CN106712099B - A kind of multi-parallel Design of grid-connected photovoltaic inverter method - Google Patents
A kind of multi-parallel Design of grid-connected photovoltaic inverter method Download PDFInfo
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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
- 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
- H02M7/53—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 using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
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Abstract
The invention discloses a kind of multi-parallel Design of grid-connected photovoltaic inverter methods, comprising the following steps: step 1) finds out the inverter side inductance L of LCL filter1；Step 2) assumes inverter using single inductance L1Filtering designs controller Gc(s), and system open loop cutoff frequency ω at this time is found outc；Step 3) finds out corresponding filter capacitor C1；Step 4) finds out optimal grid side inductance L2, meanwhile, verify fres0Whether it is greater than 10 times of mains frequency, and is less than the half of switching frequency, be such as unsatisfactory for, can return to step 3), adjusts C1Value；Step 5) designs active damping coefficient kd, system open loop transmission function Bode figure is drawn, whether checking system control performance meets the requirements, be such as unsatisfactory for, and adjusts controller Gc(s) parameter.The present invention is able to achieve under different electric network impedances to be stablized grid-connected, and grid-connected current waveform is good, has very strong adaptability to electric network impedance.
Description
Technical field
The present invention relates to circuit fields, more specifically, are related to multi-parallel Design of grid-connected photovoltaic inverter method.
Background technique
As photovoltaic cell cost constantly reduces, photovoltaic power generation technology reaches its maturity, photovoltaic power generation accounts for total power generation specific gravity
It is higher and higher.As the important trend of following photovoltaic development, the distributed power generation of large-sized photovoltaic power station and large capacity mostly uses more
A photovoltaic combining inverter parallel is concentrated grid-connected.Electric network impedance, and operation of power networks are inevitably present in power grid
The change of mode can also cause the variation of electric network impedance.When electric network impedance variation, multi-parallel photovoltaic grid-connected inversion may be caused
The problems such as stability and exceeded grid-connected current harmonic content of device.It is grid-connected inverse that the presence of electric network impedance will affect multi-parallel
The current loop control for becoming device, reduces the phase margin of system, influences the stability of system.
Summary of the invention
In consideration of it, the object of the present invention is to provide a kind of multi-parallel Design of grid-connected photovoltaic inverter methods.
The purpose of the present invention is what is be achieved through the following technical solutions, a kind of multi-parallel Design of grid-connected photovoltaic inverter side
Method, comprising the following steps:
Power P of the step 1) according to system, DC voltage Udc, network voltage ug, switching frequency fsAnd inverter side electricity
Flow liner wave requires η, finds out the inverter side inductance L of LCL filter1；
Step 2) assumes inverter using single inductance L1Filtering designs controller Gc(s), and system open loop at this time is found out
Cutoff frequency ωc；
Step 3) is by resonance frequency omegaresmGreater than ωc, find out corresponding filter capacitor C1；
Step 4) comprehensively considers the filtering performance and cost of LCL filter, finds out optimal grid side inductance L2, meanwhile,
Verify fres0Whether it is greater than 10 times of mains frequency, and is less than the half of switching frequency, be such as unsatisfactory for, can return to step 3), adjusts
Whole C1Value；
Step 5) designs active damping coefficient kd, draw system open loop transmission function Bode figure, checking system control performance
Whether meet the requirements, be such as unsatisfactory for, adjusts controller Gc(s) parameter.
Further, the inverter side inductance L1It obtains by the following method: by formula L1≥Udc ug/4ugPfsObtain L1
Value range.
Further, when inverter is using single inductance L1When filtering, the open-loop transfer function of system is
The Phase margin and power frequency amplitude gain of selecting system, determine controller Gc(s) type and parameter and open-loop cut-off frequency ωc；Its
Middle Gd(s) digitial controller, K are indicatedPWMIndicate inverter bridge gain.
Further, filter capacitor C1 is prepared by the following: by formulaObtain C1Value range；ωcIt indicates
Open-loop cut-off frequency.
Further, when the ripple attenuation multiple of LCL filterWhen maximum, find out
Corresponding grid side inductance L at this time2；The size that capacitance current closed-loop system dampingratioζ is determined by engineering experience, by formulaActive damping coefficient k can be found outd。
By adopting the above-described technical solution, the present invention has the advantage that:
The present invention is able to achieve under different electric network impedances to be stablized grid-connected, and grid-connected current waveform is good, hinders power grid
It is anti-that there is very strong adaptability.
Detailed description of the invention
To make the objectives, technical solutions, and advantages of the present invention clearer, below in conjunction with attached drawing to the present invention make into
The detailed description of one step, in which:
Fig. 1 is multi-parallel photovoltaic combining inverter structure chart；
Fig. 2 is the control structure figure of single-phase photovoltaic grid-connected inverter；
Fig. 3 is the current loop control block diagram of single-phase photovoltaic grid-connected inverter；
Fig. 4 is the equivalent-circuit model of each photovoltaic combining inverter；
Fig. 5 is the equivalent impedance model of multi-parallel photovoltaic combining inverter；
Fig. 6 is the equivalent electric current ring control block diagram of multi-parallel photovoltaic combining inverter；
Fig. 7 is the LCL filter frequency response characteristic under active damping；
Fig. 8 is L1Filtering and LCL filter lower system open loop transmission function Bode figure；
Fig. 9 is the photovoltaic combining inverter equivalent output impedance under different frequency；
Figure 10 is grid entry point voltage and grid-connected current simulation waveform under different electric network impedances；(a)Lg=0, (b) Lg=2mH,
(c)Lg=10mH；
Simulation waveform (L when Figure 11 is 5 inverter parallelsg=2mH), (a) is grid entry point voltage and grid-connected electricity
Waveform is flowed, (b) is power network current waveform.
Specific embodiment
Below with reference to attached drawing, a preferred embodiment of the present invention will be described in detail；It should be appreciated that preferred embodiment
Only for illustrating the present invention, rather than limiting the scope of protection of the present invention.
As shown in Figure 1 it is multi-parallel photovoltaic combining inverter structure chart, has n platform single-phase photovoltaic grid-connected inverter in parallel in figure
Operation, inverter output access power grid by LCL filter.Wherein, uri、i1iAnd i2iRespectively i-th gird-connected inverter it is defeated
Voltage, output electric current and grid-connected current out, L1i、C1iAnd L2iThe inverter side inductance of respectively i-th inverter, filter capacitor and
Net side inductance, Zg=Rg+sLgFor electric network impedance, upccFor grid entry point voltage, ugAnd igRespectively network voltage and power network current.
For multi-parallel three-phase photovoltaic grid-connected inverting device, since three-phase grid-connected inverter is under α β rest frame, two-phase
Between it is mutually indepedent, and current regulator is symmetrical, therefore can be analogous to single-phase grid-connected inverter control.
The detailed control structure of every single-phase photovoltaic grid-connected inverter is as shown in Fig. 2, wherein u in Fig. 1dcFor inverter direct current
Busbar voltage, idcFor input current of inverter.Since the response speed of outer voltage is much smaller than current inner loop response speed, therefore can
DC bus-bar voltage is considered a constant, is Udc, herein only from the friendship between current inner loop angle analysis inverter and power grid
Mutually influence.
Single-phase inversion circuit in Fig. 2 uses typical full bridge structure, urFor inverter bridge output voltage, inverter bridge output is led to
Cross LCL filter access power grid.Phase-locked loop pll exports grid entry point voltage upccSynchronization signal sin θ, current reference signal iref
By reference current amplitude IrefBe multiplied acquisition with sin θ, GcFor current controller, kdFor capacitance current active damping coefficient, inverter
It is modulated using bipolar SPWM.
It is illustrated in figure 3 the current loop control block diagram of single-phase photovoltaic grid-connected inverter, wherein Gc(s) it is passed for current controller
Delivery function, Gd(s) time delay process constituted for digitial controller calculating, sampling and zero-order holder, it is inverse under SPWM modulation
Become bridge gain KPWM=Udc, triangular carrier amplitude is set here as 1.
There are the control delays that one claps for consideration system, are since the open-loop cut-off frequency of grid-connected inverting system is generally much less than
The nyquist frequency of system is described actual numerical calculation delay, sampler and zeroth order using formula (1) in the domain s and kept
Device has enough precision.
T in formula (1)sFor the sampling period of system.
It can be obtained by Fig. 3, the system open loop transmission function under given reference current is
Inverter exports grid-connected current
Wherein G1(s)=[s2L1C1+sGd(s)KPWMkdC1+1]/..[s3L1L2C1+s2Gd(s)KPWMkdL2C1+s(L1+L2)],
I* (s) is the equivalent output current source of inverter, YoIt (s) is inverter effective output admittance.
Assuming that each gird-connected inverter is all made of identical structure, parameter and control strategy in Fig. 1, then each it is grid-connected inverse
The equivalent-circuit model for becoming device is as shown in Figure 4.When n platform photovoltaic combining inverter parallel running, for each gird-connected inverter
For, equally electric network impedance is exaggerated n times.
In conclusion the equivalent impedance model of multi-parallel photovoltaic combining inverter is as shown in figure 5, usually can use this resistance
Anti- model judges whether system stability and system occur resonance.
For inverter equivalent-circuit model shown in Fig. 4, current loop control block diagram is as shown in fig. 6, when no grid entry point
When electric voltage feed forward, electric network impedance is considered as net side inductance L2A part, therefore have L2eq=L2+nLgAnd Rgeq=nRg。
It will be appreciated from fig. 6 that the system open loop transmission function under given reference current is
Wherein G2(s)=Rgeq(1+sGd(s)KPWMkdC1+s2L1C1), G3(s)=s (s2L1L2eqC1+sGd(s)KPWMkdL2eqC1
+L1+L2eq) likewise it is possible to judge the steady of multi-parallel photovoltaic combining inverter using amplitude or Phase margin by formula (4)
It is qualitative.
For multi-parallel photovoltaic combining inverter, stability can be analyzed by equivalent control model, pass through meter
Whether the Phase margin of calculation system is greater than zero, and then judges whether system is in steady operational status.When multi-parallel is grid-connected
When inverter is in critical stable state, there is following formula establishment in Phase margin γ=0 of system:
ω in formula (5)cFor the open-loop cut-off frequency of system.
In the equivalent impedance model of Fig. 5, as inverter output admittance Yo(s) when being matched with equivalent electric network impedance, system
There is resonance phenomena, shown in the condition of impedance matching such as following formula (6).
When impedance matching occurs, for network voltage, system is in series resonance state, if network voltage at this time
In the harmonic voltage component containing respective frequencies, grid-connected current i2In can generate a large amount of harmonic current, influencing inverter just
Often operation.
When impedance matching occurs, for the equivalent output current source of inverter, system is in parallel resonance state,
But since I* (s) is an ideal fundamental current source in impedance model, and parallel resonance is equivalent to " open circuit ", therefore system
Parallel resonance can't make the harmonic current in grid-connected current be amplified.
From the above analysis, when multi-parallel photovoltaic combining inverter is in critical stable state, there is formula (5) establishment, pass through
It derives and calculates, detailed derivation process is as follows:
As G'(s)=- 1 when,
I.e.
That is Gc(s)Gd(s)KPWM+G2(s)+G3(s)=0
I.e.
Gc(s)Gd(s)KPWM+s3L1L2C1+s2Gd(s)KPWMkdL2C1+sL1+sL2+(nRg+snLg)(s2L1C1+sGd(s)
KPWMkdC1+ 1)=0 it is
I.e.
System meets impedance matching condition at this time, i.e. formula (7) is set up, and the frequency of impedance matching is the open loop cut-off of system
Frequency.
If inverter effective output admittance has following form:
Then system is set up just like drawing a conclusion:
1) as the γ of system G ' (s)=0, there must be R (ωc)+nRg=0 and X (ωc)+nωcLg=0 sets up, this is formula
(7) conclusion；Meanwhile there is R (ω1)+nRg≠ 0 and X (ω1)+nω1Lg=0 sets up, here ω1It may not be unique, it is also possible to no
In the presence of.
2) as the γ of system G ' (s) ≠ 0, there is R (ω2)+nRg≠ 0 and X (ω2)+nω2Lg=0 sets up, similarly, this
In ω2It may not be unique, it is also possible to be not present；Meanwhile a certain frequencies omega must be not presentx, so that R (ωx)+nRg=0 and X (ωx)
+nωxLg=0 sets up, and the easy-to-use reduction to absurdity of this conclusion is demonstrate,proved, if above-mentioned ωxIn the presence of must then there is system G ' (s) Phase margin at this time
γ=0.
In summary, the multi-parallel photovoltaic synchronization inverter system determining for one, equation X (ω)+n ω Lg=0
Root may be not present, it is also possible to have it is multiple, when there are a root ω, so that meeting R (ω)+nR simultaneouslygWhen=0, system G ' (s)
Phase margin be zero, and this root ω=ωc。
In the equivalent impedance model of Fig. 5, the network voltage of distortion can be in grid-connected current i2It is middle to generate corresponding harmonic wave electricity
Stream.
U in formula (9)ghFor the h subharmonic voltage in network voltage, i2hFor the h subharmonic current in grid-connected current.
By Such analysis, when system γ=0, there is R (ω)+nRg=0 and X (ω)+n ω Lg=0 sets up, simultaneously because R
(ω) and X (ω) are to convert to obtain by limited times by elementary function, therefore R (ω) and X (ω) are continuous function, therefore
Have
Certainly, the frequencies omega in formula (10) should approach or equal to system open-loop cut-off frequency ωc, the frequency of harmonic voltage
It also should be near said frequencies.By formula (10) it is found that prevent network voltage distortion from generating harmonic pollution, Ying Bao to grid-connected current
Card system G ' (s) has certain Phase margin.
Inverter bridge link under SPWM modulation is a nonlinear element, output voltage harmonic components rich in,
It specifically includes that the low-order harmonics voltage such as 3,5,7 caused by dead zone, and modulates the high order at the switching frequency generated and its frequency multiplication
Harmonic voltage.In equivalent control model shown in Fig. 6, inverter bridge exports urIn contain above-mentioned harmonic components, with urIt is defeated
Enter, grid-connected current i2It is for the closed loop transfer function, of output
When the Phase margin of system G ' (s) levels off to zero, then have
Certainly, the transmission function G ' (s) in formula (11) and (12) is approximate obtains, when consideration inverter bridge link output is humorous
When wave voltage, inverter bridge link is exactly that inverter bridge (is equivalent to proportional gain K in Fig. 6 by a nonlinear elementPWM), but usually
Switching frequency is sufficiently high, therefore above-mentioned approximate with enough accuracy.It is not difficult to find out by formula (12), when the phase angle of system G ' (s) is abundant
When spending lower, urIn harmonic voltage can generate biggish harmonic pollution to grid-connected current, therefore, in order to improve grid-connected current
Power quality should ensure that system G ' (s) has certain Phase margin.
Formula (11) and the frequency of harmonic voltage and electric current in (12) are near system open loop cutoff frequency, frequency rank
It is secondary relatively low, as the γ of system G ' (s)=0, claim system to be in " low-frequency resonant " state at this time.And inverter bridge is exported
Higher harmonic voltage, usually using LCL filter progress harmonics restraint, when the damping strategy fails of LCL filter, system
" high-frequency resonant " can occur, so that grid-connected current distortion is serious.
In conclusion working as inverter bridge link output harmonic wave voltage, and when power grid contains background harmonic voltage, in order to reduce simultaneously
Harmonic content in net electric current it is enough should to guarantee that system G ' (s) has under the premise of LCL filter damps strategy and do not fail
Stability margin.
By Such analysis, in order to guarantee the power quality of grid-connected current, multi-parallel photovoltaic combining inverter should have enough
Stability margin, particularly, when equivalent electric network impedance changes, it is desirable that system has enough Phase margins always.By
Resistive component in electric network impedance can increase the Phase margin of system, improve system stability, therefore this section considers extremely
Situation only contains inductive component in electric network impedance.
Each producer does not take into account that the influence of electric network impedance usually when designing and producing photovoltaic combining inverter, and works as
When considering that electric network impedance influences, photovoltaic combining inverter should carry out analysis and design using the electric current loop in Fig. 6.Carefully relatively scheme
3 and Fig. 6, it is not difficult to find that due to the presence of electric network impedance, so that the equivalent net side filter inductance of LCL filter is changed,
And then LCL filter also changes phase angle contribution of the system G ' (s) at cutoff frequency.
Formula (13) is the relational expression that the resonance frequency of LCL filter changes with equivalent electric network impedance, with nLgIncrease,
Resonance frequency omegaresIt is gradually reduced.Fig. 7 show the LCL filter frequency response characteristic under active damping control, in resonance frequency
Near rate, the phase-frequency characteristic of LCL filter changes to -270 ° by -90 ° rapidly.
With the continuous reduction of LCL filter resonance frequency, work as ωresMove closer to the open-loop cut-off frequency ω of systemc
When, LCL filter changes to -270 ° by -90 ° rapidly to the phase angle contribution of system G ' (s), this makes the Phase margin of system fast
Speed reduces, and system is intended to unstable.In conclusion the increase of inductive component in equivalent electric network impedance is explained, so that system
The reason of stability reduces.
Known by formula (14), ωresThere are a minimum ωresm.Therefore, when equivalent electric network impedance changes, in order to prevent
Phase-frequency characteristic at LCL filter resonance frequency has an impact system stability, can be with design parameter L1And C1, so that ωresm
Greater than system open loop cutoff frequency, in this way under different electric network impedances, LCL filter is in ωcPlace is contributed by the phase angle of system
It is always -90 °.
If equivalent electric network impedance is 0, the resonance frequency of LCL filter is ωres0, then ωres0With ωresmRelative mistake
Value is
By mathematical knowledge it is found that δresIt is about L1/L2Increasing function.Assuming that L1And L2The order of magnitude having the same, i.e. L1/
L2∈ [0.1,10], then have δres∈ [4.65%, 69.8%].Particularly, work as L1=L2When, δres=29.3%.Therefore, when etc.
When imitating electric network impedance variation, in order to reduce the mobile range of LCL filter resonance frequency, in design parameter L1And L2When, it can be
Under the premise of not influencing filter filtering performance, lesser L is selected as far as possible1/L2。
In fact, the variation range of actual electric network impedance is limited, it is impossible to be infinitely great, LCL filter resonance frequency
Movement is also very limited.Therefore, resonance frequency omega is designedres0It is particularly important, as previously mentioned, needing to design ωres0Greater than system
Open-loop cut-off frequency ωc, to improve system to the anti-interference ability of electric network impedance.
The present invention proposes a kind of multi-parallel Design of grid-connected photovoltaic inverter method, comprising the following steps:
1) according to the power P of system, DC voltage Udc, network voltage ug, switching frequency fsAnd inverter side electric current line
Wave requires η, finds out the parameter L of LCL filter1；
2) assume inverter using single inductance L1Filtering designs controller Gc(s), and find out at this time system open loop cut-off
Frequencies omegac；
3) by resonance frequency omegaresmGreater than ωc, find out corresponding filter capacitor C1；
4) filtering performance and cost for comprehensively considering LCL filter, find out optimal L2, meanwhile, verify fres0Whether it is greater than
10 times of mains frequency, and it is less than the half of switching frequency, it is such as unsatisfactory for, can return to step 3), appropriate adjustment C1Value；
5) active damping coefficient k is designedd, system open loop transmission function Bode figure is drawn, whether is checking system control performance
It meets the requirements, is such as unsatisfactory for, it can appropriate adjustment controller Gc(s) parameter.
By above-mentioned design, under different electric network impedances, for the control of the low-frequency range of inverter, equally system begins
L-type filter is used eventually, this is also the cause of inverter " strong ".
There is document to have been pointed out, with the increase of equivalent electric network impedance, the damping ratio of LCL filter is gradually increased, and therefore, is
System will not because of active damping strategy failure and high-frequency resonant occurs.
The present embodiment illustrates the design method of inverter with specific parameter
1) output power of single-phase photovoltaic grid-connected inverter is set as 5kW, DC voltage 400V, network voltage virtual value
220V, switching frequency 10kHz, it is desirable that inverter side current ripples are no more than 15%, then inverter side inductance L1>=2.9mH, this
In choose L1=3mH.
2) when inverter is using single inductance L1When filtering, select current controller for PR control, parameter kp=0.06, kr=
0.1, the Bode of system open loop transmission function schemes as shown in figure 8, cutoff frequency ωc=5960rad/s.
3) work as ωresmGreater than ωcWhen, C1< 9.4 μ F, take C here1=4.7 μ F.
4) LCL filter ripple attenuation multiple with higher at switching frequency is required, and controls cost, takes L2=
2mH.F at this timeres0=2119Hz, meets the requirements.
5) active damping coefficient k is chosend=0.15, the complete open-loop transfer function Bode figure of system is as shown in figure 8, cut-off
Frequencies omega 'c=3670rad/s, Phase margin are 45 °, and system has preferable control performance.
As shown in figure 8, system equally uses single inductor filter (inductance value L=L in low-frequency range1+L2), due to ω 'c<
ωc, this is but also resonance frequency omegaresmFarther away from system open loop cutoff frequency.
By numerical value software for calculation, the photovoltaic combining inverter equivalent output impedance under different frequency, such as Fig. 9 can be calculated
It is shown.Since resonance controlling unit only has larger impact to the output impedance at power frequency, in Fig. 9, ratio is only accounted for
Control.When frequencies omega ∈ (0,3370), X (ω) < 0, due to the uncertainty of electric network impedance, equation X (ω)+n ω L at this timeg
=0 may be with the presence of solution, but in the frequency range, R (ω) > 11.47, by formula (9) it is found that the harmonic wave in network voltage understands quilt
Decaying inhibits.As frequencies omega > 30000rad/s, R (ω) ≈ 0, X (ω) are much larger than 0, and the harmonic wave in network voltage can still be declined
Subtract inhibition.In summary, due to the high stability of system, even if resonance phenomena has occurred because of impedance matching, due to being
The damping action of system is stronger, Harmonics amplification will not occurs.
Above-mentioned single-phase photovoltaic grid-connected inverter model is built in MATLAB, the structure of inverter and control are as shown in Figure 2.
5,7,9,11,13 subharmonic each 1% are injected in ideal network voltage, and when single inverter is incorporated into the power networks, power grid is set
Impedance is respectively 0,2mH and 10mH, and the simulation waveform of grid entry point voltage and grid-connected current is as shown in Figure 10, is shown for convenience,
Grid entry point voltage is reduced 5 times.
As shown in Figure 10, under different electric network impedances, single-phase photovoltaic grid-connected inverter is in steady-working state always,
And grid-connected current waveform is preferable.Fft analysis is carried out to grid-connected current, percent harmonic distortion is respectively 3.44%, 3.15% and
2.71%, Current harmonic distortion rate is gradually reduced, and is because electric network impedance can regard a part of LCL filter net side inductance as.
Due to containing low-order harmonic in network voltage, and harmonic compensation link is not added in current controller, therefore grid-connected current is humorous
Low-order harmonic accounts for major part in wave.
By above-mentioned identical 5 inverter parallels, as shown in Figure 1, setting electric network impedance is 2mH, grid entry point voltage,
The simulation waveform of grid-connected current and power network current is as shown in figure 11.When more inverter parallels, grid-connected current and electricity
The equal waveform of net electric current is good, there is no harmonic resonance and wild effects, it was demonstrated that above-mentioned design it is single-phase photovoltaic grid-connected
Inverter is enough " strong ".
The above description is only a preferred embodiment of the present invention, is not intended to restrict the invention, it is clear that those skilled in the art
Various changes and modifications can be made to the invention by member without departing from the spirit and scope of the present invention.If in this way, of the invention
Within the scope of the claims of the present invention and its equivalent technology, then the present invention is also intended to encompass these to these modifications and variations
Including modification and variation.
Claims (4)
1. a kind of multi-parallel Design of grid-connected photovoltaic inverter method, it is characterised in that: the following steps are included:
Power P of the step 1) according to system, DC voltage Udc, network voltage ug, switching frequency fsAnd inverter side electric current line
Wave requires η, finds out the inverter side inductance L of LCL filter1, calculation formula are as follows: L1≥Udc ug/4ηPfs；
Step 2) assumes inverter using single inductance L1Filtering designs controller Gc(s), and find out at this time system open loop cut-off
Frequencies omegac；Step 3) by resonance frequency minimum ωresmGreater than ωc, find out corresponding filter capacitor C1；
Step 4) comprehensively considers the filtering performance and cost of LCL filter, finds out optimal grid side inductance L2, meanwhile, verification
ωres0Whether it is greater than 10 times of mains frequency, and is less than the half of switching frequency, be such as unsatisfactory for, can return to step 3), adjusts C1
Value；Wherein, ωres0Be equivalent electric network impedance be 0 when, the resonance frequency of LCL filter；
Step 5) designs active damping coefficient kd, system open loop transmission function Bode figure is drawn, whether checking system control performance is full
Foot requires, and is such as unsatisfactory for, and adjusts controller Gc(s) parameter.
2. a kind of multi-parallel Design of grid-connected photovoltaic inverter method according to claim 1, it is characterised in that: work as inverter
Using single inductance L1When filtering, the open-loop transfer function of system isThe Phase margin and work of selecting system
Frequency amplitude gain determines controller Gc(s) type and parameter and open-loop cut-off frequency ωc；Wherein Gd(s) digitial controller is indicated,
KPWMIndicate inverter bridge gain.
3. a kind of multi-parallel Design of grid-connected photovoltaic inverter method according to claim 1, it is characterised in that: filter capacitor
C1It is prepared by the following: by formulaObtain C1Value range；ωcIndicate open-loop cut-off frequency.
4. a kind of multi-parallel Design of grid-connected photovoltaic inverter method according to claim 1, it is characterised in that: when LCL is filtered
The ripple attenuation multiple of wave deviceWhen maximum, corresponding grid side inductance L at this time is found out2；
The size for determining filter capacitor current closed-loop system damping ratio ζ, by formulaFind out active damping system
Number kd。
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| CN111245004B (en) * | 2018-11-28 | 2023-06-16 | 哈尔滨工业大学 | Composite robust control method of high-frequency SiC photovoltaic grid-connected inverter under weak current network |
| CN109842153A (en) * | 2019-01-29 | 2019-06-04 | 国网河南省电力公司电力科学研究院 | The LCL parameter and control parameter design method and device of raising electric network impedance adaptability |
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| CN110867856A (en) * | 2019-11-28 | 2020-03-06 | 国网河南省电力公司驻马店供电公司 | LCL filter parameter optimization method under condition of considering VSC system harmonic stability |
| CN112271750B (en) * | 2020-10-13 | 2022-06-17 | 上海海事大学 | Method for identifying internal unstable inverter in multi-parallel inverter system |
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| CN113224791B (en) * | 2021-05-07 | 2023-11-21 | 苏州海鹏科技有限公司 | Virtual impedance active damping control method for grid-connected inverter |
| CN113991658B (en) * | 2021-11-02 | 2024-07-05 | 国网北京市电力公司 | Power equipment control method and device |
| CN116191457B (en) * | 2023-04-27 | 2023-09-12 | 中山大学 | Active damping control method of DSTATCOM under weak current network |
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