CN108847688A - A kind of space vector modulating method of single-phase cascade type photovoltaic DC-to-AC converter - Google Patents
A kind of space vector modulating method of single-phase cascade type photovoltaic DC-to-AC converter Download PDFInfo
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- H02J3/383—
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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
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
- H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
- H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
- H02M7/53875—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output
- H02M7/53876—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output based on synthesising a desired voltage vector via the selection of appropriate fundamental voltage vectors, and corresponding dwelling times
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/539—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency
- H02M7/5395—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency by pulse-width modulation
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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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- Inverter Devices (AREA)
Abstract
The present invention relates to photovoltaic DC-to-AC converter modulation techniques, more particularly to a kind of space vector modulating method of single-phase cascade type photovoltaic DC-to-AC converter, on the basis of Traditional Space vector modulation method, the difference of the DC voltage instruction value provided according to each unit DC voltage instantaneous value and its MPPT module determines that the unit DC side should charge, electric discharge or DC voltage remain unchanged, in the one-dimensional space of single-phase inverter output vector, an output vector with the most consistent vector of each unit charge/discharge demand as next switch periods is respectively selected from the two side areas of controller output voltage instruction value according to the instantaneous direction of grid-connected inverters electric current, duty ratio is calculated further according to controller output voltage instruction value and level value corresponding to two output vectors.Modified space vector modulation method is applied to photovoltaic generating system by the modulator approach, and instead of the part of unit DC voltage Balance route in controller algorithm, simplified control device structure is conducive to improve stability of control system.
Description
Technical field
The invention belongs to photovoltaic DC-to-AC converter modulation technique field more particularly to a kind of skies of single-phase cascade type photovoltaic DC-to-AC converter
Between vector modulation method.
Background technique
Due to energy and environmental problem, effect of the photovoltaic generating system in using energy source is more and more important.It is sent out in photovoltaic
In electric system, photovoltaic DC-to-AC converter is that a kind of direct current by photovoltaic cell output is converted into the important equipment of required alternating current.
There are many topological structures for the circuit of photovoltaic DC-to-AC converter, and one of structure is cascade connection type photovoltaic DC-to-AC converter, i.e., each photovoltaic cell
String (or component) is connect with the DC terminal of a single-phase inverter, and the ac output end of all single-phase inverters is successively gone here and there again
Connection constitutes high-voltage alternating output.Such photovoltaic DC-to-AC converter can directly to grid transmission or power to the load, without
It is boosted using AC transformer.Each photovoltaic cell and the single-phase inverter being attached thereto are referred to as a unit.
The generated output size of each photovoltaic cell string (component) by its DC voltage control, and with intensity of illumination,
The factors such as temperature, photovoltaic cell surface block, the dispersibility of photovoltaic cell parameter are closely related.If the thus photovoltaic of all units
Battery strings (component) all work in the maximum power point of its own, it will cause the DC voltage of each unit different.Conversely, if each
Unit DC voltage is controlled as the same numerical value, is not work in maximum power point there will be certain photovoltaic cells, reduces
Whole generating efficiency.Therefore, in order to improve the generating efficiency of photovoltaic cell, it should use independent maximum work to each unit
Rate point tracks (MPPT) technology, the DC voltage instruction value for making its DC voltage that its MPPT be followed to export, so that work is respective
Maximum power point so that system generating efficiency reaches highest.Usually such control is in the controller by photovoltaic DC-to-AC converter
What specific control algolithm was realized.
In addition to control algolithm, the controller of cascade connection type photovoltaic DC-to-AC converter will also use suitable modulator approach by control algolithm
Output order value be changed into the switching signal of each unit.The modulator approach that cascaded inverter generallys use has phase-shifting carrier wave
Modulate (PS-PWM), the hybrid modulation (H-PWM) of " step modulation+carrier modulation ", carrier wave shifting width modulation (LS-PWM).These are adjusted
Method processed be premised on each unit dc-voltage balance, but due in practical application each unit photovoltaic cell by extraneous each
Kind factor influences, and DC voltage can shift, final to influence photovoltaic DC-to-AC converter output voltage waveforms quality.Also there are certain tune
Method processed is adapted to the slightly unbalanced situation of DC voltage after improving, but does not have for the deviation for controlling DC voltage
There is effect.
Summary of the invention
The object of the present invention is to provide a kind of modulator approach suitable for single-phase cascade type photovoltaic DC-to-AC converter, the modulator approaches
Photovoltaic DC-to-AC converter output voltage waveforms quality can be improved in the unbalanced situation of each unit DC voltage, and is made each
Unit DC voltage automatically tracks the DC voltage instruction value that its MPPT module provides, so that controller no longer needs extra cell
DC voltage Balance route algorithm, reduces the complexity of control algolithm.
To achieve the above object, the technical solution adopted by the present invention is that：A kind of space of single-phase cascade type photovoltaic DC-to-AC converter
Vector modulation method, on the basis of Traditional Space vector modulation method, according to each unit DC voltage instantaneous value and its MPPT
The difference for the DC voltage instruction value that module provides determine the unit DC side should charge, discharge or DC voltage keep not
Become, in the one-dimensional space of single-phase inverter output vector, is exported according to the instantaneous direction of grid-connected inverters electric current from controller
The two side areas of voltage instruction value respectively select one it is all as next switch with the most consistent vector of each unit charge/discharge demand
The output vector of phase calculates duty further according to controller output voltage instruction value and level value corresponding to two output vectors
Than.
In the space vector modulating method of above-mentioned single-phase cascade type photovoltaic DC-to-AC converter, certain unit DC side should fill
Electricity, electric discharge or the judgment criteria that remains unchanged of DC voltage are：In the DC voltage instruction value that unit MPPT module provides
On the basis of a positive and negative error range is set, when then determine should lower than the lower limit of the error range for unit DC voltage instantaneous value
Charging, when the upper limit that unit DC voltage instantaneous value is more than the error range then determines discharge, when unit DC voltage wink
Duration, which is in error range, then determines that DC voltage remains unchanged.
In the space vector modulating method of above-mentioned single-phase cascade type photovoltaic DC-to-AC converter, single-phase inverter output vector
The one-dimensional space contains up to 3NA vector, N are concatenation unit number.
In the space vector modulating method of above-mentioned single-phase cascade type photovoltaic DC-to-AC converter, with each unit charge/discharge demand
The choosing method of most consistent vector is：It is each when judging using some vector according to the instantaneous direction of grid-connected inverters electric current
The variation tendency of unit DC voltage is denoted as 0 point if the charge/discharge demand with unit is consistent, if the charge/discharge with unit needs
It asks and disagrees, be denoted as 2 points, it is inconsistent if the charge/discharge demand with unit but 1 point is also denoted as if, by the vector to institute
There is the score of unit to sum, finally compare the total score of all vectors to be selected in same region, choosing the smallest vector of total score is
In the region with the most consistent vector of each unit charge/discharge demand.
In the space vector modulating method of above-mentioned single-phase cascade type photovoltaic DC-to-AC converter, the variation of each unit DC voltage
In trend, rises and be charged as unanimously, it is consistent for declining with electric discharge, and rising and discharging is to violate, decline and is charged as violating,
His situation be it is inconsistent but also without prejudice to.
Beneficial effects of the present invention are：Modified space vector modulation method is applied to photovoltaic generating system, instead of control
The part of unit DC voltage Balance route in device algorithm processed, simplified control device structure are conducive to improve stability of control system.
In photovoltaic generating system, modified space vector modulation expands the range of choice of optimal vectorial combination, makes light
Volt inverter output voltage approaches output voltage instruction value, output voltage waveforms quality is improved, to improve entire photovoltaic
The efficiency of electricity generation system.
Modulator approach of the invention considers dc-voltage balance problem, and output voltage waveforms quality can be improved.
Modulator approach proposed by the invention is not only suitable for monophase system and is also applied for three-phase system.
Detailed description of the invention
Fig. 1 (a) is the unit cascaded type photovoltaic power generation system structure schematic diagram of one embodiment of the invention single-phase three；Fig. 1 (b)
For H bridge structural schematic diagram in one embodiment of the invention Fig. 1 (a)；
Fig. 2 is the improved space vector modulation algorithm flow chart of one embodiment of the invention；
Fig. 3 is sequence of all possible output vector of one embodiment of the invention photovoltaic DC-to-AC converter in one-dimensional coordinate；
Vector and its affiliated set of vectors of the Fig. 4 for one embodiment of the invention photovoltaic DC-to-AC converter positive axis.
Specific embodiment
Embodiments of the present invention are described in detail with reference to the accompanying drawing.
The present embodiment proposes a kind of modulator approach that can be used for single-phase photovoltaic inverter, and this method is to Conventional spatial vector
Modulation improves, by preferably exporting switching vector selector, so that the direct current that the DC voltage of each unit follows its MPPT to provide
Instruction value is pressed, realizes each unit DC voltage fast convergence, and the item that inverter can be inconsistent in each unit DC voltage
It is accurately exported according to the output order value of control algolithm under part, improves output voltage waveforms quality.Use the light of the modulator approach
Lie prostrate inverter, it is no longer necessary to the DC voltage Balance route algorithm in its controller between extra cell, to reduce control
The complexity of device algorithm improves stability.
What the present embodiment was achieved through the following technical solutions, a kind of space vector tune of single-phase cascade type photovoltaic DC-to-AC converter
Method processed, the modulation algorithm is improved on the basis of traditional space vector modulating method, according to each unit direct current
The difference for the DC voltage instruction value that instantaneous voltage and its MPPT module provide determine the unit DC side should charge, discharge or
Be to maintain it is constant, in the one-dimensional space of single-phase inverter output vector, according to the instantaneous direction of grid-connected inverters electric current from control
The two side areas of device output voltage instruction value processed respectively select one with the most consistent vector of each unit charge/discharge demand as next
The output vector of a switch periods, further according to controller output voltage instruction value and level value meter corresponding to two output vectors
Calculate duty ratio.
Moreover, some unit DC side should charge, discharge or judgment criteria that DC voltage remains unchanged, it is at this
One positive and negative error range is set on the basis of the DC voltage instruction value that unit MPPT module provides, when unit DC voltage is instantaneous
Value then determines charge lower than the lower limit of the error range, when unit DC voltage instantaneous value is more than the upper limit of the error range
Then determine discharge, then determines that DC voltage remains unchanged when unit DC voltage instantaneous value is in error range.
Moreover, because there are three types of (+U for the output level of each unitdc、-UdcWith 0), and the direct current of all units is considered
All different situations is pressed, the one-dimensional space of the single-phase inverter output vector contains up to 3NA vector, N are concatenation unit
Number.
Moreover, being with the choosing method of the most consistent vector of each unit charge/discharge demand：According to grid-connected inverters electric current
Instantaneous direction judges the variation tendency using each unit DC voltage when some vector, if the charge/discharge demand one with unit
Cause is then denoted as 0 point, 2 points is denoted as if the charge/discharge demand with unit is disagreed, if the charge/discharge demand with unit is inconsistent
But also score of the vector to all units is summed, all vectors to be selected in same region are finally compared without prejudice to being then denoted as 1 point
Total score, the smallest vector of total score be in the region with the most consistent vector of each unit charge/discharge demand.Unit direct current
In the variation tendency of voltage, rising with charging unanimously, decline is consistent with electric discharge, rises and violates with electric discharge, and decline is violated with charging,
Other situations all can be regarded as it is inconsistent but also without prejudice to.
Implementation steps are as follows：
Step 1, single-phase N unit photovoltaic DC-to-AC converter all output vectors in the unequal situation of each unit DC voltage
Have 3NIt is a, by 3NA output vector gi(i=1,2 ...) presses its corresponding level value Pi(i=1,2 ...) size is divided.Each list
First DC voltage UdciThe sum of (i=1,2 ... N) are Udcsum, to the level values of all output vectors in-Udcsum、-Udcsum*(N-
1)/N、……-Udcsum/N、0、Udcsum/N……、Udcsum*(N-1)/N、UdcsumIt is most connect Deng finding in total 2N+1 numerical value with it
Close numerical value, and be divided into a set of vectors with the close vector of the same numerical value for all, then the output of single-phase N unit is sweared
Amount can be divided into 2N+1 set of vectors.
Step 2, each unit DC voltage instantaneous value U is measureddci, and define the DC voltage instruction that its MPPT module provides
The U of valuedcrefiError range be ± Δ d.If Udci>Udcrefi+ Δ d, then the unit needs to discharge；If Udci<UdcrefiΔ d,
Then the unit needs to charge；If Udcrefi-Δd<Udci<Udcrefi+ Δ d, then the unit DC voltage remains unchanged；
Step 3, in the one-dimensional space of all output vectors, in the left and right side of the output order value k of control algolithm
It finds out respectively and the immediate vector g of its numerical value1And g2。
Step 4, in step 3 gained g1、g2Affiliated set of vectors Gj、Gj+1Interior, find needs with each unit charge/discharge respectively
Ask most consistent vector as optimal output vector gopt1、gopt2.If more than 1 of the optimal vector in a set of vectors, is selected
Take its level numerical value near the vector of k.It finds as follows with the method for the most consistent vector of each unit charge/discharge demand：
According to inverter output current isInstantaneous direction, to each output vector in a set of vectors, to its with
The matching degree of the charge/discharge demand of all units scores.It is based on circuit theory analysis as a result, if i-th (i=1,
2 ...) discharge/charge of the trend that a vector can make the DC voltage of xth (i=1,2 ... N) a unit rise or fall and x unit
Electricity demanding is consistent, then remembers Six=0 point, S is remembered if the charge/discharge demand with x unit is disagreedix=2 points, if with the unit
Charge/discharge demand is inconsistent but also without prejudice to then remembering Six=1 point.Wherein in the variation tendency of unit DC voltage, direct current
Pressure rising is consistent with charge requirement, and DC voltage decline is consistent with electric discharge demand, and DC voltage rising is violated with electric discharge demand, directly
Galvanic electricity drops are violated with charge requirement, other situations all can be regarded as it is inconsistent but also without prejudice to.
Then, summation S is carried out to score of each output vector to all unitsi=∑ Six(x=1 ... N).One arrow
The least vector of total score is the optimal vector in the set of vectors in duration set.
Step 5, optimal output vector g is determinedopt1And gopt2Duty ratio in one cycle is Dopt1And Dopt2：Vector
gopt1And gopt2Corresponding level numerical value is respectively Popt1And Popt2, then output vector gopt1And gopt2The time acted on respectively is
Dopt1=(Popt2-k)/(Popt2-Popt1), Dopt2=1-Dopt1；
Step 6, pass through the optimal output vector g in step 5opt1、gopt2With duty ratio Dopt1、Dopt2Control next switch
The switch motion of period each photovoltaic cells H bridge.
In step 1, since photovoltaic cell is influenced by extraneous various factors, the photovoltaic cell output voltage of each unit can
It can be different from, then the numerical values recited relationship of N number of unit photovoltaic cell output voltage has a variety of different situations, and the present embodiment is set
Fixed is N number of all unequal situation of unit photovoltaic output voltage.Certainly, the identical situation of the DC voltage of unit is also wrapped
With which, the principle and application of the present embodiment modulator approach are not influenced.
In step 4, if Gj=Gj+1, i.e. the immediate vector in the left and right sides k belongs to the same set of vectors, then by this
Set of vectors is divided into two region of left and right of k, finds optimal vector in the two regions respectively.
It is further illustrated below by way of example, as shown in Fig. 1 (a), Fig. 1 (b), single-phase three unit cascaded type photovoltaic topology knot
Structure, since photovoltaic cell is influenced by extraneous factors such as temperature, intensity of illumination and photovoltaic cell shades, each unit DC voltage
Difference, three unit DC voltage size relations have a variety of different situations.Three units of this example are identical in temperature, illumination
Under different conditions, wherein first unit intensity of illumination is 1000W/m2；Second unit intensity of illumination is 1100W/m2, the
Three unit intensities of illumination are 1400W/m2.In modulator approach, by selecting suitable vectorial combination to accelerate each unit DC side
Voltage convergence, improves the efficiency of photovoltaic DC-to-AC converter output voltage quality and entire photovoltaic generating system.
The space vector modulating method of this example single-phase cascade type photovoltaic DC-to-AC converter is uneven in each unit DC voltage
When weighing apparatus, the range of choice for expanding output vector combination makes photovoltaic DC-to-AC converter actual output voltage approach output voltage instruction value, mentions
High photovoltaic inverter output voltage waveform quality.
As shown in Fig. 2, the realization of this example includes the following steps：
1) since the intensity of illumination of three unit photovoltaic cells is different, then the DC voltage of each unit is different, three units
DC side output voltage be respectively Udc1, Udc2, Udc3, then all output vectors of single-phase Unit three share 3N=33=27.
Output vector includes ± giAnd zero vector (i=1,2,3 ... 13), the corresponding level numerical value P of positive axis output vectori(i=1,2 ...
It 13) is Udc1、Udc2、Udc3、Udc2-Udc1、Udc3-Udc2、Udc3-Udc1、Udc1+Udc2-Udc3、Udc1+Udc3-Udc2、Udc2+Udc3-Udc1、
Udc1+Udc2、Udc1+Udc3、Udc2+Udc3) and Udc1+Udc2+Udc3.The corresponding level value of all output vectors of photovoltaic DC-to-AC converter is such as
Shown in Fig. 3.
By the corresponding level value of 27 output vectors of the single-phase photovoltaic DC-to-AC converter of Unit three in-Udcsum、
0、UdcsumIn totally 2 × 3+1=7 numerical value find with its immediate numerical value, by it is all with it is same
The close vector of numerical value is divided into a set of vectors, wherein Udcsum=Udc1+Udc2+Udc3.The 0, (U in positive axisdc2-Udc1)、
(Udc3-Udc2)、(Udc3-Udc1) numerical value closest to 0, i.e. its set of vectors G0；Udc1、Udc2、Udc3、(Udc1+Udc2-Udc3)、
(Udc1+Udc3-Udc2)、(Udc2+Udc3-Udc1) numerical value it is closeI.e. its set of vectors is G1；(Udc1+Udc2)、(Udc1+
Udc3)、(Udc2+Udc3) numerical value it is closeI.e. its set of vectors is G2；(Udc1+Udc2+Udc3) numerical value close to Udcsum,
I.e. its set of vectors is G3.Due to all output vectors of photovoltaic DC-to-AC converter in the one-dimensional space about origin symmetry, thus one
The negative semiaxis of dimension space also has 3 set of vectors, then 27 output vectors can be divided into (2 × 3)+1=7 set of vectors.
2) each unit DC voltage instantaneous value U is measureddci, DC voltage instruction value U that MPPT is provideddcrefiError model
It encloses for ± Δ d.According to UdciWith UdcrefiRelationship between Δ d determines the charge/discharge demand of each unit, and wherein Δ d can be with
Value is 0.01V or other suitable numerical value.
3) in the one-dimensional space of all output vectors, from the left and right side difference of the output order value k of control algolithm
It finds out and the immediate vector g of its numerical value1And g2。
4) g obtained by step 3)1、g2Affiliated set of vectors Gj、Gj+1It is interior, it finds and each unit charge/discharge demand respectively
Most consistent vector is as optimal output vector gopt1、gopt2.Find the side with the most consistent vector of each unit charge/discharge demand
Method is as follows：
The direction that photovoltaic inverter grid-connected sense of current takes Fig. 1 to be indicated is positive, to each of in a set of vectors
Output vector scores the matching degree of itself and the charge/discharge demand of all units.Knot based on circuit theory analysis
Fruit, if trend and x that i-th (i=1,2 ...) a vector rises or falls the DC voltage of xth (i=1,2 ... N) a unit
The charge/discharge demand of unit is consistent, then remembers Six=0 point, S is remembered if the charge/discharge demand with x unit is disagreedix=2 points, if
It is inconsistent with the charge/discharge demand of the unit but also without prejudice to then remembering Six=1 point.
Such as.If photovoltaic inverter grid-connected electric current is>0, in vector combination GjIt is interior, it is assumed that vector g1It is m-th of output arrow
Amount, level numerical value P1=Udc1+Udc2-Udc3, then according to circuit theory, Unit first and second exports electric energy, and third unit is defeated
Electric energy out, i.e. vector g1It will be so that Udc1And Udc2Decline, and Udc3Rise.Charge/discharge in conjunction with step 2 gained each unit needs
It asks, if needing to charge for first unit the case where three units, second unit needs to discharge, and third unit needs are put
Electricity, then according to above-mentioned method of scoring, vector g1To the respectively S that scores of three unitsm1=0, Sm2=2, Sm3=0, then swear
Measure g1Must be divided into 2.
Then, set of vectors G is calculatedjIn each output vector score Si=∑ Six(x=1 ... N) calculates total score
The smallest vector is the optimal vector g in the set of vectorsopt1.Similarly, set of vectors G can be calculatedj+1Interior optimal vector
gopt2。
As shown in figure 4, if the hithermost output vector of the left and right side of output order value belongs to identical set of vectors
Gj=Gj+1, and alternative output vector is less than two, then it is contemplated that selection time is close to set of vectors Gj-1Interior is defeated
Vector out, the optimal vector selected in this way can accelerate DC voltage to restrain, and improve output voltage output waveform quality.
5) by solution following equations group, g is acquiredopt1And gopt2Duty ratio D in a switch periodsopt1And Dopt2
Wherein Popt1For vector gopt1Corresponding level value, Popt2For vector gopt2Corresponding level value.
6) photovoltaic DC-to-AC converter is according to gopt1And gopt2Level value and duty ratio Dopt1、Dopt2, control next switch periods
The switch motion of each unit H bridge.
Through the above steps, different moments find optimal output vector, two optimal outputs in the left and right sides of k respectively
Vector modulation photovoltaic DC-to-AC converter output voltage instruction value, makes photovoltaic DC-to-AC converter output voltage accurately approach output voltage instruction value,
Restrain each unit DC voltage.
Space vector modulating method is applied to photovoltaic generating system by this example, and according to the spy of cascade connection type photovoltaic DC-to-AC converter
Point improves space vector modulation algorithm.The modulation algorithm can be accurately according to command voltage output voltage waveforms, together
When by the two sides of output order value find two optimal output vectors, meet the convergent requirement of unit DC side.This example
The level value that vector is accurately calculated according to unit real voltage makes a fiduciary level nearby have multiple similar level and vector
Available, selected optimal output vector combination greatly speeds up DC voltage convergence rate.
It should be understood that the part that this specification does not elaborate belongs to the prior art.
Although being described in conjunction with the accompanying a specific embodiment of the invention above, those of ordinary skill in the art should
Understand, these are merely examples, various deformation or modification can be made to these embodiments, without departing from original of the invention
Reason and essence.The scope of the present invention is only limited by the claims that follow.
Claims (5)
1. a kind of space vector modulating method of single-phase cascade type photovoltaic DC-to-AC converter, characterized in that in Traditional Space Vector Modulation
On the basis of method, the difference of the DC voltage instruction value provided according to each unit DC voltage instantaneous value and its MPPT module is determined
The unit DC side should charge, discharge or DC voltage remains unchanged, in the one-dimensional space of single-phase inverter output vector
In, according to the instantaneous direction of grid-connected inverters electric current from the two side areas of controller output voltage instruction value respectively select one with it is each
Output vector of the most consistent vector of unit charge/discharge demand as next switch periods, further according to controller output voltage
Instruction value calculates duty ratio with level value corresponding to two output vectors.
2. the space vector modulating method of single-phase cascade type photovoltaic DC-to-AC converter as described in claim 1, characterized in that certain unit
DC side should charge, discharge or judgment criteria that DC voltage remains unchanged is：It is provided in unit MPPT module straight
A positive and negative error range is set on the basis of stream voltage instruction value, when unit DC voltage instantaneous value is lower than under the error range
Limit then determine charge, when unit DC voltage instantaneous value be more than the error range the upper limit then determine discharge, work as list
First DC voltage instantaneous value, which is in error range, then determines that DC voltage remains unchanged.
3. the space vector modulating method of single-phase cascade type photovoltaic DC-to-AC converter as described in claim 1, characterized in that single-phase inverse
The one-dimensional space for becoming device output vector contains up to 3NA vector, N are concatenation unit number.
4. the space vector modulating method of single-phase cascade type photovoltaic DC-to-AC converter as described in claim 1, characterized in that with each list
The choosing method of first most consistent vector of charge/discharge demand is：According to the instantaneous direction of grid-connected inverters electric current, judge using certain
The variation tendency of each unit DC voltage when one vector is denoted as 0 point if the charge/discharge demand with unit is consistent, if with list
The charge/discharge demand of member is disagreed, and is denoted as 2 points, inconsistent if the charge/discharge demand with unit but 1 is also denoted as if
Point, score of the vector to all units is summed, finally compares the total score of all vectors to be selected in same region, selection must
Point the smallest vector is in the region and the most consistent vector of each unit charge/discharge demand.
5. the space vector modulating method of single-phase cascade type photovoltaic DC-to-AC converter as claimed in claim 4, characterized in that each unit
In the variation tendency of DC voltage, rises and be charged as unanimously, it is consistent for declining with electric discharge, and rising and discharging is to violate, and is declined
Be charged as violating, other situations be it is inconsistent but also without prejudice to.
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