CN105914774B - A kind of multiple combining inverters for considering dead band large-sized photovoltaic grid-connected system modeling method in parallel - Google Patents
A kind of multiple combining inverters for considering dead band large-sized photovoltaic grid-connected system modeling method in parallel Download PDFInfo
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- H02J3/383—
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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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Abstract
The invention discloses a kind of multiple combining inverters for considering dead band large-sized photovoltaic grid-connected system modeling method in parallel, comprise the following steps：S1. the influence in dead band is considered in modeling, obtains the relation between each voltage component of Inverter Dead-time distorted voltage and the preferable fundamental voltage of inverter output；S2. the fundamental wave of dead band distorted voltage and introduced low-order harmonic composition are added in the impedance model of photovoltaic parallel in system by Laplace transform, so as to obtain the impedance model of single grid-connected inverters system；S3. according to the impedance model of single grid-connected inverters system, obtain the equivalent circuit of multiple combining inverters large-sized photovoltaic grid-connected system in parallel and draw the output impedance of photovoltaic plant side.The present invention provides reference to analyze the analysis of the stability and the quality of power supply of large-sized photovoltaic grid-connected system when electric network impedance changes and improvement.
Description
Technical field
The present invention relates to technical field of photovoltaic power generation, and in particular to a kind of multiple combining inverters parallel connection for considering dead band
Large-sized photovoltaic grid-connected system modeling method.
Background technology
As traditional energy constantly consumes the cleaning renewable energy such as the energy shortage brought and problem of environmental pollution, solar energy
Source has obtained huge development.The planning of National Energy Board 13 shows that, to the year two thousand twenty bottom, solar power generation installed capacity will reach
To 1.6 hundred million kilowatts, it is about 200,000,000,000 yuan that annual electricity generating capacity, which is up to 170,000,000,000 kilowatt hours and annual gross investment,.It is noticeable
It is, wherein, photovoltaic generation total installation of generating capacity is up to 1.5 hundred million kilowatts.Photovoltaic plant also can gradually tend to maximize, photovoltaic plant
Capacity will be continuously increased, to the quality of power supply and the stability of a system requirement will be stricter.Moreover, substantial amounts of inverter parallel
Power network equiva lent impedance will be made to become big, further influence the stability of photovoltaic plant.In addition, in order to prevent inverter upper and lower bridge arm
Straight-through phenomenon, have to inject certain dead time in the control signal of switching device, the introducing in dead band will trigger inverse
Become the distortion of device output waveform, reduce fundamental voltage, introduce compared with low-order harmonic composition, when photovoltaic plant output impedance and power network hinder
The anti-resonance that can trigger when matching between large-sized photovoltaic power station and power network, and then influence the output quality of power supply and stably of system
Property.Therefore, it is necessary to take into account dead time effect when analyzing the stability of large-sized photovoltaic grid-connected system, and present analysis light
The main stream approach for lying prostrate grid-connected system stability is Impedance Analysis, it is therefore necessary to which dead band is built in the impedance model of system
Go.Some document analysises dead time effect of inverter simultaneously proposes compensation technique.Some is to single-phase photovoltaic grid-connected system
The influence of dead time effect is embodied in the impedance model of foundation, but at the non-linear factor not introduced to dead time effect
Reason, really dead band is not established into impedance model.Some considers higher hamonic wave and dead band caused by PWM effect
The low-order harmonic that effect introduces is seen to the equivalent error voltage for influenceing but dead band being acted on and formed of inverter output voltage
Into the part of power supply, it is not embodied among impedance model.
The content of the invention
In consideration of it, it is an object of the invention to provide a kind of multiple combining inverters for considering dead band large-sized photovoltaic in parallel simultaneously
Net system modeling method.
The purpose of the present invention is achieved through the following technical solutions,
A kind of multiple combining inverters for considering dead band large-sized photovoltaic grid-connected system modeling method in parallel, including following step
Suddenly：
S1. the influence in dead band is considered in modeling, each voltage component of Inverter Dead-time distorted voltage is obtained and inverter is defeated
The relation gone out between preferable fundamental voltage；
S2. the fundamental wave of dead band distorted voltage and introduced low-order harmonic composition are added to by photovoltaic by Laplace transform
In the impedance model of grid-connected system, so as to obtain the impedance model of single grid-connected inverters system；
S3. according to the impedance model of single grid-connected inverters system, multiple combining inverters large-sized photovoltaic in parallel is obtained
The equivalent circuit of grid-connected system and the output impedance for drawing photovoltaic plant side.
Further, the step S1 includes following sub-step：
The relation for the preferable fundamental voltage that distorted voltage each voltage component in Inverter Dead-time exports with inverter is in frequency domain：
Wherein, G1, G5, G7The fundamental wave of dead band distorted voltage, the biography between 5 times and 7 subharmonic and desired voltage are represented respectively
Delivery function.Represent the fundamental wave of dead band distorted voltage5 subharmonic of dead band distorted voltage are represented,Represent that dead band is abnormal
7 subharmonic of time variant voltage, ursThe preferable fundamental voltage of inverter output is represented, m and n are respectively dead band distorted voltage and desired electrical
The amplitude of pressure, angles of the θ between dead band distorted voltage and desired voltage, φ0Desired voltage fundamental wave first phase is exported for inverter
Angle, ω are fundamental wave angular frequency.
Further, the impedance model of large-sized photovoltaic grid-connected system obtains step：
S31. Fourier transformation is carried out to three-phase dead band distorted voltage；
S32. take the fundamental wave of Fourier's expression formula, 5 times and 7 subharmonic to be transformed into α β axles and combine step S31 change
Change result and draw single grid-connected inverters system control block figure；
S33. grid-connected system is obtained according to single grid-connected inverters system control block figure and transformer with split winding equivalent inductance Lt
Equivalent circuit；
S34. the large-sized photovoltaic grid-connected system equivalent circuit that N number of combining inverter is in parallel is obtained；
S35. equivalent predigesting is carried out to large-sized photovoltaic grid-connected system, obtains the Norton equivalent of whole large-sized photovoltaic grid-connected system
Circuit, further obtain the output impedance of large-sized photovoltaic grid-connected system.
By adopting the above-described technical solution, the present invention has the advantage that：
The present invention establishes Inverter Dead-time effect into the impedance model of system when changing for analysis electric network impedance greatly
The analysis and improvement of the stability and the quality of power supply of type photovoltaic parallel in system provide reference.
Brief description of the drawings
In order that the object, technical solutions and advantages of the present invention are clearer, the present invention is made below in conjunction with accompanying drawing into
The detailed description of one step, wherein：
Fig. 1 is three-phase inverting circuit schematic diagram；
Fig. 2 is iaDrive signal and output voltage waveform during ＞ 0；
Fig. 3 is that dead band influences vectogram to fundamental wave；
Fig. 4 is consideration dead band current inner loop control block diagram；
Fig. 5 is combining inverter equivalent circuit；
Fig. 6 is large-sized photovoltaic grid-connected system equivalent circuit；
Fig. 7 is large-sized photovoltaic grid-connected system equivalent circuit；
Fig. 8 is large-sized photovoltaic system output impedance waveform；
Fig. 9 is current transfer function root locus；
Figure 10 is nyquist diagram when N changes；
Figure 11 is nyquist diagram partial enlarged drawing.
Embodiment
Below with reference to accompanying drawing, the preferred embodiments of the present invention are described in detail；It should be appreciated that preferred embodiment
Only for the explanation present invention, the protection domain being not intended to be limiting of the invention.
The normal work of inverter circuit, typically to give the control signal of switching device plus certain dead time so that anti-
The only straight-through phenomenon of inverter upper and lower bridge arm, although the very short low-order harmonic accumulation effect caused by it of added dead time
The quality of power supply should will be influenceed, particularly will make grid-connected current wave distortion serious in large-sized photovoltaic grid-connected system, is influenceed
The stable operation of system.
As shown in figure 1, for convenience of analyzing, the DC side of inverter is equivalent to the series connection of two electric capacity, each electric capacity
Voltage is U for the half of DC voltagedc/2.If dead time is td, the switch device conductive time is ton, the turn-off time is
toff, switch periods Ts, by taking a phase bridge arms as an example, as a phase currents iaDuring ＞ 0, a phases switching pulse and inverter output voltage ripple
Shape is as shown in Figure 2.
The actual output voltage U of inverteraNrDesired output voltage U can be equivalent toaNiWith dead band distorted voltage Δ UaN's
Superposition value is：
UaNr=UaNi+ΔUaN (1)
Because switching frequency is much larger than fundamental frequency, dead zone voltage can be taken to the average value in a cycle, can by Fig. 2
To draw a, the distorted voltage Δ U between N 'aN’For：
Wherein：
B phases and c phase distortion voltage Δs U can similarly be drawnbN’, Δ UcN’Expression formula：
Three-phase dead band distorted voltage Δ U can be obtained by Fig. 1aN, Δ UbN, Δ UcNExpression formula：
N can be drawn by (6) formula, the voltage Δ U between N 'NN’For：
Simultaneous (2)-(6) formula obtains a phases dead band distorted voltage Δ UaNFor：
Wherein：
Td=td+ton-toff
As can be seen that coupled relation be present between inverter output dead band distorted voltage three-phase, and only with three-phase current
Direction is relevant.For ease of analysis, to three-phase dead band distorted voltage Δ UaN, Δ UbN, Δ UcNFourier decomposition is carried out to obtain：
Wherein：N=6k ± 1, k=0,1,2 ...
Dead band can introduce 57 inferior low-order harmonics it can be seen from Fourier decomposition expression formula, and can also be to fundamental wave
Produce considerable influence, due to the amplitude of dead time effect introduced 11 times and above higher hamonic wave with the increase of overtone order and by
Filter action decrescence small and in view of LCL filter, the present embodiment only build the fundamental wave of dead band distorted voltage and low-order harmonic
Stand into the impedance model of large-sized photovoltaic grid-connected system.
There is difference in amplitude and phase between distorted voltage fundamental wave and desired voltage caused by dead time effect.Such as Fig. 3
Shown, the phase difference of inverter output current and dead band distorted voltage is 180 °, and actual output voltage and electric current angle are load
Power-factor angleAngle between electric current and desired voltage is
For the amplitude of dead band distorted voltage relative to the amplitude very little of fundamental voltage, the present embodiment can be approximate by desired voltage
Angle between electric current regards the angle between virtual voltage and electric current, i.e. power-factor angle as.Therefore for High Power Factor
Inverter for the influence of dead time effect will be more serious.If the angle between dead band distorted voltage and desired voltage is：
If the fundamental voltage u of inverter outputrAmplitude is n, initial phase angle φ0, then expression formula be：
ur=nsin (ω t+ φ0) (13)
The fundamental wave of dead band distorted voltage, 5 times and 7 subharmonic expression formulas are：
Δu1=m sin (ω t+ φ0+θ) (14)
Δu5=m sin (5 ω t+5 (φ0+θ)) (15)
Δu7=m sin (7 ω t+7 (φ0+θ)) (16)
Then distorted voltage each voltage component in dead band is with the preferable fundamental voltage transmission function of inverter output in a frequency domain：
Inverter Dead-time distorted voltage have found by analysis above and export the relation between desired voltage, so just
Dead time effect can be established into the impedance model of large-sized photovoltaic grid-connected system.According to the expression of three-phase dead band distorted voltage
Formula, carried out Fourier transformation such as formula (9), (10), shown in (11), because the present embodiment only considers low-order harmonic, take in Fu
The fundamental wave of leaf expression formula, 5 times and 7 subharmonic are transformed into α β axles and obtain its expression formula：
Convolution (17)-(19), large-sized photovoltaic grid-connected system control block diagram can be drawn：Fig. 4 is wherein：Given value of current
Value, isαβ：Grid-connected current, Gc(s)：The transmission function of PR controllers, kc：Realize the active damping of capacitance current, Usαβ：Power network electricity
Pressure, L1, L2For filter inductance, C is filter capacitor.
Kpwm=kpwm(1+G1+G5+G7)
Wherein KpwmTo consider the equivalent link of inverter behind dead band, kpwmRepresent ideal conditions modulated ripple to the biography of output
Delivery function, represent in bracket to consider the transmission function of dead band distorted voltage.So as to which just dead time effect has been built in control block diagram.
By can obtain (21) formula to block diagram abbreviation：
Wherein：
Transformer with split winding equivalent inductance L is considered further that by formula (21)tObtain single grid-connected inverters system equivalent circuit
Such as Fig. 5.
Wherein grid-connected current IpvWith the output admittance Y of systempvExpression formula is as follows：
So as to obtain large-sized photovoltaic grid-connected system equivalent circuit such as Fig. 6 that N number of combining inverter is in parallel：
Equivalent predigesting is carried out to large-sized photovoltaic grid-connected system, can obtain the Norton equivalent electricity of whole large-sized photovoltaic grid-connected system
Road such as Fig. 7.
Output admittance by the available large-sized photovoltaic grid-connected systems seen into by grid side of Fig. 7 is：
Systematic parameter is as shown in table 1, by system output admittance it is inverted obtain add dead band before and after output impedance ripple such as Fig. 8
It is shown, it can be seen that to have significantly in lower frequency region plus output impedance waveform behind dead band and the output impedance waveform for being not added with dead band
Difference, the wild effect for causing system is easier when identical electric network impedance changes.
The photovoltaic parallel in system parameter of table 1
Whole large-sized photovoltaic grid-connected system grid-connected current I can obtain by Fig. 8sExpression formula：
It can be seen that the stability of large-sized photovoltaic grid-connected system is made up of two parts, must meet first steady inside photovoltaic plant
Surely it is current transfer function G/ (1+YeqsLt) do not include RHP limit.Secondly, can be by right the half of grid-connected current expression formula
Regard the closed loop transfer function, expression formula that forward gain is 1, i.e. 2NY as in partpv/YgMeet Nyquist stability criterion.
The internal stability for knowing photovoltaic plant by current transfer function is influenceed by transformer with split winding equivalent inductance, according to
Parameter listed by table 1, Fig. 9 are the root locus diagram of current transfer function when transformer with split winding equivalent inductance changes, it can be seen that only
In LtMeet the stabilization that system is just can guarantee that during certain limit.To equivalent open-loop transfer function when changing with regard to photovoltaic plant capacity N
That is 2NYpv/YgNyquist diagram is drawn, as shown in Figure 10, Figure 11 is partial enlarged drawing.As seen from Figure 11, as N=1 or N
System is stable when=2, and as N=3, nyquist plot surrounds (- 1, j0) point, i.e., wild effect occurs in system.
The present invention establishes Inverter Dead-time into the impedance model of photovoltaic parallel in system, labor Inverter Dead-time
Influence to output waveform, the equivalent circuit of large-sized photovoltaic grid-connected system is shifted out onto.When comparative analysis whether there is dead band
The output impedance expression formula that large-sized photovoltaic grid-connected system is seen into by grid side, and according to the modulus of impedance of large-sized photovoltaic grid-connected system
Type derives the expression formula of grid-connected current, using impedance analysis method with regard to photovoltaic plant capacity analysis large-sized photovoltaic grid-connected system
Stability, and give stability distinguishing condition.The stability of large-sized photovoltaic grid-connected system when changing for analysis electric network impedance
And the analysis and improvement of the quality of power supply provide reference.
The preferred embodiments of the present invention are the foregoing is only, are not intended to limit the invention, it is clear that those skilled in the art
Member can carry out various changes and modification without departing from the spirit and scope of the present invention to the present invention.So, if the present invention
These modifications and variations belong within the scope of the claims in the present invention and its equivalent technologies, then the present invention is also intended to include these
Including change and modification.
Claims (2)
- A kind of 1. multiple combining inverters for considering dead band large-sized photovoltaic grid-connected system modeling method in parallel, it is characterised in that： Comprise the following steps：S1. the influence in dead band is considered in modeling, each voltage component of Inverter Dead-time distorted voltage is obtained and is managed with inverter output Think the relation between fundamental voltage；S2. the fundamental wave of dead band distorted voltage and introduced low-order harmonic composition are added to by Laplace transform grid-connected In the impedance model of system, so as to obtain the impedance model of single grid-connected inverters system；S3. according to the impedance model of single grid-connected inverters system, it is grid-connected to obtain multiple combining inverters large-sized photovoltaic in parallel The equivalent circuit of system and the output impedance for drawing photovoltaic plant side；The step S1 includes following sub-step：The relation for the preferable fundamental voltage that distorted voltage each voltage component in Inverter Dead-time exports with inverter is in frequency domain：<mrow> <msub> <mi>C</mi> <mn>1</mn> </msub> <mo>=</mo> <mfrac> <mrow> <msubsup> <mi>&Delta;u</mi> <mi>s</mi> <mn>1</mn> </msubsup> </mrow> <msub> <mi>u</mi> <mrow> <mi>r</mi> <mi>s</mi> </mrow> </msub> </mfrac> <mo>=</mo> <mfrac> <mi>m</mi> <mi>n</mi> </mfrac> <mo>(</mo> <mrow> <mi>cos</mi> <mrow> <mo>(</mo> <mi>&theta;</mi> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <mrow> <mi>s</mi> <mi> </mi> <mi>cos</mi> <mrow> <mo>(</mo> <msub> <mi>&phi;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mi>sin</mi> <mrow> <mo>(</mo> <mi>&theta;</mi> <mo>)</mo> </mrow> <mo>-</mo> <mi>&omega;</mi> <mi>sin</mi> <mrow> <mo>(</mo> <msub> <mi>&phi;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mi>sin</mi> <mrow> <mo>(</mo> <mi>&theta;</mi> <mo>)</mo> </mrow> </mrow> <mrow> <mi>&omega;</mi> <mi>cos</mi> <mrow> <mo>(</mo> <msub> <mi>&phi;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mo>+</mo> <mi>s</mi> <mi> </mi> <mi>sin</mi> <mrow> <mo>(</mo> <msub> <mi>&phi;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> </mrow> </mfrac> </mrow> <mo>)</mo> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>17</mn> <mo>)</mo> </mrow> </mrow><mrow> <msub> <mi>C</mi> <mn>5</mn> </msub> <mo>=</mo> <mfrac> <mrow> <msubsup> <mi>&Delta;u</mi> <mi>s</mi> <mn>5</mn> </msubsup> </mrow> <msub> <mi>u</mi> <mrow> <mi>r</mi> <mi>s</mi> </mrow> </msub> </mfrac> <mo>=</mo> <mfrac> <mi>m</mi> <mrow> <mn>5</mn> <mi>n</mi> </mrow> </mfrac> <mo>(</mo> <mfrac> <mrow> <mi>s</mi> <mi> </mi> <mi>sin</mi> <mrow> <mo>(</mo> <mn>5</mn> <mi>&theta;</mi> <mo>+</mo> <mn>5</mn> <msub> <mi>&phi;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mo>+</mo> <mn>5</mn> <mi>&omega;</mi> <mi>cos</mi> <mrow> <mo>(</mo> <mn>5</mn> <mi>&theta;</mi> <mo>+</mo> <mn>5</mn> <msub> <mi>&phi;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> </mrow> <mrow> <mi>&omega;</mi> <mi>cos</mi> <mrow> <mo>(</mo> <msub> <mi>&phi;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mo>+</mo> <mi>s</mi> <mi> </mi> <mi>sin</mi> <mrow> <mo>(</mo> <msub> <mi>&phi;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>)</mo> <mo>&CenterDot;</mo> <mfrac> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <msup> <mi>&omega;</mi> <mn>2</mn> </msup> </mrow> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>25</mn> <msup> <mi>&omega;</mi> <mn>2</mn> </msup> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>18</mn> <mo>)</mo> </mrow> </mrow><mrow> <msub> <mi>G</mi> <mn>7</mn> </msub> <mo>=</mo> <mfrac> <mrow> <msubsup> <mi>&Delta;u</mi> <mi>s</mi> <mn>7</mn> </msubsup> </mrow> <msub> <mi>u</mi> <mrow> <mi>r</mi> <mi>s</mi> </mrow> </msub> </mfrac> <mo>=</mo> <mfrac> <mi>m</mi> <mrow> <mn>7</mn> <mi>n</mi> </mrow> </mfrac> <mo>(</mo> <mfrac> <mrow> <mi>s</mi> <mi> </mi> <mi>sin</mi> <mrow> <mo>(</mo> <mn>7</mn> <mi>&theta;</mi> <mo>+</mo> <mn>7</mn> <msub> <mi>&phi;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mo>+</mo> <mn>7</mn> <mi>&omega;</mi> <mi>cos</mi> <mrow> <mo>(</mo> <mn>7</mn> <mi>&theta;</mi> <mo>+</mo> <mn>7</mn> <msub> <mi>&phi;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> </mrow> <mrow> <mi>&omega;</mi> <mi>cos</mi> <mrow> <mo>(</mo> <msub> <mi>&phi;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mo>+</mo> <mi>s</mi> <mi> </mi> <mi>sin</mi> <mrow> <mo>(</mo> <msub> <mi>&phi;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>)</mo> <mo>&CenterDot;</mo> <mfrac> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <msup> <mi>&omega;</mi> <mn>2</mn> </msup> </mrow> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>49</mn> <msup> <mi>&omega;</mi> <mn>2</mn> </msup> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>19</mn> <mo>)</mo> </mrow> </mrow>Wherein, G1, G5, G7The fundamental wave of dead band distorted voltage, the transmission letter between 5 times and 7 subharmonic and desired voltage are represented respectively Number,Represent the fundamental wave of dead band distorted voltage5 subharmonic of dead band distorted voltage are represented,Represent dead band distorted voltage 7 subharmonic, ursThe preferable fundamental voltage of inverter output is represented, m and n are respectively dead band distorted voltage and the width of desired voltage Value, phase differences of the θ between dead band distorted voltage and desired voltage, φ0Desired voltage fundamental wave initial phase angle, ω are exported for inverter For fundamental wave angular frequency.
- 2. multiple combining inverters according to claim 1 large-sized photovoltaic grid-connected system modeling method in parallel, its feature It is：The impedance model of large-sized photovoltaic grid-connected system obtains step：S31. Fourier transformation is carried out to three-phase dead band distorted voltage；S32. take the fundamental wave of Fourier's expression formula, 5 times and 7 subharmonic to be transformed into α β axles and combine step S31 conversion knot Fruit draws single grid-connected inverters system control block figure；S33. the promise of grid-connected system is obtained according to single grid-connected inverters system control block figure and transformer with split winding equivalent inductance Lt Pause equivalent circuit；S34. the large-sized photovoltaic grid-connected system equivalent circuit that N number of combining inverter is in parallel is obtained；S35. equivalent predigesting is carried out to large-sized photovoltaic grid-connected system, obtains the Norton equivalent electricity of whole large-sized photovoltaic grid-connected system Road, further obtain the output impedance in large-sized photovoltaic power station.
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