CN106953525B - Impedance type multimode tandem photovoltaic DC booster converter - Google Patents
Impedance type multimode tandem photovoltaic DC booster converter Download PDFInfo
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- CN106953525B CN106953525B CN201710035966.2A CN201710035966A CN106953525B CN 106953525 B CN106953525 B CN 106953525B CN 201710035966 A CN201710035966 A CN 201710035966A CN 106953525 B CN106953525 B CN 106953525B
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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
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
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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
- H02M1/0003—Details of control, feedback or regulation circuits
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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 present invention provides a kind of impedance type multimode tandem photovoltaic DC booster converters, including quasi- Z source impedance network and full-bridge DC-DC converter；Wherein, the quasi- Z source impedance network and the cascade of full-bridge DC-DC converter constitute impedance type power conversion unit；For the input terminal of the impedance type power conversion unit for connecting photovoltaic array, output end is serially connected acquisition high direct voltage；The quantity of the impedance type power conversion unit is multiple.It further include single bipolarity conversion DC converter；The output end of multiple impedance type DC-DC converters accesses the input circuit of single bipolarity conversion DC converter after being connected in series.The present invention has good expansibility, has potential engineering application value for the development & construction of China's future large-sized DC photovoltaic plant and power generation base.
Description
Technical field
The present invention relates to impedance type converter circuit topologys and operation to control, and in particular, to a kind of impedance type multimode
Tandem photovoltaic DC booster converter.
Background technique
Photovoltaic power generation is one of most important form of current generation of electricity by new energy, is to realize renewable energy substitution China's future
Main force.China's illumination resource distribution situation determines Large scale construction with electric system pattern, concentrates grid integration that will become
The important form of the following photovoltaic development and utilization.
The inherent feature that there are power densities is small for photovoltaic power generation, exit potential is low, random fluctuation is big, it is necessary to be by collecting
The boosting convergence of system can reach grid-connected conditions.Conventional photovoltaic power station takes AC boosting to collect technology, i.e. photovoltaic array exports
Obtain stabilizing low voltage three-phase alternating current after MPPT control is with photovoltaic DC-to-AC converter, then by after bus convergence by step-up transformer
Access power distribution network.The program is applied to large-sized photovoltaic power generation base and is primarily present two big disadvantages:
1, the weak lower multi-inverter parallel stability problem of synchronous support is prominent, and voltage out-of-limit takes place frequently with wide frequency domain oscillation；
2, it exchanges between standing and collects that line loss is big, and system whole efficiency is relatively low in standing.
To solve the above problems, photovoltaic DC boosting, which can be used, collects system building large-sized DC photovoltaic power generation base, i.e.,
Photovoltaic array output low-voltage DC directly by photovoltaic DC booster converter pump rises to direct current distribution voltage level, by into
After one step is collected, is accessed by the concentration inversion of VSC converter station and exchange bulk power grid or by large size boosting rotary substation that voltage is further
It is raised to HVDC level, realizes that direct current photovoltaic power generation base is sent out at a distance.The program is developed suitable for large-scale photovoltaic power station
Construction, has obtained domestic and international academia, engineering circles extensive concern at present, has the bright outlook.National " 13 " emphasis is ground
This technology has been directed in hair special plan and has set up special project, carries out further investigation.Typical photovoltaic DC boosting collects system
As shown in Figure 1:
Developing photovoltaic DC booster converter is to realize that photovoltaic DC boosting collects the key point of access.The current transformer needs
Meet following technical requirements:
1, high step-up ratio is, it can be achieved that from photovoltaic array output end to the single-stage boosting inverter of direct current medium voltage distribution network；
2, good efficiency characteristic, it is ensured that photovoltaic DC boosting collects system whole efficiency and meets design requirement；
3, meet all kinds of operation demands for control of system, have high reliability and good operation adaptability.
High step-up ratio DC-DC converter currently used for photovoltaic generating system is broadly divided into monomer structure and multimode string
It is coupled structure two types.It is horizontal to be limited by circuit working mechanism, device technology, haplotype current transformer step-up ratio is limited, Wu Faman
Sufficient photovoltaic DC boosting collects system requirements.Block coupled in series type current transformer generally using isolated form DC-DC as sub- converter cell,
Using the pattern acquiring high step-up ratio of " independent/in parallel input-series connection output ".
In independent input mode (as shown in Figure 2), photovoltaic DC booster converter outlet side is cascaded structure.In ideal feelings
Under condition, current transformer exit potential Vout will be evenly distributed to each submodule, and it is equal everywhere to export electric current.When submodule each in system
When block input power unbalanced (that is: mismatch phenomenon), since Vout can be considered constant (being supported by external forceful electric power net), Vout will not
It evenly distributes again, part of module output voltage is reduced compared with rated value, remaining module output voltage will increase.To make photovoltaic array work
Make in MPPT point, each submodule input voltage is held essentially constant, it means that each submodule voltage gain will deviate from nominal number
Value.Full-bridge converter unit maximum boost capability is limited by the high frequency transformer turn ratio, after static system operating point determines, further
The space often very little for improving voltage gain, lacks flexible Secondary Control ability.Therefore, when power mismatch is more serious,
Part submodule voltage gain will be unable to meet system operation demand, and then lead to input side MPPT control failure, and outlet side goes out
Existing series current takes small effect, causes system generating capacity to decline, or even be unable to operate normally.In order to avoid the above problems,
Input power mismatch between submodule must be eliminated, it is ensured that power equalization.And condition is illuminated by the light between different photovoltaic array, physical parameter
The multiple factors such as difference influence, it is difficult to realize output power real time equaliser.
To solve aforementioned intrinsic contradictions, it is necessary to be improved to structure shown in Fig. 2, as shown in Figure 3, it may be assumed that in photovoltaic array
Low-voltage direct bus is set between photovoltaic DC booster converter, energy is tentatively collected.On this basis, by each submodule
Block input side parallel connection access low-voltage direct bus simultaneously introduces intermodule Balance route strategy.It is at this time guarantee photovoltaic array maximum work
Rate tracks precision, needs to configure dedicated distribution MPPT device between low-voltage direct bus and photovoltaic array.
Although scheme shown in Fig. 3 solves input power mismatch problems, but system complex, lead to reliability decrease.When low
When short trouble occurs in pressure any position of DC bus, will lead to whole photovoltaic arrays will move out operation.It is distributed simultaneously
The introducing of MPPT device brings difficulty to system operation and maintenance, is also unfavorable under external fault conditions executing station grade collaboration rapidly
Control guarantor's movement.
Photovoltaic DC module is directed in the document of the entitled high step-up ratio DC converter for photovoltaic DC module,
A kind of non-isolated high step-up ratio DC converter is had studied, which has the spies such as wide input voltage, high step-up ratio, high efficiency
Point.The detailed analysis topological structure and working principle of the converter, has carried out the correlation theory derivation of equation, it is straight to analyze photovoltaic
The external characteristics of flow module requires and describes corresponding control program.In conjunction with the electrical technology index of direct current photovoltaic generating module,
The 160W photovoltaic module experimental prototype based on the non-isolated high step-up ratio DC converter is devised, the experimental verification electricity is passed through
The correctness of the characteristics of road and theory analysis and Prototype Design.
But document research is the photovoltaic generating system based on DC bus, every piece of photovoltaic battery panel is coupled one
DC-DC converter, can independently realize MPPT, and multiple DC-DC converter parallel connections form DC bus, are incorporated to by public inverter
AC network.This system topology that collects based on DC bus may be implemented a certain range of boosting gain, but for
Boosting requires the grid-connected application scenarios of much higher direct current, and this topological structure is simultaneously not suitable for.
In entitled Multi-modular cascaded DC-DC converter for HVDC grid
It is disclosed in the document of connection of large-scale photovoltaic power systems: Large-
scale grid-connected photovoltaic(PV)energy conversion systems operate at low
voltage and are interfaced to medium-voltage and high-voltage ac utility
grids through one or two step-up voltage transformer stages.In addition,the
power conversion is performed with either a s ingle stage dc-ac converter
(central inverter)or a two stage dc-dc/dc-ac(string or multi-string
inverter).However,prime solar irradiation regions in the world are not always
located close to available utility lines,and in some cases are far away from
main consumption areas.Furthermore,long overhead transmissions lines(>400km)
and underwater transmission lines above 70kM,HVDC has become the most cost-
effective solution.Among HVDC technologies,voltage source converter based
HVDC system,mainly based on the modular multilevel converter(MMC),have become
popular due to smaller filters,multi-network connection and decoupling of
active and reactive power.This paper explores a new large-scale PV plant
configuration based on a dc-dc stage interfaced directly to an MMC based HVDC
system.Since PV systems are dc by nature,the proposed solution has several
advantages,particularly if combined directly with the HVDC power station.Some
power circuit topologies are presented,including their corresponding control
schemes.Simulation results are presented to provide a preliminary evaluation
on the operation and performance of the proposed system.
But the application background of document research is similar with the application, contributes to the photovoltaic hair for being incorporated to high-voltage direct current power grid
Electric direct current collects system, and the topological structure of use is also modularization cascade structure.But the modules of the document include two-stage
DC-DC converter: prime is isolation type DC-DC converter, and rear class is the export structure of full-bridge or half-bridge.This topological structure
While by way of module-cascade to improve step-up ratio, photovoltaic MPPT is also realized by preceding stage DC-DC converter.Two
The structure of grade DC-DC converter causes in circuit comprising more switching device, and the switching loss that when operation generates is larger, circuit
Structure and control strategy are also more complicated.
In entitled Power optimization strategy for cascaded dc-dc converter
It is disclosed in the document of architectures of photovoltaic modules: This paper proposes a
control strategy aiming at operating cascaded DC-DC converter architectures
of photovoltaic(PV)modules at maximum power irrespective of the irradiance
conditions,meanwhile meeting constraints of voltage-limitation type.The
global optimum of cascaded connections of PV modules is generally equivalent
with operating all the modules at maximum power point tracking(MPPT).The most
important disturbance occurs when the irradiance levels of modules are
sensibly different because of various reasons-in this case,voltage-limitation
requirements may be broken.The proposed supervising strategy then attempts to
establish the best suboptimal power regime.MATLABreg/Simulinkreg numerical
simulation results are presented in the case of a monophased grid-connected
PV system,where individual MPPTs have been implemented by extremum seeking
control(ESC).
But to collect system topology similar with the application for the photovoltaic DC of the use of the document, is all using multiple-variable flow
Device cascaded structure, the direct current of multiple photovoltaic array outputs are mutually gone here and there after DC-DC converter independent boosting
Connection, to obtain higher DC voltage, then realizes inversion grid connection.The DC-DC device that the document is selected is non-isolation type DC-DC
Converter, this accessible voltage gain range of converter is smaller, when external conditions such as intensities of illumination between each photovoltaic module
When there is larger difference, the module that will lead to cannot achieve the MPPT maximum power point tracking of photovoltaic.
Summary of the invention
For the defects in the prior art, the object of the present invention is to provide a kind of impedance type multimode tandem photovoltaic direct currents
Booster converter using novel sub- converter module unit of the quasi- Z source impedance network in conjunction with full-bridge converter and introduces double become
Cooperative control method is measured, impedance type multimode tandem direct current is constructed using independent input-series connection output mode on this basis
Booster converter.
Impedance type multimode tandem photovoltaic DC booster converter provided by the invention, including quasi- Z source impedance network and
Full-bridge DC-DC converter；
Wherein, the quasi- Z source impedance network and the cascade of full-bridge DC-DC converter constitute impedance type power conversion unit；
For the input terminal of the impedance type power conversion unit for connecting photovoltaic array, output end is serially connected acquisition direct current
High pressure；The quantity of the impedance type power conversion unit is multiple.
It preferably, further include single bipolarity conversion DC converter；
The output end of multiple impedance type DC-DC converters accesses single bipolarity conversion DC converter after being connected in series
Input circuit.
Preferably, the impedance type power conversion unit includes inductance L1, inductance L2, diode D1, diode D2, two poles
Pipe D3, diode D4, diode D5, transformer, capacitor C1, capacitor C2, capacitor C3, the S1 of switching tube, the S2 of switching tube, switch
The S3 of the pipe and S4 of switching tube；
One end of inductance L1 connects one end of the anode of diode D5, capacitor C2；The cathode of diode D5 connects inductance L2
One end, capacitor C1 one end；The other end connection other end of inductance L2 of capacitor C2, the C-terminal of the S1 of switching tube, switching tube
The C-terminal of S3；
One end of primary coil in the C-terminal of the S2 of the end the E connection switch pipe of the S1 of switching tube, transformer；The S3 of switching tube
The C-terminal of S4 of the end E connection switch pipe, in transformer primary coil the other end；
The other end of inductance L1 be electrode input end, the end E of the S2 of switching tube, the end E of the S4 of switching tube, capacitor C1 it is another
One end is negative input；
The cathode of the anode of one end diode D1 of secondary coil, diode D2 in transformer, the other end connect diode
The cathode of the anode of D3, diode D4；The cathode of diode D1, the cathode of diode D3, one end connection anode of capacitor C3 are defeated
Outlet, the anode of diode D2, the anode of diode D4, capacitor C2 the other end connect cathode output end.
Preferably, the MPPT control method of the impedance type power conversion unit uses climbing method.
It preferably, further include control system, the control system includes sampling module, state of a control identification module, control
Measure computing module and pulse modulation module；
Wherein, sampling module, for measuring the output information of photovoltaic array and the output information being passed to control shape
α and β information is passed to state of a control identification module simultaneously by state identification module；
The state of a control identification module, for generating state of a control variable SF according to α and β information, the output information；
The control amount computing module, for calculating α and β in real time according to state of a control variable SF；
The pulse modulation module, for generating corresponding switching device trigger signal and passing to full-bridge according to α and β
DC-DC converter；
Wherein, α is straight-through duty ratio；β is phase shifting angle.
Preferably, the control system includes mode control as follows:
Mode 1: when Δ P >=0, Δ UPV>=0, α > 0；Or Δ P < 0, Δ UPVWhen<0, α>0,
Δ P >=0, Δ UPV>=0 or Δ P<0, Δ UPVWhen < 0, it is left that the operating point of photovoltaic array is located at its P-V peak of curve
Side；To be close to maximum power point, U need to be madepvIncrease, U to be increasedpv, α need to be reduced or increase β；Due to α > 0, controller is preferential
α is to reduce circuit loss and stress for reduction, this season SF=1；
Wherein, Δ P is photovoltaic array output power incrementss between this sampling and last time sampling；ΔUPVFor this sampling with
Photovoltaic array output voltage incrementss between last time sampling；UpvFor photovoltaic array current output voltage；
Mode 2: when Δ P >=0, Δ UPV>=0, α≤0；Or Δ P < 0, Δ UPVWhen < 0, α≤0,
Δ P >=0, Δ UPV>=0 or Δ P<0, Δ UPVWhen < 0, photovoltaic array operating point is located on the left of its P-V peak of curve；
To be close to maximum power point, U need to be madepvIncrease, U to be increasedpv, α need to be reduced or increase β；Due to α=0, controller can only
Increase β, this season SF=2；
Mode 3: when Δ P >=0, Δ UPV<0, β>α；Or Δ P < 0, Δ UPVWhen >=0, β > α,
Δ P >=0, Δ UPV< 0 or Δ P < 0, Δ UPVWhen >=0, photovoltaic array operating point is located on the right side of its P-V peak of curve；
To be close to maximum power point, U need to be madepvReduce, U to be reducedpv, α need to be increased or reduce β；Due to β > α, controller preferentially reduces
β is to keep α as small as possible, this season SF=3；
Mode 4: when Δ P >=0, Δ UPV< 0, β≤α；Or Δ P < 0, Δ UPVWhen >=0, β≤α,
Δ P >=0, Δ UPV< 0 or Δ P < 0, Δ UPVWhen >=0, photovoltaic array operating point is located on the right side of its P-V peak of curve；
To be close to maximum power point, U need to be madepvReduce, U to be reducedpv, α need to be increased or reduce β；Due to β=α, controller will be synchronized
Increase β and α, this season SF=4.
Compared with prior art, the present invention have it is following the utility model has the advantages that
1, QZSDC submodular circuits have controllable boosting characteristic, can carry out on the basis of the high frequency transformer turn ratio flexibly
Secondary gain adjustment, increase each submodule working region, solve the problems, such as power mismatch between photovoltaic array, enhancing system operation is suitable
Ying Xing；
2, multiple photovoltaic arrays independently access submodule, no setting is required low-voltage direct bus, can simplify direct current and collect and are
Structure of uniting enhances system reliability convenient for the insulation blocking of internal fault；
3, contain quasi- Z source impedance network in submodular circuits, allow to introduce pass-through state, current transformer bridge can be resisted naturally
Arm shoot through failure enhances power electronic equipment operational reliability；
4, MPPT maximum power point tracking (MPPT) function and boosting inverter function are realized in same level-one converter, without adjoint
Header box (distributed MPPT device) is arranged in photovoltaic array, is convenient for system maintenance, and improving power station, integrally control is rung in special circumstances
Answer speed；
5, current transformer integrally uses the distributed control architecture based on each submodule, and each submodule closed loop control is
It, can lifting system reliability without communicating between system master control and submodule；
6, the present invention has good expansibility, and China future large-sized DC photovoltaic plant and power generation base are opened
Hair construction has potential engineering application value.
Detailed description of the invention
Upon reading the detailed description of non-limiting embodiments with reference to the following drawings, other feature of the invention,
Objects and advantages will become more apparent upon:
Fig. 1 is the schematic diagram that typical photovoltaic DC boosting collects system；
Fig. 2 is the schematic diagram that simple independent input formula collects system；
Fig. 3 is that the input type in parallel of the bus containing low-voltage direct collects system schematic；
Fig. 4 is that middle impedance type multimode tandem DC booster converter of the present invention and corresponding photovoltaic DC boosting collect and be
System structure chart
Fig. 5 is the topological structure schematic diagram of the impedance type power conversion unit based on quasi- Z source network in the present invention；
Fig. 6 is the non-pass-through state of the topological structure of the impedance type power conversion unit based on quasi- Z source network in the present invention
Equivalent circuit diagram；
Fig. 7 is the pass-through state of the topological structure of the impedance type power conversion unit based on quasi- Z source network in the present invention
Equivalent circuit diagram；
Fig. 8 is the flow chart of climbing method in the present invention；
Fig. 9 is QZSDC entirety control block diagram in the present invention；
Figure 10 is phase shifting angle of the present invention and straight-through duty ratio algorithm flow chart；
Figure 11 is the control pulse schematic diagram in the present invention in a switch periods on S1-S4；
Figure 12 is the solar irradiance schematic diagram in the present invention on photovoltaic array；
Figure 13 is QZSDC1-8 output voltage and series connection total voltage simulation result schematic diagram in the present invention；
Figure 14 is output voltage schematic diagram of the photovoltaic array 4 under MPPT control in the present invention；
Figure 15 is output current diagram of the photovoltaic array 4 under MPPT control in the present invention.
Specific embodiment
The present invention is described in detail combined with specific embodiments below.Following embodiment will be helpful to the technology of this field
Personnel further understand the present invention, but the invention is not limited in any way.It should be pointed out that the ordinary skill of this field
For personnel, without departing from the inventive concept of the premise, various modifications and improvements can be made.These belong to the present invention
Protection scope.
In the present embodiment, the present invention provides the impedance type multimode tandems for collecting system for photovoltaic DC boosting
DC booster converter.Collect system structure based on the code converter, as shown in figure 4, wherein dotted box portion is this patent
The impedance type multimode tandem DC booster converter of proposition.The quasi- source Z DC-DC converter as converter Neutron module
(QZSDC) physical circuit topology is as shown in Figure 5.Quasi- Z source impedance network and full-bridge DC-DC converter are cascaded, impedance type is constituted
Power conversion unit, the submodule unit as photovoltaic DC booster converter.Each photovoltaic array is connected respectively to boosting and becomes
The corresponding submodule input terminal of parallel operation, each submodule outlet side use cascaded structure.Each photovoltaic array direct current output is through each son
Module realizes MPPT and voltage lifting function simultaneously, and connects to form 30kV unipolarity DC voltage in outlet side.
In turn, it is bis- to be converted to ± 30kV via station level list bipolarity conversion DC converter for 30kV unipolarity direct current output
Polarity DC output, so that match with the method for operation of external dc power distribution network (note: can also be accessed by DC-AC converter station
Middle pressure AC distribution net).
Assuming that external dc power distribution network is the stochastic volatility of forceful electric power net, meter and photovoltaic output, then it is straight for what is proposed
Stream boosting collects system, and (note: being directed to every grade of circuit to forward constant voltage control model, defines its power injection side step by step for use
For front end, similarly hereinafter).In such a mode, front stage circuits are in current source characteristic to rear class, and the present invention is special in current source to external electrical network
Property.Specifically: collecting system output voltage is ± 30kV, is supported by external electrical network given；Single bipolarity converts DC converting
The exit potential that device controls impedance type multimode tandem DC booster converter is 30kV；Then independent control is corresponding for each submodule
Photovoltaic array exit potential, realize each array MPPT operation.
A. submodular circuits topology and principle
Collect system application environment for photovoltaic DC, proposes a kind of impedance type power conversion unit (i.e.: in this patent
Quasi-Z Source DC-DC Converter, QZSDC), as the submodule unit of direct current photovoltaic booster converter, such as scheme
Shown in 5.Its feature is summarized as follows:
1, continuous input current, the effect of inductance L1 guarantee its continuous input current, therefore this QZSDC submodule general
With photovoltaic module output characteristics；
2, due to the presence of impedance network, working condition is not only effectively improved reliable there are a special pass-through state
Property, and flexible boost capability is introduced, secondary booster control can be carried out on high frequency transformer turn ratio benchmark；
3, passive device voltage stress is lower.Traditional Z source network symmetrical configuration, capacitor are resistant to same voltage；But the submodule
Capacitor C2 voltage stress is smaller in block；
4 use the distributed control architecture based on each submodule, each submodule closed loop control；System master and submodule
It, can lifting system reliability without communication between block；
5, quasi- Z source network, input terminal and output end are total ground structure, are easily assembled, and EMI interference is reduced.
According to the turn-on and turn-off condition of two switching tubes above and below same bridge arm, the working condition of QZSDC can be divided into non-
Pass-through state and pass-through state, the equivalent circuit diagram difference of QZSDC is as shown in Figure 6 under both states.Wherein, when work is non-
When pass-through state, diode forward conducting；When work is in pass-through state, diode bears back-pressure cut-off.
When stable state, is balanced according to inductance voltage-second balance and capacitance charge, following result can be released:
Wherein, α=π T0/ T, T indicate the switch periods of QZSDC, T0Indicate the straight-through time in a switch periods, U1For
The output end voltage of QZSDC,
When converter is in non-pass-through state, impedance network outlet side voltage uiIt can be expressed as
It is hereby achieved that
By the working principle of above formula and full-bridge DC-DC converter, QZSDC output end voltage U is obtained2It can indicate are as follows:
Wherein,Indicate impedance network outlet side voltage value under pass-through state, β=π (T-Ton)/T is phase shifting angle, TonTable
Show S in one switch periods of converter1And S3The time opened simultaneously.
B. submodule MPPT control method
Realize that MPPT function there are several specific algorithms, herein using classical power observation method (climbing method).Its principle are as follows: week
Change to phase property photovoltaic array port voltage, output power finds maximum power with the output power before change after comparison changes
Point.Port voltage is incrementally increased with fixed step-length since a starting point, is then measured since port voltage variation is drawn
The size of the output power variation risen and direction further change photovoltaic array port after determining that output power is changed direction
Voltage, to search out maximum power point of photovoltaic array.Its flow chart, as shown in Figure 7.
C. submodule modulation/control strategy
In order to which the output voltage control of photovoltaic array in the maximum power point obtained by above-mentioned MPPT algorithm, need to be used shifting
Phase angle beta and straight-through duty cycle alpha carry out the voltage gain of each submodule of Collaborative Control.Here using bivariate Collaborative Control method into
The control of row submodule, basic thought are as follows: Collaborative Control is carried out to phase shifting angle and straight-through angle under certain constraints, is being met
It realizes that straight-through duty ratio minimizes under the premise of the given tracking of voltage, reduces stress impact brought by shoot through, optimization system
System performance.
Submodule control block diagram is illustrated in figure 8 (to contain: sampling module, state of a control identification module, control amount computing module
And pulse modulation module).Sampling module measures the output information (including this sampling and preceding sampled result) of photovoltaic array,
And pass it to state of a control identification module.α and β information passes to state of a control identification module simultaneously.Multi input amount is common
The state of a control variable SF for determining submodule is used to calculate α and β in real time in this, as the input of control amount computing module.Most
Eventually, pulse modulation module generates corresponding switching device trigger signal according to α and β.
State of a control variable SF is the description to system current control state, and the direct decision systems of value are controlled currently
Specific movement in period (specifically, referring to: regulative mode and direction to controlled volume α and β).
To guarantee that SF value uniquely determines under any operating point, need to carry out classifying rationally to system control state.Herein,
Submodule state of a control is divided into 4 kinds of modes, corresponding SF value is respectively 1,2,3,4.
Controlled volume α and β can be uniquely determined according to bivariate Collaborative Control method basic principle for every kind of specific mode
Regulative mode and direction.On this basis, according to a upper control period alpha and β value and preset adjusting step-length
The numerical value of α and β calculates in the complete cost control period, and then issues reference instruction to pulse modulation module.System control state is known
The detailed process not calculated with α/β, (wherein: gray background frame portion is divided into system control state recognizer) as shown in Figure 9.
Specific system control state divides (mode 1-4) and corresponding control action selects, and is summarized as follows:
(1) mode 1: Δ P >=0, Δ UPV>=0, α > 0；Or Δ P < 0, Δ UPV<0, α>0
Δ P >=0, Δ UPV>=0 or Δ P<0, Δ UPVWhen < 0, it is left that the operating point of photovoltaic array is located at its P-V peak of curve
Side.To be close to maximum power point, U need to be madepvIncrease, U to be increasedpv, α need to be reduced or increase β.Due to α > 0, controller is preferential
Reduce α to reduce circuit loss and stress.This season SF=1.
Wherein, Δ P is photovoltaic array output power incrementss between this sampling and last time sampling；ΔUPVFor this sampling with
Photovoltaic array output voltage incrementss between last time sampling；UpvFor photovoltaic array current output voltage；
(2) mode 2: Δ P >=0, Δ UPV>=0, α≤0；Or Δ P < 0, Δ UPV< 0, α≤0
Δ P >=0, Δ UPV>=0 or Δ P<0, Δ UPVWhen < 0, photovoltaic array operating point is located on the left of its P-V peak of curve.
To be close to maximum power point, U need to be madepvIncrease, U to be increasedpv, α need to be reduced or increase β.Due to α=0, controller can only
Increase β.This season SF=2.
(3) mode 3: Δ P >=0, Δ UPV<0, β>α；Or Δ P < 0, Δ UPV>=0, β > α
Δ P >=0, Δ UPV< 0 or Δ P < 0, Δ UPVWhen >=0, photovoltaic array operating point is located on the right side of its P-V peak of curve.
To be close to maximum power point, U need to be madepvReduce, U to be reducedpv, α need to be increased or reduce β.Due to β > α, controller preferentially reduces
β is to keep α as small as possible.This season SF=3.
(4) mode 4: Δ P >=0, Δ UPV< 0, β≤α；Or Δ P < 0, Δ UPV>=0, β≤α
Δ P >=0, Δ UPV< 0 or Δ P < 0, Δ UPVWhen >=0, photovoltaic array operating point is located on the right side of its P-V peak of curve.
To be close to maximum power point, U need to be madepvReduce, U to be reducedpv, α need to be increased or reduce β.Due to β=α, controller will be synchronized
Increase β and α.This season SF=4.
Resulting α and β is calculated according to foregoing control algorithm, will be pocessed by pulse modulation module, and then generates submodule
Trigger signal needed for switching device in block.Modulator approach used herein is phase shift/straight-through modulation method[21], it is corresponding to it
A switch periods in gate pole trigger signal generting machanism it is as shown in Figure 10.
Multi-tool block cascaded structure as shown in Figure 4, using 8 photovoltaic arrays as input power, wherein each photovoltaic
Array includes 25 parallel branches, and every parallel branch includes 15 photovoltaic cell component series connection, each photovoltaic cell component
Temperature is 25 DEG C, and illumination condition is controlled according to test requirements document.Photovoltaic module model SunPower SPR-305-WHT,
Maximum power point voltage under simulated conditions is about 825V.
Impedance type multimode tandem DC booster converter contains 8 QZSDC submodule units, physical circuit parameter
Are as follows: L1=L2=100 μ H, C1=C2=220 μ F, C3=100 μ F, the former pair side turn ratio n=1:4 of submodule medium/high frequency transformer, are opened
Frequency f=5kHz is closed, bipolarity and voltage on line side are ± 30kV.
In simulation process, when t=0-0.16s, the illumination of each photovoltaic array is identical with temperature condition；T=0.16-
When 0.4s, change the output power of each photovoltaic array with significantly illumination variation, with simulation system run in be likely to occur
Power mismatch situation.The waveform diagram changed over time as shown in figure 11 for the solar irradiance on each photovoltaic array.
The output voltage U of submodule 1-82And the total voltage of impedance type multimode tandem DC booster converter output
UtotalAs shown in figure 12.In figure 12 it can be seen that before input power mismatch occurs for system (t=0-0.16s), 8 sons
The output voltage of module is identical, is about 3750V.As t=0.16s, change the illumination condition of each photovoltaic array, temperature strip
Part is constant, makes the output power of photovoltaic array 1-8 that variation, the output voltage of submodule 1-8 in various degree occur and also occurs accordingly
Variation.After power swing occurs for system (t=0.16-0.4s), the submodule 1-8 output voltage after stablizing is in 4300V-
Within the scope of 3200V, booster converter outlet side connect total voltage due to rear class list bipolarity switching DC-DC converter control,
When power swing occurs for system without significant change, all-the-time stable is in 30kV or so.
When t=0.16s, the solar irradiance of photovoltaic array 4 is by 1000W/m2It is reduced to 880W/m2, constant in temperature condition
In the case of, for the maximum power point voltage of photovoltaic cell component without significant change, maximum power point electric current becomes 5A；Theoretically at this time
Array output voltage should be the sum of the maximum power point voltage of photovoltaic cell component in same series arm without significant change, defeated
Electric current strain out is about 125A.Simulation result can be seen that 4 output voltage of photovoltaic array in t=0-0.4s as shown in Figure 13
It is stable in about 820V；It is stable stable in about 122A in about 136A, t=0.16s-0.4s in t < 0.16s to export electric current, rings
Should rapidly, MPPT works well.It can be seen that each submodule is correct effective to the independent MPPT control of corresponding photovoltaic array.
Specific embodiments of the present invention are described above.It is to be appreciated that the invention is not limited to above-mentioned
Particular implementation, those skilled in the art can make various deformations or amendments within the scope of the claims, this not shadow
Ring substantive content of the invention.
Claims (4)
1. a kind of impedance type multimode tandem photovoltaic DC booster converter, which is characterized in that including quasi- Z source impedance network,
Full-bridge DC-DC converter and control system；
Wherein, the quasi- Z source impedance network and the cascade of full-bridge DC-DC converter constitute impedance type power conversion unit；
For the input terminal of the impedance type power conversion unit for connecting photovoltaic array, output end, which is serially connected, obtains direct current height
Pressure；The quantity of the impedance type power conversion unit be it is multiple, the photovoltaic array quantity be it is multiple；
The quasi- Z source impedance network carries out secondary booster control on high frequency transformer turn ratio benchmark；
The control system includes sampling module, state of a control identification module, control amount computing module and pulse modulation module；
Wherein, sampling module is known for measuring the output information of photovoltaic array and the output information being passed to state of a control
α and β information is passed to state of a control identification module simultaneously by other module；
The state of a control identification module, for generating state of a control variable SF according to α and β information, the output information；
The control amount computing module, for calculating α and β in real time according to state of a control variable SF；
The pulse modulation module, for generating corresponding switching device trigger signal and passing to full-bridge DC-DC according to α and β
Converter；
Wherein, α is straight-through duty ratio, and β is phase shifting angle, is walked according to a upper control period alpha and β value and preset adjusting
Long, the numerical value that α and β in this control period can be completed calculates；
The control system includes mode control as follows:
Mode 1: when Δ P >=0, Δ UPV>=0, α > 0；Or Δ P < 0, Δ UPVWhen<0, α>0,
Δ P >=0, Δ UPV>=0 or Δ P<0, Δ UPVWhen < 0, the operating point of photovoltaic array is located on the left of its P-V peak of curve；For to
Maximum power point is close, need to make UpvIncrease, U to be increasedpv, α need to be reduced or increase β；Due to α > 0, controller preferentially reduce α with
Reduce circuit loss and stress, this season SF=1；
Wherein, Δ P is photovoltaic array output power incrementss between this sampling and last time sampling；ΔUPVFor this sampling and last time
Photovoltaic array output voltage incrementss between sampling；UpvFor photovoltaic array current output voltage；
Mode 2: when Δ P >=0, Δ UPV>=0, α≤0；Or Δ P < 0, Δ UPVWhen < 0, α≤0,
Δ P >=0, Δ UPV>=0 or Δ P<0, Δ UPVWhen < 0, photovoltaic array operating point is located on the left of its P-V peak of curve；For to most
High-power point is close, need to make UpvIncrease, U to be increasedpv, α need to be reduced or increase β；Due to α=0, controller can only increase β,
This season SF=2；
Mode 3: when Δ P >=0, Δ UPV<0, β>α；Or Δ P < 0, Δ UPVWhen >=0, β > α,
Δ P >=0, Δ UPV< 0 or Δ P < 0, Δ UPVWhen >=0, photovoltaic array operating point is located on the right side of its P-V peak of curve；For to most
High-power point is close, need to make UpvReduce, U to be reducedpv, α need to be increased or reduce β；Due to β > α, controller reduces β preferentially to protect
It is as small as possible to hold α, this season SF=3；
Mode 4: when Δ P >=0, Δ UPV< 0, β≤α；Or Δ P < 0, Δ UPVWhen >=0, β≤α,
Δ P >=0, Δ UPV< 0 or Δ P < 0, Δ UPVWhen >=0, photovoltaic array operating point is located on the right side of its P-V peak of curve；For to most
High-power point is close, need to make UpvReduce, U to be reducedpv, α need to be increased or reduce β；Due to β=α, controller synchronous will increase β with
α, this season SF=4.
2. impedance type multimode tandem photovoltaic DC booster converter according to claim 1, which is characterized in that also wrap
Include single bipolarity conversion DC converter；
The output end of multiple impedance type DC-DC converters accesses the input of single bipolarity conversion DC converter after being connected in series
Circuit.
3. impedance type multimode tandem photovoltaic DC booster converter according to claim 1, which is characterized in that described
Impedance type power conversion unit includes inductance L1, inductance L2, diode D1, diode D2, diode D3, diode D4, two poles
Pipe D5, transformer, capacitor C1, capacitor C2, capacitor C3, switching tube S1, switching tube S2, switching tube S3 and switching tube S4；
One end of inductance L1 connects one end of the anode of diode D5, capacitor C2；The one of the cathode connection inductance L2 of diode D5
It holds, one end of capacitor C1；The other end of capacitor C2 connects the other end of inductance L2, the C-terminal of switching tube S1, the C-terminal of switching tube S3；
One end of primary coil in the C-terminal of the end the E connection switch pipe S2 of switching tube S1, transformer；The end the E connection of switching tube S3 is opened
Close the C-terminal of pipe S4, in transformer primary coil the other end；
The other end of inductance L1 be electrode input end, the end E of switching tube S2, the end E of switching tube S4, capacitor C1 the other end be negative
Pole input terminal；
The cathode of the anode of one end connection diode D1 of secondary coil, diode D2, the other end connect diode in transformer
The cathode of the anode of D3, diode D4；The cathode of diode D1, the cathode of diode D3, one end connection anode of capacitor C3 are defeated
Outlet, the anode of diode D2, the anode of diode D4, capacitor C3 the other end connect cathode output end.
4. impedance type multimode tandem photovoltaic DC booster converter according to claim 1, which is characterized in that described
The MPPT control method of impedance type power conversion unit uses climbing method.
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