CN107733269B - Expand the square-wave compensation control method of Cascade H bridge type photovoltaic DC-to-AC converter range of operation - Google Patents
Expand the square-wave compensation control method of Cascade H bridge type photovoltaic DC-to-AC converter range of operation Download PDFInfo
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Classifications
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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
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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- H02J3/385—
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
- H02M1/007—Plural converter units in cascade
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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Abstract
The invention discloses a kind of square-wave compensation control methods for expanding Cascade H bridge type photovoltaic DC-to-AC converter range of operation, belong to field of photovoltaic power generation.Key step is as follows: (1) carrying out independent control to the DC capacitor voltage of all H-bridge units, and obtain the active command value of grid-connected current；(2) it realizes the zero steady state error control to grid-connected current, while generating total modulation voltage of inverter and the modulation degree of all H-bridge units；(3) according to square-wave compensation strategy, the modulating wave of each H bridge module is calculated.Compared to existing disclosed document, this method can guarantee Cascade H bridge type photovoltaic combining inverter in input power there are when more serious imbalance, inverter unity power factor operates normally and DC capacitor voltage fluctuation is smaller.
Description
Technical field
The invention belongs to the photovoltaic power generation technologies of electrical engineering field, and in particular to a kind of expansion Cascade H bridge type photovoltaic is inverse
Become the square-wave compensation control method of device range of operation.
Background technique
Compared with conventional inverter, cascaded H-bridges multi-electrical level inverter low, switching frequency with grid current harmonic content
It is low, filter is small in size and the advantages that being easy to modularization, therefore obtained the concern of numerous scholars.In addition, the more level of cascaded H-bridges
The DC side of each H-bridge unit of inverter can be independently-powered by one piece of photovoltaic cell, makes its independent maximum power point tracking
(MPPT-Maximum Power Point Tracking) control is possibly realized, therefore the more level topological structures of cascaded H-bridges are outstanding
It is suitable for photovoltaic combining inverters.
Although each H-bridge unit of Cascade H bridge type photovoltaic combining inverter can be controlled by independent MPPT and be improved
The generated energy of system, if but photovoltaic cell influenced by the factors such as blocking or damaging, the output power of part photovoltaic cell can be tight
Decline again, the electric current due to flowing through each H-bridge unit it is equal and transmit power difference it is larger, the normal light of output power can be made
The corresponding H-bridge unit ovennodulation of component is lied prostrate, causes to export current capability variation or even system is unstable.
Currently, expanding the method for Cascade H bridge type photovoltaic combining inverter range of operation, to have become Cascade H bridge type photovoltaic inverse
Become the hot spot of device research.Document " L.Liming, L.Hui, X.Yaosuo and L.Wenxin, Reactive power
compensation and optimization strategy for grid-interactive cascaded
photovoltaic systems.IEEE Trans.Power Electron.,vol.30,no.1,pp.188-202,
Jan.2015. " (L.Liming, L.Hui, X.Yaosuo and L.Wenxin, cascade connection type grid-connected photovoltaic power generation system it is idle
Power compensation and its optimisation strategy, IEEE power electronics magazine, 1 phase of volume 30 in January, 2015, page 188 to page 202) pass through
Certain reactive power is compensated, can still guarantee all H-bridge units when the output power of each H-bridge unit is seriously uneven
It all will not ovennodulation.However, this method can reduce the power factor of inverter.
Document " M.Miranbeigi, and H.Iman-Eini, Hybrid modulation technique for
grid-connected cascaded photovoltaic systems.IEEE Trans.Ind.Electron.,vol.63,
No.12, pp.7843-7853, Dec.2016. " (M.Miranbeigi, and H.Iman-Eini, cascade connection type parallel network power generation
The hybrid modulation stratgy of system, IEEE industrial electronic magazine, 12 phases of volume 63 in December, 2016, page 7843 to page 7853) it mentions
A kind of low-frequency square-wave modulation and high frequency sinusoidal pulse width modulate the Balance route strategy combined out, utilize square wave maximum tune
The characteristics of system is 4/ π improves H bridge DC side voltage utilization.However, this method is each according to system running state distribution
H-bridge unit carries out charge or discharge, is not the accurate control to DC capacitor voltage, will cause DC capacitor voltage
It fluctuates larger.The fluctuation of DC voltage is so that photovoltaic module deviation maximum power point operation, reduces the average hair of photovoltaic module
Electricity.
Document " Y.Ko, M.Andresen, G.Buticchi, and M.Liserre, Power Routing for
cascaded H-bridge converters.IEEE Trans.Power Electron.,Early Access,2017.”
(Y.Ko, M.Andresen, G.Buticchi, and M.Liserre, the power path of cascaded H-bridges converter, IEEE electric power electricity
Sub- magazine is published for 2017 in advance) a kind of propose Cascade H bridge inverter triple-frequency harmonics compensation policy, it can be H-bridge unit
Modulation degree is extended to 1.155, avoids H-bridge unit ovennodulation in a certain range.Meanwhile this method also ensures system in unit
Operation and DC capacitor voltage fluctuate smaller under power factor.Compared to hybrid modulation stratgy and reactive power compensation scheme,
The comprehensive performance of triple-frequency harmonics compensation policy is more excellent.However, when system imbalance degree is heavier, the modulation of part H-bridge unit
Degree may be greater than 1.155, even if compensation triple-frequency harmonics, is not avoided that certain H-bridge unit ovennodulations still.
In conclusion the existing method for expanding Cascade H bridge type photovoltaic combining inverter range of operation is lacked there is also following
Point:
1) when the output power between a H-bridge unit is seriously uneven, although can be protected by the control of reactive power compensating strategy
All H-bridge units not ovennodulations are demonstrate,proved, but the power factor of inverter is lower, is not able to satisfy Grid-connection standards.
2) although hybrid modulation stratgy can expand the range of operation of system, DC capacitor voltage to a certain extent
It fluctuates larger, the generated energy of system can be reduced.
3) although triple-frequency harmonics compensation policy can be such that system runs under unity power factor and DC capacitor voltage
Fluctuation is smaller, but it is weaker to cope with the unbalanced ability of system.
Summary of the invention
The problem to be solved in the present invention is exactly to overcome the limitation of above-mentioned various schemes, proposes a kind of expansion Cascade H bridge type
The square-wave compensation control method of photovoltaic DC-to-AC converter range of operation, when input power imbalance between H-bridge unit, system still can
Enough unity power factor operations, and DC capacitor voltage fluctuation is smaller.Further, since can be inverter using square-wave frequency modulation
Linear modulation range be expanded to 1.27, therefore compared to existing triple-frequency harmonics compensation policy, the method can be further
The range of operation of expansion system.
In order to solve technical problem of the invention, used technical solution are as follows:
A kind of square-wave compensation control method expanding Cascade H bridge type photovoltaic DC-to-AC converter range of operation, the expansion Cascade H
Bridge type photovoltaic DC-to-AC converter includes N number of identical H-bridge unit, and the DC side of each H-bridge unit is respectively coupled one piece of photovoltaic cell,
Square-wave compensation control method of the present invention includes DC capacitor voltage control, grid-connected current controls and square-wave compensation strategy,
Steps are as follows:
Step 1, DC capacitor voltage controls
Step 1.1, the DC capacitor voltage to N number of H-bridge unit and photovoltaic cell output electric current sample respectively, obtain
The photovoltaic cell of DC capacitor voltage sampled value and corresponding N number of H-bridge unit to N number of H-bridge unit exports current sampling data,
And it is denoted as V respectivelydciAnd IPVi, i=1,2 ..., N；
Step 1.2, the DC capacitor voltage sampled value V of the N number of H-bridge unit obtained according to step 1.1dciWith N number of H bridge
The photovoltaic cell of unit exports current sampling data IPVi, maximum power point is carried out to the connected photovoltaic cell of N number of H-bridge unit respectively
Tracking, obtains the maximum power point voltage of the connected photovoltaic cell of N number of H-bridge unitThen maximum work
Rate point voltageAs H-bridge unit DC capacitor voltage instruction value；
Step 1.3, the DC capacitor voltage of N number of H-bridge unit step 1.1 obtained respectively using 100Hz trapper
Sampled value VdciIt is filtered, and the DC capacitor voltage sampled value of filtered N number of H-bridge unit is denoted as VPVi, i=1,
2,…,N；
Step 1.4, using N number of identical voltage regulator, the output power P for obtaining N number of H-bridge unit is calculated separatelyi, and
Output power summation to all H-bridge units obtains the general power P that H bridge DC side is transmitted to exchange sideT, calculating formula difference
Are as follows:
Wherein, KVPFor the proportionality coefficient of voltage regulator, KVIFor the integral coefficient of voltage regulator, s is Laplce's calculation
Son；
Step 2, grid-connected current controls
Step 2.1, network voltage and grid-connected current are sampled respectively, obtains line voltage sampled value vgWith grid-connected electricity
Flow sampled value ig；
Step 2.2, line voltage sampled value v step 2.1 obtained using digital phase-locked loopgLocking phase is carried out, electricity is obtained
Net voltage phase angle θ and grid voltage amplitude VM；
Step 2.3, grid-connected current sampled value i step 2.1 obtainedg90 degree of delay, obtains and grid-connected current sampled value ig
Orthogonal signal iQ, igAnd iQFrom two-phase static vertical coordinate system transformation to synchronous rotating frame, watt current feedback is obtained
Value IdWith reactive current value of feedback Iq, calculating formula are as follows:
Wherein, cos (θ) indicates that the cosine value of electric network voltage phase angle θ, sin (θ) are indicating electric network voltage phase angle θ just
String value；
Step 2.4, if the referenced reactive current value of inverterIt is given as 0, active current command valueCalculating formula such as
Under:
Step 2.5, the active tune of inverter is calculated by watt current adjuster and reactive current adjuster respectively
Voltage U processeddWith idle modulation voltage Uq, calculating formula is respectively as follows:
Wherein, KiPFor the proportionality coefficient of current regulator, KiIFor the integral coefficient of current regulator；
Step 2.6, total modulation voltage amplitude V of inverter is calculatedr, total modulation voltage and network voltage angle thetarWith N number of H
The modulation degree S of bridge uniti, i=1,2 ..., N, calculating formula is distinguished as follows:
Wherein, arctan (Uq/Ud) indicate Uq/UdArc-tangent value；
Step 3, square-wave compensation strategy
By the 1st, 2 ..., the modulation degree of x H-bridge unit is set between 1~1.27, and referred to as ovennodulation H bridge list
Member, (x+1)th ..., the modulation degree of N number of H-bridge unit are set less than 1, referred to as non-ovennodulation H-bridge unit, x < N；
The square-wave compensation strategy the following steps are included:
Step 3.1, it is square wave the modulating wave compensation of ovennodulation H-bridge unit, and guarantees H-bridge unit modulating wave after compensating
Fundametal compoment is equal with before compensation, specifically, i-th of ovennodulation H-bridge unit modulating wave miCalculating formula are as follows:
Wherein, π is pi；
Step 3.2, total harmonic voltage v that ovennodulation H-bridge unit is compensated is calculatedHTP, calculating formula are as follows:
Step 3.3, to all non-ovennodulation H-bridge unit compensation and vHTPThe harmonic voltage v of reverse phaseHTN, calculating formula are as follows:
Step 3.4, harmonic voltage vHTNIt is assigned to non-ovennodulation H-bridge unit, the distribution coefficient k of j-th of H-bridge unitjMeter
It calculates as follows:
Step 3.5, the modulating wave m of j-th of H-bridge unit is calculatedj, calculating formula is as follows:
The beneficial effect of the present invention compared with the prior art is:
1, when the input power imbalance of H-bridge unit, system can unity power factor operate normally, and DC side electricity
It is smaller to hold voltage fluctuation.
2, the triple-frequency harmonics compensation policy referred to compared to existing literature, can further expansion Cascade H bridge type photovoltaic it is inverse
Become the range of operation of device.
Detailed description of the invention
Fig. 1 is the single-phase Cascade H bridge type photovoltaic combining inverter main circuit topological structure that the present invention is implemented.
Fig. 2 is the single-phase Cascade H bridge type photovoltaic combining inverter control block diagram that the present invention is implemented.
Fig. 3 is the flow chart of square-wave compensation strategy of the present invention.
Fig. 4 is that H-bridge unit input power is uneven, using line voltage sampled value v when triple-frequency harmonics compensation policygSimultaneously
Net current sampling data igWaveform.
Fig. 5 is that H-bridge unit input power is uneven, using the modulating wave m of first H-bridge unit when square-wave compensation strategy1、
The DC capacitor voltage sampled value V of first H-bridge unitdc1With DC capacitor voltage instruction valueAnd network voltage
Sampled value vgWith grid-connected current sampled value igWaveform.
Specific embodiment
In order to make the objectives, technical solutions, and advantages of the present invention clearer, with reference to the accompanying drawings and embodiments, right
The present invention, which is done, further clearly and completely to be described.
Fig. 1 is the single-phase Cascade H bridge type photovoltaic combining inverter main circuit topological structure that the present invention is implemented, including containing N number of
Identical H-bridge unit, each H-bridge unit are made of four full-controlled switch devices.Each electrolysis in parallel in each H bridge front end
Capacitor Ci(i=1,2 ..., N), each electrolytic capacitor respectively with one piece of photovoltaic cell PVi(i=1,2 ..., N) connection.All H bridges
Exchange side output be serially connected after, pass through filter inductance L1And L2It is connect with power grid, wherein R1And R2Respectively filter inductance L1
And L2Equivalent resistance.V in figuredciAnd IPVi(i=1,2 ..., N) respectively indicates i-th of H-bridge unit DC capacitor voltage and adopts
Sample value and corresponding photovoltaic module export current sampling data, vgAnd igRespectively indicate line voltage sampled value and grid-connected current sampling
Value.In this implementation, the capacitor C of each H-bridge unit prime parallel connectioniIt is 27.2mF (i=1,2 ..., N), filter inductance L1=L2
=0.75mH, equivalent resistance R1=R2=0.005 Ω, the amplitude and frequency of network voltage are respectively 90V and 50Hz.
Fig. 2 is the single-phase Cascade H bridge type photovoltaic combining inverter control block diagram that the present invention is implemented, it is by a master controller
It is formed with N number of H bridge controller.Master controller realizes grid-connected current control and according to each H bridge mould of square-wave compensation policy calculation
The modulating wave m of blocki(i=1,2 ..., N).Maximum power point tracking (MPPT-Maximum of H bridge controller realization photovoltaic module
Power Point Tracking) control, H-bridge unit DC capacitor voltage control and according to master controller calculate H bridge list
The modulating wave of member generates the driving signal of four full-controlled switch devices of H-bridge unit.
Fig. 3 is the flow chart that the present invention implements square wave compensation policy, first according to the square-wave compensation strategy proposed mistake
The modulating wave compensation for modulating H-bridge unit is square wave, for the normal operation of Guarantee control system, the fundamental wave of modulating wave point after compensation
Amount should be equal with the preceding fundametal compoment of modulating wave is compensated.Then, total harmonic voltage v that ovennodulation H-bridge unit is compensated is calculatedHTP,
The harmonic wave compensated is free of in order to make the exchange side of Cascade H bridge type photovoltaic DC-to-AC converter export total voltage, is needed to non-ovennodulation H
Bridge unit compensation and vHTPThe harmonic voltage v of reverse phaseHTN.Finally, calculating the distribution coefficient and modulating wave of non-ovennodulation H-bridge unit.
Referring to figure 1, figure 2 and figure 3, implementation process of the invention is as follows:
Step 1, DC capacitor voltage controls
Step 1.1, the DC capacitor voltage to N number of H-bridge unit and photovoltaic cell output electric current sample respectively, obtain
The photovoltaic cell of DC capacitor voltage sampled value and corresponding N number of H-bridge unit to N number of H-bridge unit exports current sampling data,
And it is denoted as V respectivelydciAnd IPVi, i=1,2 ..., N；
Step 1.2, the DC capacitor voltage sampled value V of the N number of H-bridge unit obtained according to step 1.1dciWith N number of H bridge
The photovoltaic cell of unit exports current sampling data IPVi, maximum power point is carried out to the connected photovoltaic cell of N number of H-bridge unit respectively
Tracking, obtains the maximum power point voltage of the connected photovoltaic cell of N number of H-bridge unitThen maximum work
Rate point voltageAs H-bridge unit DC capacitor voltage instruction value；
Step 1.3, the DC capacitor voltage of N number of H-bridge unit step 1.1 obtained respectively using 100Hz trapper
Sampled value VdciIt is filtered, and the DC capacitor voltage sampled value of filtered N number of H-bridge unit is denoted as VPVi, i=1,
2,…,N；
Step 1.4, using N number of identical voltage regulator, the output power P for obtaining N number of H-bridge unit is calculated separatelyi, and
Output power summation to all H-bridge units obtains the general power P that H bridge DC side is transmitted to exchange sideT, calculating formula difference
Are as follows:
Wherein, KVPFor the proportionality coefficient of voltage regulator, KVIFor the integral coefficient of voltage regulator, s is Laplce's calculation
Son.Voltage regulator Proportional coefficient KVPWith voltage regulator integral coefficient KVIIt is designed according to conventional gird-connected inverter, this reality
Shi Zhong, KVP=8, KVI=150.
Step 2, grid-connected current controls
Step 2.1, network voltage and grid-connected current are sampled respectively, obtains line voltage sampled value vgWith grid-connected electricity
Flow sampled value ig；
Step 2.2, line voltage sampled value v step 2.1 obtained using digital phase-locked loopgLocking phase is carried out, electricity is obtained
Net voltage phase angle θ and grid voltage amplitude VM；
Step 2.3, grid-connected current sampled value i step 2.1 obtainedg90 degree of delay, obtains and grid-connected current sampled value ig
Orthogonal signal iQ, igAnd iQFrom two-phase static vertical coordinate system transformation to synchronous rotating frame, watt current feedback is obtained
Value IdWith reactive current value of feedback Iq, calculating formula are as follows:
Wherein, cos (θ) indicates that the cosine value of electric network voltage phase angle θ, sin (θ) are indicating electric network voltage phase angle θ just
String value；
Step 2.4, if the referenced reactive current value of inverterIt is given as 0, active current command valueCalculating formula such as
Under:
Step 2.5, the active tune of inverter is calculated by watt current adjuster and reactive current adjuster respectively
Voltage U processeddWith idle modulation voltage Uq, calculating formula is respectively as follows:
Wherein, KiPFor the proportionality coefficient of current regulator, KiIFor the integral coefficient of current regulator, s is Laplce's calculation
Son.Current regulator Proportional coefficient KiPWith current regulator integral coefficient KiIIt is designed according to conventional gird-connected inverter, this reality
Shi Zhong, KiP=1.5, KiI=50.
Step 2.6, total modulation voltage amplitude V of inverter is calculatedr, total modulation voltage and network voltage angle thetarWith N number of H
The modulation degree S of bridge uniti, i=1,2 ..., N, calculating formula is distinguished as follows:
Wherein, arctan (Uq/Ud) indicate Uq/UdArc-tangent value.
Step 3, square-wave compensation strategy
By the 1st, 2 ..., the modulation degree of x H-bridge unit is set between 1~1.27, and referred to as ovennodulation H bridge list
Member, (x+1)th ..., the modulation degree of N number of H-bridge unit are set less than 1, referred to as non-ovennodulation H-bridge unit, x < N；
The square-wave compensation strategy the following steps are included:
Step 3.1, it is square wave the modulating wave compensation of ovennodulation H-bridge unit, and guarantees H-bridge unit modulating wave after compensating
Fundametal compoment is equal with before compensation, specifically, i-th of ovennodulation H-bridge unit modulating wave miCalculating formula are as follows:
Wherein, π is pi；
Step 3.2, total harmonic voltage v that ovennodulation H-bridge unit is compensated is calculatedHTP, calculating formula are as follows:
Step 3.3, to all non-ovennodulation H-bridge unit compensation and vHTPThe harmonic voltage v of reverse phaseHTN, calculating formula are as follows:
Step 3.4, vHTNIt is assigned to non-ovennodulation H-bridge unit, the distribution coefficient k of j-th of H-bridge unitjIt calculates as follows:
Step 3.5, the modulating wave m of j-th of H-bridge unit is calculatedj, calculating formula is as follows:
Fig. 4 is that the intensity of illumination of four H-bridge unit prime photovoltaic cells is respectively 1000W/m2、1000W/m2、350W/m2
And 350W/m2, temperature is 25 DEG C, using line voltage sampled value v when triple-frequency harmonics compensation policygWith grid-connected current sampled value
igWaveform diagram.In this implementation, the model JAP6 60-260/3BB of selected photovoltaic module, when intensity of illumination is 1000W/
m2, when temperature is 25 DEG C, peak power output 260W, maximum power point voltage 30.63V.Obviously, photovoltaic module is defeated
There are serious imbalances for power out, can toning since the input power of first H-bridge unit and second H-bridge unit is larger
System.However, since regulating power is limited, grid-connected current waveform is the sine wave of distortion when using triple-frequency harmonics compensation policy, and
Harmonic content is larger.
Fig. 5 is the modulating wave of first H-bridge unit when using square-wave compensation strategy proposed by the invention under equal conditions
m1, first H-bridge unit DC capacitor voltage sampled value Vdc1With DC capacitor voltage instruction valueAnd power grid electricity
Press sampled value vgWith grid-connected current sampled value igWaveform.As can be seen that the modulating wave of first H-bridge unit is compensated for as square wave,
Its amplitude is less than 1；DC capacitor voltage sampled value Vdc1DC capacitor voltage instruction value can be accurately trackedFluctuation
Peak-to-peak value be about 0.7V；Inverter can be in stable operation under unity power factor, and grid-connected current sampled value igPerformance
Preferably.
Claims (1)
1. a kind of square-wave compensation control method for expanding Cascade H bridge type photovoltaic DC-to-AC converter range of operation, the Cascade H bridge type photovoltaic
Inverter includes N number of identical H-bridge unit, and the DC side of each H-bridge unit is respectively coupled one piece of photovoltaic cell, and feature exists
In the square-wave compensation control method includes DC capacitor voltage control, grid-connected current control and square-wave compensation strategy, step
It is as follows:
Step 1, DC capacitor voltage controls
Step 1.1, the DC capacitor voltage to N number of H-bridge unit and photovoltaic cell output electric current sample respectively, obtain N
The photovoltaic cell of the DC capacitor voltage sampled value of a H-bridge unit and corresponding N number of H-bridge unit exports current sampling data, and
It is denoted as V respectivelydciAnd IPVi, i=1,2 ..., N；
Step 1.2, the DC capacitor voltage sampled value V of the N number of H-bridge unit obtained according to step 1.1dciWith N number of H-bridge unit
Photovoltaic cell export current sampling data IPVi, maximum power point tracking is carried out to the connected photovoltaic cell of N number of H-bridge unit respectively,
Obtain the maximum power point voltage of the connected photovoltaic cell of N number of H-bridge unitThen maximum power point electricity
PressureAs H-bridge unit DC capacitor voltage instruction value；
Step 1.3, the DC capacitor voltage of the N number of H-bridge unit obtained respectively to step 1.1 using 100Hz trapper is sampled
Value VdciIt is filtered, and the DC capacitor voltage sampled value of filtered N number of H-bridge unit is denoted as VPVi, i=1,2 ...,
N；
Step 1.4, using N number of identical voltage regulator, the output power P for obtaining N number of H-bridge unit is calculated separatelyi, and to institute
There is the output power of H-bridge unit to sum, obtains the general power P that H bridge DC side is transmitted to exchange sideT, calculating formula is respectively as follows:
Wherein, KVPFor the proportionality coefficient of voltage regulator, KVIFor the integral coefficient of voltage regulator, s is Laplace operator；
Step 2, grid-connected current controls
Step 2.1, network voltage and grid-connected current are sampled respectively, obtains line voltage sampled value vgIt is adopted with grid-connected current
Sample value ig；
Step 2.2, line voltage sampled value v step 2.1 obtained using digital phase-locked loopgLocking phase is carried out, network voltage is obtained
Phase angle θ and grid voltage amplitude VM；
Step 2.3, grid-connected current sampled value i step 2.1 obtainedg90 degree of delay, obtains and grid-connected current sampled value igIt is orthogonal
Signal iQ, igAnd iQFrom two-phase static vertical coordinate system transformation to synchronous rotating frame, watt current value of feedback I is obtainedd
With reactive current value of feedback Iq, calculating formula are as follows:
Wherein, cos (θ) indicates that the cosine value of electric network voltage phase angle θ, sin (θ) indicate the sine value of electric network voltage phase angle θ；
Step 2.4, if the referenced reactive current value of inverterIt is given as 0, active current command valueCalculating formula it is as follows:
Step 2.5, the active modulation electricity of inverter is calculated by watt current adjuster and reactive current adjuster respectively
Press UdWith idle modulation voltage Uq, calculating formula is respectively as follows:
Wherein, KiPFor the proportionality coefficient of current regulator, KiIFor the integral coefficient of current regulator；
Step 2.6, total modulation voltage amplitude V of inverter is calculatedr, total modulation voltage and network voltage angle thetarWith N number of H bridge list
The modulation degree S of memberi, i=1,2 ..., N, calculating formula is distinguished as follows:
Wherein, arctan (Uq/Ud) indicate Uq/UdArc-tangent value；
Step 3, square-wave compensation strategy
By the 1st, 2 ..., the modulation degree of x H-bridge unit is set between 1~1.27, and referred to as ovennodulation H-bridge unit, the
X+1 ..., the modulation degree of N number of H-bridge unit are set less than 1, referred to as non-ovennodulation H-bridge unit, x < N；
The square-wave compensation strategy the following steps are included:
Step 3.1, it is square wave the modulating wave compensation of ovennodulation H-bridge unit, and guarantees the fundamental wave of H-bridge unit modulating wave after compensation
Component is equal with before compensation, specifically, i-th of ovennodulation H-bridge unit modulating wave miCalculating formula are as follows:
Wherein, π is pi；
Step 3.2, total harmonic voltage v that ovennodulation H-bridge unit is compensated is calculatedHTP, calculating formula are as follows:
Step 3.3, to all non-ovennodulation H-bridge unit compensation and vHTPThe harmonic voltage v of reverse phaseHTN, calculating formula are as follows:
Step 3.4, harmonic voltage vHTNIt is assigned to non-ovennodulation H-bridge unit, the distribution coefficient k of j-th of H-bridge unitjIt calculates such as
Under:
Step 3.5, the modulating wave m of j-th of H-bridge unit is calculatedj, calculating formula is as follows:
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