δ Q
Weight；
Above-mentioned bound for objective function includes：
A. total harmonic distortion factor：ITHD≤ 5%
In formula, ITHDFor total harmonic distortion factor, its calculation formula is
In formula, I1For the fundametal compoment of electric current, InFor each harmonic component；Total harmonic distortion factor is no more than 5%；
B. current limit constrains：Idq≤Idq max
In formula, IdqFor three-phase transient current IabcTransient current under the dq coordinate system converted through Park, Idq maxFor
Gird-connected inverter maximum current limit value transforms to be worth under dq coordinate system.
The present invention has the advantage that and beneficial effect：
The present invention is optimal for optimization aim with active power fluctuation and reactive power fluctuation, with Current harmonic distortion rate and defeated
Current limit is constraint condition out, makes photovoltaic DC-to-AC converter when imbalance fault occurs for power grid, and guarantees that current quality is qualified, electric
In the case that stream does not get over line, active power and reactive power fluctuation can be made minimum；The present invention can effectively realize power grid not
The grid-connected current control of photovoltaic DC-to-AC converter when balance, and the dynamic property controlled is good.
Detailed description of the invention
Attached drawing described herein is used to provide to further understand the embodiment of the present invention, constitutes one of the application
Point, do not constitute the restriction to the embodiment of the present invention.In the accompanying drawings：
Fig. 1 is positive-negative sequence component extraction schematic diagram of the invention.
Fig. 2 is the circuit diagram of voltage-type three-phase grid-connected inverter of the invention.
Fig. 3 is the unbalanced power supply photovoltaic DC-to-AC converter coordinated control block diagram of consideration current limit of the invention.
Fig. 4 is the grid-connected simulation model of the invention using unbalanced power supply control strategy.
Fig. 5 is the simulation result using fixed k and γ of the invention.
Fig. 6 is the optimized flow chart of the invention to k and γ.
Fig. 7 is the simulation result of the k and γ using optimization of the invention.
Specific embodiment
To make the objectives, technical solutions, and advantages of the present invention clearer, below with reference to embodiment and attached drawing, to this
Invention is described in further detail, and exemplary embodiment of the invention and its explanation for explaining only the invention, are not made
For limitation of the invention.
Embodiment 1
In the present embodiment, it is a kind of consider current limit unbalanced power supply photovoltaic DC-to-AC converter control method for coordinating include following
Step：
1) when unbalanced power supply positive-negative sequence current voltage extraction scheme
The positive-negative sequence component extraction of voltage is to realize the premise of unbalanced power supply inverter control, positive-negative sequence component extraction
Precision directly influences the performance of control system.Currently, there are many kinds of the methods of positive-negative sequence component extraction, such as just based on decoupling
Negative phase-sequence extractive technique is based on quadrature component positive-negative sequence extractive technique and based on filtering positive-negative sequence extractive technique etc..In view of preceding two
The calculation amount of kind method is larger, will affect the efficiency of control, and the present invention uses the positive-negative sequence extracting method based on filter.Base
Generally there are low-pass filter and two kinds of trapper in the filter that the positive-negative sequence extractive technique of filter uses, low-pass filter can
To filter out higher hamonic wave, but the rapidity of system can be reduced；Although trapper can only filter out specific harmonic wave, its dynamic
Characteristic is better than low-pass filter, and the second harmonic of the mainly active power and reactive power generated when unbalanced power supply,
His harmonic component is less, can satisfy control system using trapper filtering progress positive-negative sequence component extraction and wants to reference current
It asks, therefore the present embodiment carries out the extraction of positive and negative order components using trapper, as shown in Figure 1, first by the three-phase electricity of unbalanced power grid
Press ea、eb、ecIt is converted by Park, transforms to voltage e under dq coordinate systemd、eq, ed、eqWaveform main component be fundamental wave and
Second harmonic；Then second harmonic, the remaining positive-sequence component e for being are filtered using trapperd +、eq +, finally again with subtracting just
Order components have just obtained the negative sequence component e under dq coordinate systemd -、eq -。
Trapper is a kind of special filter, its main feature is that the signal of specific frequency can be filtered and not to other signals
It works.Its transmission function is：
In formula, ω0Angular frequency for the signal for needing to filter out；K=1/Q, Q are the quality factors of filter.The frequency of power grid
Rate is f=50Hz, then ω0=2 π f=100 π.
2) inverter mathematical model when unbalanced power supply
As shown in Fig. 2, ea、eb、ecIt is power grid three-phase voltage, ia、ib、icIt is the three-phase current for injecting power grid, UdcIt is direct current
The voltage of side, C are the capacitors of DC side.Then when only considering fundamental wave, power grid potential when power grid three-phase imbalance is as follows：
In formula, Em +、Em -Respectively positive sequence voltage amplitude and negative sequence voltage amplitude；ω is mains frequency；θ+、θ-It is positive respectively
Sequence voltage initial phase angle and the initial phase angle of negative sequence voltage.Formula (2) has ignored zero-sequence component, can use orthogonal positive-negative sequence subscale
Show
In formula,
Its available voltage equation is
In formula, UdqsAnd IdqsRespectively contravarianter voltage and line current can be expressed as
Network voltage positive-negative sequence can be decoupled by bringing formula (3) into formula (7), and expression formula is as follows：
In formula, Udq +、Udq -Respectively three-phase voltage Ua、Ub、UcPositive-sequence component and negative phase-sequence point under dq rotating coordinate system
Amount.
When unbalanced power supply, the power of inverter grid side can be expressed as
In formula,Respectively positive-sequence component and negative sequence component of the three-phase current under dq rotating coordinate system, and
Formula (3) is brought into formula (12), the instantaneous active power of the available grid side of inverter at this time and reactive power
Expression formula is
P (t)=P0+Pc2cos(2ωt)+Ps2sin(2ωt) (13)
Q (t)=Q0+Qc2cos(2ωt)+Qs2sin(2ωt) (14)
In formula, P0、Q0Respectively active and idle average value；Pc2、Qc2Respectively secondary active and idle cosine value；
Ps2、Qs2Respectively secondary active and idle sine value.P0、Q0、Pc2、Qc2、Ps2、Qs2Expression formula it is as follows：
By formula (13)~(20) as can be seen that the output power of inverter is gone back in addition to fundametal compoment when unbalanced power supply
Contain second harmonic component and harmonic component.P0、Q0、Pc2、Qc2、Ps2、Qs2I can be passed throughd +、Id -、Iq +、Iq -Four reference currents
Control, but single control strategy cannot achieve the control to all targets.
3) reference current calculates
Formula (15)~(20) have calculated the reference current in the case of unbalanced power supply, by selecting different control mesh
Mark, can calculate corresponding current phasor.
(1) target 1 is controlled：Negative-sequence current is zero, inhibits current harmonics, keeps the current waveform of gird-connected inverter sinusoidal,
That is I-=0.Simultaneous (15)~(18) can obtain
The reference vector of forward-order current can be calculated by formula (21)
(2) target 2 is controlled：It keeps active power of output constant, inhibits the secondary pulsation of active power, i.e. Ps2=Pc2=
0.The reference vector of electric current can be obtained in joint type (15)~(18)
(3) target 3 is controlled：It keeps output reactive power constant, inhibits the secondary pulsation of reactive power, i.e. Qs2=Qc2=
0.The reference vector of electric current can be obtained in joint type (15), (18)~(20)
In formula,
It is all single control target that formula (22)~formula (24) is described, is not examined while realizing single control target
Consider the effect of remaining two kinds of control target, it is therefore desirable to the coordinated control of 3 kinds of control targets is realized by way of weighting.In conjunction with
Formula (22)~formula (24), the reference vector uniform expression for being weighted to obtain electric current to 3 kinds of control targets are
In formula, 0≤k≤1,0≤γ≤1.It can analyze out from formula (25), be by the change to weighting coefficient k and γ
Three kinds of different control targets can be achieved.As k=γ=1, control target 1 is realized；As k=γ=0, control target is realized
2；As k=1, γ=0, control target 3 is realized.In addition, can also be smoothly switched between zero and one by formula k and γ,
Realize the coordinated control of 3 kinds of targets.
4) consider the coordinated control mathematical model of current limit
Using formula (25) although the coordinated control of photovoltaic DC-to-AC converter output power may be implemented, imbalance fault is one
Dynamic process will appear the out-of-limit situation of electric current in the moment that failure generates, if current value is excessive will to will lead to photovoltaic plant
Off-grid influences the stability of system.Set forth herein using using current limliting limit value as constraint condition, optimized using interior point method,
The mathematical model of Controlling model is as follows：
(1) objective function
The active power fluctuation exported using photovoltaic DC-to-AC converter and reactive power fluctuation of this paper is optimization aim, mathematical table
It is as follows up to formula：
min∑μΔP+λΔQ (26)
In formula, Δ P and Δ Q are respectively the undulating value of active power and reactive power, μ and λ be respectively be Δ P and Δ Q
Weight.
(2) constraint condition
A. total harmonic distortion factor：ITHD≤ 5%
In formula, ITHDFor total harmonic distortion factor, its calculation formula is
In formula, I1For the fundametal compoment of electric current, InFor each harmonic component.In addition, according to country to grid-connected electric current matter
The requirement of amount, total harmonic distortion factor is no more than 5%.
B. current limit constrains：Idq≤Idq max
In formula, IdqFor three-phase transient current IabcTransient current under the dq coordinate system converted through Park, Idq maxFor
Gird-connected inverter maximum current limit value transforms to be worth under dq coordinate system.
C. optimized variable constrains：0≤k≤1,0≤γ≤1
In formula, k and γ are the weight of coordinated control and the optimized variable of this secondary control.
The unbalanced power supply photovoltaic DC-to-AC converter coordinated control block diagram of consideration current limit as shown in Figure 3, takes power grid first
Three-phase voltage and three-phase current be coordinately transformed；Then positive and negative order components are extracted according to the trapper in formula (1),
At the same time " Optimization Solution module " using obtain data perfect (26), the power calculation in formula (27), THD calculate, k and
The functions such as γ optimization；Reference current is calculated then according to formula (25)；And the reference current being calculated and reality are surveyed
The electric current measured relatively obtains control parameter, and the control signal for being finally coordinately transformed to obtain inverter completes control.
Embodiment 2
The unbalanced power supply photovoltaic DC-to-AC converter of the present embodiment considerations current limit based on the above embodiment is coordinated to control
Method processed, the grid-connected model for having built unbalanced power supply control method carries out emulation testing, in the model " unbalance "
Module is the inverter coordinating control module built after encapsulation according to Fig. 3, and the input of the module is mains voltage signal, inversion
The reference power signal of device current signal and photovoltaic cell.
Trapper positive-negative sequence separation principle in the present embodiment is obtained by formula (1), and trapper can be by specific frequency
The separation of positive-negative sequence is realized in the filtering of rate waveform, provides the data of needs for subsequent schedule implementation.
As shown in Fig. 2, when can analyze unbalanced power supply from figure inverter characteristics of output power.According to the ginseng in figure
Number, when only considering fundamental wave, shown in the power grid potential such as formula (2) when power grid three-phase imbalance.Ignore the zero sequence in formula (2)
Component can obtain formula (3) with orthogonal positive-negative sequence representation in components, and then obtain voltage equation (7)；Formula (3) is brought into
Formula (7) can decouple power grid electromotive force positive-negative sequence to obtain formula (10) and formula (11), and integrated (10) and formula (11) obtain formula
(12)；Formula (3) is brought into formula (12), the instantaneous active power of the available grid side of inverter at this time and the expression of reactive power
Formula formula (13)~formula (20), the output power of inverter removes base when from formula (13)~formula (20) as can be seen that when unbalanced power supply
Also contain second harmonic component and harmonic component outside wave component.P0、Q0、Pc2、Qc2、Ps2、Qs2I can be passed throughd +、Id -、Iq +、Iq -Four
A reference current control, but single control strategy cannot achieve the control to all targets.It is main that there are three control target：Control
Target 1 processed, negative-sequence current zero inhibit current harmonics, keep the current waveform of gird-connected inverter sinusoidal, i.e. I-=0, joint type
(15) the reference vector formula (22) of electric current can be obtained in~(18)；Target 2 is controlled, keeps active power of output constant, is inhibited active
The secondary pulsation of power, i.e. Ps2=Pc2=0, the reference vector formula (23) of electric current can be obtained in joint type (15)~formula (18)；Control
Target 3 keeps output reactive power constant, inhibits the secondary pulsation of reactive power, i.e. Qs2=Qc2=0, joint type (15), formula
(18) reference vector (24) of electric current can be obtained in~formula (20).Convolution (22)~formula (24) is weighted 3 kinds of control targets
Obtain the reference vector uniform expression (25) of electric current.The coordination of each target can be realized in transformation by k and γ 0 to 1
Control；It is control target 1 as k=γ=1；It is control target 2 as k=γ=0；It is control target as k=1, γ=0
3。
As shown in figure 3, being the block diagram of coordinated control, the overall process of entire control strategy is illustrated.Wherein " Optimization Solution "
Module is integrated with the Optimal Control Strategy of interior point method, and objective function is constraint shown in the fluctuation minimum such as formula (26) of active reactive
Condition is total harmonic distortion factor ITHDNot less than the instantaneous inverter current I under 5%, dq coordinate systemdqNo more than high current limit value
Idq max, control variable k and γ between 0 to 1.Trapper module is separated for positive-negative sequence.In addition, also with good grounds formula (25) is taken
The calculating reference current built, and the electric current that is obtained by comparing actual test and obtained by the reference current that formula (25) optimization calculates
To the module of control parameter, control parameter is converted to control signal by coordinate and completes optimal control.
As shown in figure 4, photovoltaic cell uses Practical mould in figure to use the grid-connected model for improving coordinated control
Type passes through short circuit current Isc, open-circuit voltage Uoc, maximum power electric current ImWith maximum power voltage UmPhotovoltaic cell just can be obtained
Output characteristics.The parameter of model is as shown in table 1.Weight mu and λ equipped with function fluctuation and reactive power fluctuation all take 0.5, k's and γ
Initial value is taken as 0.5, inverter maximum current limit value Iabc max=10A, then passes through the transformed Idq max=10A of Park.
Table 1
Supplemental characteristic and control strategy based on above-mentioned acquisition carry out emulation testing, and test result is as follows：
As shown in figure 5, for the simulation result of fixed k and γ：If simulation time is 2s, a phase voltage is generated in 0.8s
Decline 20%.From Fig. 5 (a) it can be seen that in unbalanced power supply, current harmonics is very big using the control strategy of fixed k and γ
(THD=34.5%) grid-connected requirement is not met, and out-of-limit situation also occurs in maximum current.From Fig. 5 (b) and Fig. 5
(c) result can be seen that active and reactive power fluctuation is very big in unbalanced power supply using the control strategy of fixed k and γ.
As shown in fig. 7, using improved coordination control strategy：Identical with Fig. 5 failure is set, that is, set simulation time as
2s generates a phase voltage decline 20% in 0.8s.The optimum results that control strategy finally obtains be k=0.875, γ=
0.247.Only there is the out-of-limit situation of electric current in instant of failure in electric current from Fig. 7 (a), this is because control strategy is real-time
Optimizing (as shown in Figure 6) is carried out to k and γ, when seeking optimal solution, electric current has been very quick returned within limit value, and measures THD=
4.78%, meet the grid-connected requirement of load.It can be seen that from Fig. 7 (b) and Fig. 7 (c) result using improvement coordination control strategy
In unbalanced power supply, active power and reactive power are stablized in a lesser range after of short duration fluctuation.
To sum up, it using the coordination control strategy with optimizing function, can be sought in the case where guaranteeing that current quality is qualified
The optimal solution asked is power swing minimum, demonstrates the correctness of model.
Above-described specific embodiment has carried out further the purpose of the present invention, technical scheme and beneficial effects
It is described in detail, it should be understood that being not intended to limit the present invention the foregoing is merely a specific embodiment of the invention
Protection scope, all within the spirits and principles of the present invention, any modification, equivalent substitution, improvement and etc. done should all include
Within protection scope of the present invention.
Claims (5)
1. a kind of unbalanced power supply photovoltaic DC-to-AC converter control method for coordinating for considering current limit, which is characterized in that this method packet
Include following steps：
Step 1: the three-phase voltage of acquisition power grid and three-phase current and being coordinately transformed respectively to it, using trapper to warp
The positive and negative order components of voltage and current after coordinate transform extract；
Step 2: the inverter output power under quantization unbalanced power grid, to the active output of influence photovoltaic, idle output and electric current
The amount of harmonic wave is weighted to obtain the weight coefficient k and γ of coordinated control；
Step 3: with active power fluctuation and the minimum optimization aim of reactive power fluctuation, with Current harmonic distortion rate and output
Current limit is that constraint condition optimizes weight coefficient k and γ, building control optimization module；
Step 4: weight coefficient k and the γ optimal value of coordinated control is obtained by the control optimization module of above-mentioned building, to power grid
Uneven photovoltaic DC-to-AC converter carries out coordinated control.
2. a kind of unbalanced power supply photovoltaic DC-to-AC converter control method for coordinating for considering current limit according to claim 1,
It is characterized in that, being specifically included in the step 1：
The three-phase voltage and three-phase current of acquisition power grid simultaneously carry out dq coordinate transform to it respectively；Become using trapper to through coordinate
The positive and negative order components of voltage and current after changing extract to obtain：Positive-sequence component of the three-phase voltage under dq rotating coordinate systemAnd negative sequence componentPositive-sequence component of the three-phase current under dq rotating coordinate systemAnd negative sequence component
Wherein, Ed +、Eq +、Ed -、Eq -Respectively positive-sequence component amplitude and negative sequence component amplitude of the three-phase voltage in d axis and q axis；Id +、
Iq +、Id -、Iq -Respectively positive-sequence component amplitude and negative sequence component amplitude of the three-phase current in d axis and q axis.
3. a kind of unbalanced power supply photovoltaic DC-to-AC converter control method for coordinating for considering current limit according to claim 2,
It is characterized in that, quantifying the inverter output power under unbalanced power grid in the step 2, being embodied as：
When only considering fundamental wave, the network voltage of power grid three-phase imbalance ignores zero-sequence component, then orthogonal just with following formula
Negative sequence component indicates：
The instantaneous active power of inverter grid side is obtained by above-mentioned two formula and the expression formula of reactive power is：
P (t)=P0+Pc2cos(2ωt)+Ps2sin(2ωt)
Q (t)=Q0+Qc2cos(2ωt)+Qs2sin(2ωt)
In formula, P0、Q0Respectively active and idle average value；Pc2、Qc2Respectively secondary active and idle cosine value；Ps2、
Qs2Respectively secondary active and idle sine value；P0、Q0、Pc2、Qc2、Ps2、Qs2Expression formula it is as follows：
It is obtained by above formula, when unbalanced power supply, the output power of inverter also contains second harmonic component in addition to fundametal compoment
And harmonic component；P0、Q0、Pc2、Qc2、Ps2、Qs2Pass through Id +、Id -、Iq +、Iq -The positive and negative order components control of four electric currents.
4. a kind of unbalanced power supply photovoltaic DC-to-AC converter control method for coordinating for considering current limit according to claim 3,
It is characterized in that, being by the reference vector expression formula for being weighted to obtain electric current to control target in 3 in the step 2：
In formula, 0≤k≤1,0≤γ≤1；Different control targets is realized by the change to weight coefficient k and γ.
5. a kind of unbalanced power supply photovoltaic DC-to-AC converter control method for coordinating for considering current limit according to claim 4,
Control optimization module is specifically established using interior point method it is characterized in that, optimizing in the step 3 to weight parameter k and γ：
Use the active power fluctuation exported using photovoltaic DC-to-AC converter and reactive power fluctuation as optimization object function, expression formula is as follows：
min∑μΔP+λΔQ
In formula, Δ P and Δ Q are respectively the undulating value of active power and reactive power, and μ and λ are respectively the weight for being Δ P and Δ Q；
Above-mentioned bound for objective function includes：
A. total harmonic distortion factor：ITHD≤ 5%
In formula, ITHDFor total harmonic distortion factor, its calculation formula is
In formula, I1For the fundametal compoment of electric current, InFor each harmonic component；Total harmonic distortion factor is no more than 5%；
B. current limit constrains：
In formula, IdqFor three-phase transient current IabcTransient current under the dq coordinate system converted through Park, Idq maxIt is grid-connected
Inverter maximum current limit value transforms to be worth under dq coordinate system.
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| CN113742907A (en) * | 2021-08-24 | 2021-12-03 | 国网河南省电力公司电力科学研究院 | Photovoltaic power station short-circuit current unified calculation method |
| CN113742907B (en) * | 2021-08-24 | 2023-09-15 | 国网河南省电力公司电力科学研究院 | Unified calculation method for short-circuit current of photovoltaic power station |
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