CN110311406A - A kind of control method expanding cascaded H-bridges photovoltaic DC-to-AC converter range of operation - Google Patents
A kind of control method expanding cascaded H-bridges 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
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/01—Arrangements for reducing harmonics or ripples
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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
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
- H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
- H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
- H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
- H02J3/1857—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters wherein such bridge converter is a multilevel converter
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- H02J3/385—
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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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- 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
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/20—Active power filtering [APF]
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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
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
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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
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/40—Arrangements for reducing harmonics
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- Inverter Devices (AREA)
Abstract
The invention discloses a kind of control methods for expanding cascaded H-bridges photovoltaic DC-to-AC converter range of operation, belong to field of photovoltaic power generation.Key step is as follows: (1) controlling the DC voltage of all H-bridge units, obtain watt current instruction；(2) the reverse phase third harmonic voltage for the fundamental wave of power network current being controlled, and the triple-frequency harmonics of power network current being controlled, and compensated needed for obtaining；(3) modulation degree of H-bridge unit is calculated, and compensates triple-frequency harmonics to the H-bridge unit of ovennodulation, obtains the modulating wave of ovennodulation H-bridge unit；(4) according to the control method proposed, reverse phase third harmonic voltage is assigned to the H-bridge unit of non-ovennodulation, obtains the modulating wave of non-ovennodulation H-bridge unit.Compared to existing disclosed document, this method can guarantee Cascade H bridge type photovoltaic combining inverter, and in input power, there are when more serious imbalance, inverter unity power factor is operated normally, the smaller and power network current triple-frequency harmonics content of DC capacitor voltage fluctuation is lower.
Description
Technical field
The invention belongs to the photovoltaic power generation technologies of electrical engineering field, and in particular to a kind of to expand single-phase cascaded H-bridges photovoltaic
The control method of invertor operation range.
Background technique
Compared with traditional inverter, Cascade H bridge type multi-electrical level inverter is low with grid current harmonic content, switchs frequency
Rate is low, filter is small in size and the advantages that being easy to modularization, therefore has obtained the concern of numerous scholars.In addition, how electric cascaded H-bridges are
The DC side of each H-bridge unit of flat inverter can be independently-powered by one piece of photovoltaic cell, chases after its independent maximum power point
Track (MPPT-Maximum Power Point Tracking) control is possibly realized, therefore the more level topological structures of cascaded H-bridges
It is particularly suitable for photovoltaic combining inverter.
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, the range of operation for how expanding Cascade H bridge type inverter has become the research of Cascade H bridge type photovoltaic DC-to-AC converter
Hot spot.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, the reactive power compensation of cascade connection type grid-connected photovoltaic power generation system and
Its optimisation strategy, IEEE power electronics magazine, 1 phase of volume 30 in January, 2015, page 188 to page 202) certain by compensation
Reactive power can still guarantee that all H bridge modules all will not toning when the output power of each H bridge module is seriously uneven
System.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 module 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) propose a kind of triple-frequency harmonics compensation policy, the modulation degree of H-bridge unit can be extended to
1.155, H-bridge unit ovennodulation is avoided in a certain range.Meanwhile this method also ensures that system is transported under unity power factor
Row and DC capacitor voltage fluctuate smaller.Compared to hybrid modulation stratgy and reactive power compensation scheme, triple-frequency harmonics compensation
The comprehensive performance of strategy is more excellent.However, the reverse phase triple-frequency harmonics compensation policy that the document is proposed is a kind of calculating side of open loop
Method does not ensure that power network current without triple-frequency harmonics ingredient.Secondly, the document not yet refers to reverse phase triple-frequency harmonics in non-toning
The assignment problem of molding block has certain application limitation.
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 of each H bridge module is seriously uneven, although the control of reactive power compensating strategy can guarantee institute
There are H bridge module not ovennodulations, but system power factor is lower, is not able to satisfy Grid-connection standards.
2), although hybrid modulation stratgy can expand the range of operation of system, DC bus capacitor electricity to a certain extent
Pressure fluctuation is larger, can reduce the generated energy of system.
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 the compensation of reverse phase triple-frequency harmonics is open-loop compensation, it cannot be guaranteed that power network current is free of triple-frequency harmonics ingredient.This
Outside, reverse phase triple-frequency harmonics is not yet referred in the assignment problem of non-ovennodulation intermodule.
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 cascaded H-bridges light
The control method of invertor operation range is lied prostrate, when input power imbalance between H-bridge unit, system still being capable of unit power
Factor operation, and DC capacitor voltage fluctuation is smaller.In addition, proposing a kind of reverse phase triple-frequency harmonics based on quasi resonant control
Compensation policy, the third-harmonic component that can be effectively reduced in power network current.
In order to solve technical problem of the invention, used technical solution are as follows:
A kind of control method expanding cascaded H-bridges photovoltaic DC-to-AC converter range of operation, the cascaded H-bridges photovoltaic DC-to-AC converter category
In single-phase photovoltaic inverter, including N number of identical H-bridge unit, N are positive integer, and each H-bridge unit is by four full-controlled switch
Device composition, each each electrolytic capacitor in parallel in H-bridge unit front end, each electrolytic capacitor respectively with one piece of photovoltaic module simultaneously
Connection, which is characterized in that the control method includes the control of H-bridge unit DC capacitor voltage, grid-connected current control, H bridge list
The modulation degree and modulating wave of member calculate, and steps are as follows:
Step 1, H-bridge unit DC capacitor voltage controls
Step 1.1, the output electric current of the DC capacitor voltage of N number of H-bridge unit and corresponding photovoltaic module is carried out respectively
Sampling obtains the output electricity of the DC capacitor voltage sampled value of N number of H-bridge unit and the photovoltaic module of corresponding N number of H-bridge unit
Sampled value is flowed, will and be 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 output current sampling data I of the photovoltaic module of unitPVi, maximum power is carried out to the connected photovoltaic module of N number of H-bridge unit respectively
Point tracking obtains the maximum power point voltage of the connected photovoltaic module of N number of H-bridge unitThen maximum power point voltageAs the instruction value of H-bridge unit DC capacitor voltage, i=1,2 ..., N；
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
The phase angle θ of net voltage, angular frequency0With 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
The amplitude U of voltage processeddWith the amplitude U of idle modulation voltageq, calculating formula is respectively as follows:
Wherein, KiPFor the proportionality coefficient of current regulator, KiIFor the integral coefficient of current regulator；
Step 2.6, the quasi resonant control for reusing a three times electrical network angular frequency, grid-connected current igControl is 0, three
The output of the quasi resonant control of times electrical network angular frequency is the third harmonic voltage v that system needs to compensatePR3, calculating formula are as follows:
Wherein, ωcFor the cutoff frequency of the quasi resonant control of three times electrical network angular frequency, krFor three times electrical network angular frequency
The proportionality coefficient of quasi resonant control；
Step 3, the modulation degree of H-bridge unit and modulating wave calculate
N number of H-bridge unit is divided into following two categories: by the 1,2nd ..., the modulation degree setting of x H-bridge unit between 1~
Between 1.155, and referred to as ovennodulation H-bridge unit；The modulation degree of (x+1)th ..., N number of H-bridge unit is set less than 1, and is referred to as
For non-ovennodulation H-bridge unit, x is positive integer, and x < N；
Step 3.1, total modulation voltage amplitude V of inverter is calculatedr, total modulation voltage and network voltage angle thetar, N number of H bridge
The modulation degree S of uniti, i=1,2 ..., N, calculating formula is distinguished as follows:
Wherein, arctan (Uq/Ud) indicate Uq/UdArc-tangent value；
Step 3.2, triple-frequency harmonics is compensated to the modulating wave of ovennodulation H-bridge unit, specifically, x ovennodulation H is calculated
The modulating wave m of bridge unitAi, i=1,2 ..., x, calculating formula is as follows:
Step 3.3, the third harmonic voltage v for system being needed to compensatePR3It is assigned to non-ovennodulation H-bridge unit, specifically,
The distribution coefficient q of K non-ovennodulation H-bridge units is calculatedi, i=x+1, x+2 ..., N, k=N-x, calculating formula be as follows:
Step 3.4, the modulating wave m of k non-ovennodulation H-bridge units is calculatedBi, i=x+1, x+2 ..., N are calculated
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 little to hold voltage fluctuation.
2, using the reverse phase triple-frequency harmonics compensation policy of closed loop, the triple-frequency harmonics point of power network current can be effectively reduced
Amount.
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 control strategy of the present invention.
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 PViConnection, i=1,2 ..., N.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 IPViRespectively indicate i-th of H-bridge unit DC capacitor voltage sampled value and corresponding light
It lies prostrate component and exports current sampling data, i=1,2 ..., N；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 100V 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 calculates the modulating wave of each H bridge module.H bridge control
Device processed realizes maximum power point tracking (MPPT-Maximum Power Point Tracking) control of photovoltaic module, H bridge
The modulating wave of the control of unit DC capacitor voltage and the H-bridge unit calculated according to master controller generates corresponding H-bridge unit
The driving signal of four full-controlled switch devices.
Fig. 3 is the flow chart for the control strategy that the present invention is implemented.Firstly, the DC voltage to all H-bridge units carries out
Control obtains watt current instruction.Secondly, the fundamental wave to power network current controls, and to the triple-frequency harmonics of power network current
The reverse phase third harmonic voltage v for being controlled, and being compensated needed for obtainingPR3.Then, the modulation degree of H-bridge unit is calculated, and was given
The H-bridge unit of modulation compensates triple-frequency harmonics, obtains the modulating wave of ovennodulation H-bridge unit.Finally, according to the controlling party proposed
Method, reverse phase third harmonic voltage vPR3It is assigned to the H-bridge unit of non-ovennodulation, obtains the 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, H-bridge unit DC capacitor voltage controls
Step 1.1, the output electric current of the DC capacitor voltage of N number of H-bridge unit and corresponding photovoltaic module is carried out respectively
Sampling obtains the output electricity of the DC capacitor voltage sampled value of N number of H-bridge unit and the photovoltaic module of corresponding N number of H-bridge unit
Sampled value is flowed, will and be 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 output current sampling data I of the photovoltaic module of unitPVi, maximum power is carried out to the connected photovoltaic module of N number of H-bridge unit respectively
Point tracking obtains the maximum power point voltage of the connected photovoltaic module of N number of H-bridge unitThen maximum power point voltageAs the instruction value of H-bridge unit DC capacitor voltage, i=1,2 ..., N；
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
The phase angle θ of net voltage, angular frequency0With 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
The amplitude U of voltage processeddWith the amplitude U of idle modulation voltageq, 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, the quasi resonant control for reusing a three times electrical network angular frequency, grid-connected current igControl is 0, three
The output of the quasi resonant control of times electrical network angular frequency is the third harmonic voltage v that system needs to compensatePR3, calculating formula are as follows:
Wherein, ωcFor the cutoff frequency of the quasi resonant control of three times electrical network angular frequency, krFor three times electrical network angular frequency
The proportionality coefficient of quasi resonant control；ωcAnd krIt is designed according to the design method of conventional quasi resonant control, in this implementation,
ωc=3.14, kr=80.
Step 3, the modulation degree of H-bridge unit and modulating wave calculate
N number of H-bridge unit is divided into following two categories: by the 1,2nd ..., the modulation degree setting of x H-bridge unit between 1~
Between 1.155, and referred to as ovennodulation H-bridge unit；The modulation degree of (x+1)th ..., N number of H-bridge unit is set less than 1, and is referred to as
For non-ovennodulation H-bridge unit, x is positive integer, and x < N；
Step 3.1, total modulation voltage amplitude V of inverter is calculatedr, total modulation voltage and network voltage angle thetar, N number of H bridge
The modulation degree S of uniti, i=1,2 ..., N, calculating formula is distinguished as follows:
Wherein, arctan (Uq/Ud) indicate Uq/UdArc-tangent value；
Step 3.2, triple-frequency harmonics is compensated to the modulating wave of ovennodulation H-bridge unit, specifically, x ovennodulation H is calculated
The modulating wave m of bridge unitAi, i=1,2 ..., x, calculating formula is as follows:
Step 3.3, the third harmonic voltage v for system being needed to compensatePR3It is assigned to non-ovennodulation H-bridge unit, specifically,
The distribution coefficient q of K non-ovennodulation H-bridge units is calculatedi, i=x+1, x+2 ..., N, k=N-x, calculating formula be as follows:
Step 3.4, the modulating wave m of k non-ovennodulation H-bridge units is calculatedBi, i=x+1, x+2 ..., N are calculated
Formula is as follows:
After the modulating wave for calculating all H-bridge units using above step, using phase-shifting carrier wave sine wave pulse width tune
The switching drive signal of the available all H-bridge units of system strategy.The phase-shifting carrier wave sine wave pulse width modulated strategy
Refer to the generally used modulation strategy of cascaded H-bridges converter, this is in cascaded H-bridges converter using more and more mature
Technology.There is very much document to describe phase-shifting carrier wave sine wave pulse width modulated in detail, such as Zhou Jinghua and Chen Yaai 2013
84-88 of the year in the monograph " high-performance cascade multi-level converter principle and application " that China Machine Press publishes
Page.
Claims (1)
1. a kind of control method for expanding cascaded H-bridges photovoltaic DC-to-AC converter range of operation, the cascaded H-bridges photovoltaic DC-to-AC converter belong to
Single-phase photovoltaic inverter, including N number of identical H-bridge unit, N are positive integer, each H-bridge unit is by four full-controlled switch devices
Part composition, each each electrolytic capacitor in parallel in H-bridge unit front end, each electrolytic capacitor respectively with one piece of photovoltaic module simultaneously
Connection, which is characterized in that the control method includes the control of H-bridge unit DC capacitor voltage, grid-connected current control, H bridge list
The modulation degree and modulating wave of member calculate, and steps are as follows:
Step 1, H-bridge unit DC capacitor voltage controls
Step 1.1, the output electric current of the DC capacitor voltage of N number of H-bridge unit and corresponding photovoltaic module is sampled respectively,
The output electric current for obtaining the DC capacitor voltage sampled value of N number of H-bridge unit and the photovoltaic module of corresponding N number of H-bridge unit is adopted
Sample value will and be 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 module output current sampling data IPVi, maximum power point is carried out to the connected photovoltaic module of N number of H-bridge unit respectively and is chased after
Track obtains the maximum power point voltage of the connected photovoltaic module of N number of H-bridge unitThen maximum power point voltageMake
For the instruction value of H-bridge unit DC capacitor voltage, i=1,2 ..., N；
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, angular frequency0With 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:
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
The amplitude U of pressuredWith the amplitude U of idle modulation voltageq, calculating formula is respectively as follows:
Wherein, KiPFor the proportionality coefficient of current regulator, KiIFor the integral coefficient of current regulator；
Step 2.6, the quasi resonant control for reusing a three times electrical network angular frequency, grid-connected current igControl is 0, three times electricity
The output of the quasi resonant control of net angular frequency is the third harmonic voltage v that system needs to compensatePR3, calculating formula are as follows:
Wherein, ωcFor the cutoff frequency of the quasi resonant control of three times electrical network angular frequency, krIt is humorous for the standard of three times electrical network angular frequency
The proportionality coefficient of vibration controller；
Step 3, the modulation degree of H-bridge unit and modulating wave calculate
N number of H-bridge unit is divided into following two categories: by the 1,2nd ..., the modulation degree setting of x H-bridge unit between 1~1.155 it
Between, and referred to as ovennodulation H-bridge unit；The modulation degree of (x+1)th ..., N number of H-bridge unit is set less than 1, and referred to as non-mistake
H-bridge unit is modulated, x is positive integer, and x < N；
Step 3.1, total modulation voltage amplitude V of inverter is calculatedr, total modulation voltage and network voltage angle thetar, N number of H-bridge unit
Modulation degree Si, i=1,2 ..., N, calculating formula is distinguished as follows:
Wherein, arctan (Uq/Ud) indicate Uq/UdArc-tangent value；
Step 3.2, triple-frequency harmonics is compensated to the modulating wave of ovennodulation H-bridge unit, specifically, x ovennodulation H bridge list is calculated
The modulating wave m of memberAi, i=1,2 ..., x, calculating formula is as follows:
Step 3.3, the third harmonic voltage v for system being needed to compensatePR3It is assigned to non-ovennodulation H-bridge unit, specifically, calculating
Obtain the distribution coefficient q of K non-ovennodulation H-bridge unitsi, i=x+1, x+2 ..., N, k=N-x, calculating formula be as follows:
Step 3.4, the modulating wave m of k non-ovennodulation H-bridge units is calculatedBi, i=x+1, x+2 ..., N, calculating formula is such as
Under:
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| CN112909993B (en) * | 2021-01-21 | 2022-07-05 | 山东大学 | Three-phase current unbalance compensation method for medium-voltage photovoltaic power generation system |
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| CN114172402A (en) * | 2021-12-03 | 2022-03-11 | 合肥工业大学 | Harmonic compensation control strategy for expanding operation range of cascaded H-bridge photovoltaic inverter |
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| CN114825442B (en) * | 2022-05-09 | 2024-03-26 | 合肥工业大学 | Single-phase cascade H-bridge photovoltaic inverter control strategy based on low-frequency harmonic compensation |
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