CN103869872B - The intelligent control method of cascade multilevel photovoltaic grid-connected system MPPT maximum power point tracking - Google Patents
The intelligent control method of cascade multilevel photovoltaic grid-connected system MPPT maximum power point tracking Download PDFInfo
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Abstract
The present invention relates to a kind of intelligent control method of cascade multilevel photovoltaic grid-connected system MPPT maximum power point tracking, the method is applicable to the cascade multilevel photovoltaic grid-connected system be made up of photovoltaic battery panel group, cascaded inverter, signal detection module, control module and electrical network, comprise the following steps: step one, according to the topological structure founding mathematical models of cascade multilevel photovoltaic grid-connected system; Step 2, according to the span of the voltage modulated ratio of each inversion unit in mathematical model determination cascaded inverter; Step 3, control module carries out PWM control to each inversion unit in cascaded inverter simultaneously; Step 4, according to the voltage balancing control of mathematical model to inversion unit DC bus capacitor, reaches the maximum power output of cascade multilevel photovoltaic grid-connected system.Compared with prior art, the present invention can make cascade multilevel photovoltaic grid-connected generating system significantly improve conversion efficiency, and reaches the intelligentized control method of maximum power output.
Description
Technical field
The present invention relates to a kind of new energy technology, especially relate to a kind of intelligent control method of cascade multilevel photovoltaic grid-connected system MPPT maximum power point tracking.
Background technology
The energy is the important substance basis that the mankind depend on for existence and development, and being the power of world economy, is also the key factor affecting national security.Cause these limited energy reserves to be petered out along with the continuous exploitation of the mankind to fossil fuels utilizes, force every country in the world all be devoted to the development and utilization of new forms of energy.Greatly develop regenerative resource, replace fossil energy by regenerative resource comprehensively, carry out a new industrial revolution, be not only the needs for human survival, the inexorable trend of world economy sustainable development especially.
Distribution of solar energy extensively, rich reserves, the plurality of advantages such as clean, the safety of photovoltaic generating system, life-span long and maintenance is little, photovoltaic generation is considered to 21 century most important, most active new forms of energy.Photovoltaic industry and the market demand obtain fast development in recent years, and sun power has started by " supplementing the energy " role transforming to " substitute energy ".It is estimated, the solar system can also exist 4,500,000,000 years, and the energy that the annual sun provides is 1.5 ten thousand times of world population commodity consumption amount.The exploitation of sun power will obtain significant progress, will take on heavy responsibilities, will certainly become the leading energy from now in the transfer of world's energy structure.
When photovoltaic power generation technology is subject to extensive concern, the technical research of the core component of parallel network power generation---combining inverter has seemed very outstanding.Wherein, cascaded multilevel inverter, as the one of multi-electrical level inverter, has the advantage that other versions are incomparable.Concrete manifestation is as follows:
(1) to bear voltage low for single power device, without the need to dynamic voltage-balancing;
(2) output level number is many, and waveform improves;
(3) switching frequency is low, and electronic switching device loss is little;
(4) without the need to output transformer, structural volume and the loss of itself of system is substantially reduced;
(5) based on full-bridge circuit structure, modular combination is easily adopted to carry out extension system structure.
But must be pointed out, in cascade connection multi-level input circuit, the mutual imbalance of spread voltage on each capacitor of its DC side is that this circuit structure form " congenital " is not enough, and the phenomenon namely certainly existed is called for short " DC capacitor voltage is uneven "." DC capacitor voltage is uneven " can cause device withstand voltage uneven, and MPPT maximum power point tracking also can be made to encounter difficulties.Therefore, cascade multilevel photovoltaic grid-connected system effective implemention MPPT maximum power point tracking being enable, with regard to needing a kind of method can guaranteeing that DC capacitor voltage balances to maximize to realize power stage, the power factor that system exports can also be improved simultaneously.
Described " MPPT maximum power point tracking ", be the simple saying that photovoltaic maximum power point is followed the tracks of, English abbreviation is MPPT.Its essential meaning is: when photovoltaic array output voltage is smaller, along with the change of voltage, and output current change is very little, and photovoltaic array is similar is a constant current source; When voltage exceedes certain critical value continuation rising, electric current sharply declines, and photovoltaic array is now similar is a constant pressure source.The output power of photovoltaic array is then along with the rising of output voltage has an output power maximum point.The effect of maximal power tracing device is in the environment that all changes in temperature and radiation intensity, by change photovoltaic array with equivalent load, regulate the working point of photovoltaic array, photovoltaic array be operated on output power maximum point.In other words, the output characteristics of photovoltaic array has nonlinear characteristic, and it exports the impact by intensity of illumination, environment temperature and loading condition.But under certain intensity of illumination and environment temperature, when photovoltaic array is only operated in a certain magnitude of voltage, the output power of photovoltaic array just can reach maximal value, therefore in photovoltaic generating system, improve the whole efficiency of system, an important approach is exactly the working point adjusting photovoltaic array in real time, makes it to always work near maximum power point.
The change major effect solar cell output current size of solar radiation intensity of illumination, temperature variation major effect output voltage size.When temperature is identical, along with the increase of intensity of illumination, the open-circuit voltage of solar-energy photo-voltaic cell is almost constant, and because short-circuit current increases to some extent, corresponding peak power output increases; When intensity of illumination is identical, along with the rising of temperature, the open-circuit voltage of solar-energy photo-voltaic cell declines, although short-circuit current also increases to some extent, system peak power output reduces.The output power of photovoltaic array has a process of falling after rising along with the rising of output voltage.At certain temperature and light according under intensity, solar cell has unique maximum power point, when photovoltaic cell is operated in this, can export the peak power under Current Temperatures and intensity of illumination condition.The intersection point of load curve and solar cell current-voltage characteristic curve is the working point of solar cell.In order to obtain maximum output power, be necessary solar cell and load are matched.The maximum power output of solar-energy photo-voltaic cell array is mainly realized by adjustment load curve under varying ambient conditions, and this is also the fundamental basis of current all maximum power point tracing methods.Along with temperature and light is according to the change of intensity, constantly must adjusts output load working point, photovoltaic array is on corresponding peak power output point always.Described " MPPT maximum power point tracking of cascade multilevel photovoltaic grid-connected system ", just refers to the technical matters how going to realize MPPT maximum power point tracking in cascade multilevel photovoltaic grid-connected system.
For cascaded multilevel inverter, owing to there being multiple full bridge inverter (being called for short " inverter bridge "), can consider to realize MPPT by two kinds of methods.Generally traditional method carries out MPPT control to the output current of whole inverter and voltage sample, and this method controls simple, realizes being easier to; But because cascaded inverter adopts the input of multipath independent direct current source, the working condition of each inverter bridge has difference, adopts the MPPT of this traditional approach to produce power loss, can not ensure that each inverter bridge can both export with maximal efficiency.Therefore, MPPT must be used respectively to control to each inverter bridge, regulate the output voltage of each inverter bridge, the maximum power output of each inverter bridge could be realized, thus the efficiency of whole inverter could be improved.
Two kinds of modes are had: a kind of is the PWM dutycycle regulating inverter, and another kind is the voltage swing regulating input end DC bus capacitor to the regulation technology of bridge-type inverter output voltage.The former regulative mode is more convenient, but dutycycle too high or too low time, wave level can reduce, and then can cause waveform distortion.The input side of cascade connection multi-level photovoltaic DC-to-AC converter is photovoltaic array, output due to photovoltaic array is subject to the impact of temperature, intensity of illumination, output voltage can be caused unstable, will inevitably difference be there is in the DC input voitage of each inverter bridge, thus make the voltage at DC bus capacitor device two ends occur imbalance problem, the voltage causing electronic switching device to bear is inconsistent, portions of electronics switching device also being made time serious to damage because bearing high voltage stress, further negative effect being caused to MPPT control stiffness simultaneously.Therefore, the maximum power output of cascade connection multi-level photovoltaic DC-to-AC converter be realized, first must solve the balance of voltage problem of DC side input capacitor.
Find by prior art documents, Zhou Jiaqi, week dimension come, " control method of generating electricity by way of merging two or more grid systems of photovoltaic generation current transformer " (Chinese Patent Application No.: the control method of generating electricity by way of merging two or more grid systems that 201110341180.6) a kind of photovoltaic generation current transformer is provided of Zhang Zhe etc.It comprises line voltage software phlase locking, outer voltage foundation, Current Control and grid voltage orientation vector controlled, line voltage software phlase locking adopts the method for software three-phase phase-locked loop, phaselocked loop is made up of phase detector, loop filter and oscillator, grid voltage orientation vector controlled adopts two close cycles tandem type control structure: outer voltage, current inner loop, and Voltage loop controls DC bus-bar voltage; Electric current loop controls AC input current.This invention can be accomplished accurately directed, controls DC bus-bar voltage and stablizes, and realizes MPPT maximum power point tracking and controls.But, because this invention only carries out track with zero error design for electric current loop, the current-order that electric current loop provides according to Voltage loop controls AC input current, does not regulate accordingly DC capacitor voltage, is therefore in fact difficult to realize unity power factor and runs.
Also find by prior art documents again, " energy-saving type cascade multilevel photovoltaic grid-connected generating control system " (Chinese Patent Application No.: 201010234866.0) disclose a kind of energy-saving type cascade multilevel photovoltaic grid-connected generating control system of Ge Baoming.Wherein, multi-electrical level inverter is made up of multiple accumulation energy type photovoltaic generating module, and multiple block coupled in series is the phase in three-phase inverter, and each module single-stage power conversion realizes buck, inversion and energy storage, adapts to the wide region change of photovoltaic cell voltage.Photovoltaic cell and energy-storage battery are distributed in respective modules, and each module generating is independent to be controlled, and realizes distributed maximal power tracing.Because " each module generating is independent to be controlled " increases the complicacy of circuit structure, Technological Economy cost certainly will be increased, and reduce the reliability of system cloud gray model.
Summary of the invention
Object of the present invention is exactly provide a kind of intelligent control method of cascade multilevel photovoltaic grid-connected system MPPT maximum power point tracking to overcome defect that above-mentioned prior art exists, the method can make cascade multilevel photovoltaic grid-connected generating system significantly improve conversion efficiency, and reaches the intelligentized control method of maximum power output.
Object of the present invention can be achieved through the following technical solutions:
A kind of intelligent control method of cascade multilevel photovoltaic grid-connected system MPPT maximum power point tracking, the method is applicable to the cascade multilevel photovoltaic grid-connected system be made up of photovoltaic battery panel group, cascaded inverter, signal detection module, control module and electrical network, comprises the following steps:
Step one, according to the topological structure founding mathematical models of cascade multilevel photovoltaic grid-connected system;
Step 2, according to the span of the voltage modulated ratio of each inversion unit in mathematical model determination cascaded inverter;
Step 3, control module carries out PWM control to each inversion unit in cascaded inverter simultaneously;
Step 4, according to the voltage balancing control of mathematical model to inversion unit DC bus capacitor, reaches the maximum power output of cascade multilevel photovoltaic grid-connected system.
Cascade multilevel photovoltaic grid-connected system comprises: photovoltaic battery panel group, cascaded inverter, signal detection module, control module, electrical network.Photovoltaic battery panel group output interface is connected with the power input interface of cascaded inverter, the signal output interface of signal detection module is connected with the feedback signal input interface of control module, the steering order output interface of control module is connected with the steering order input interface of cascaded inverter, and the power output interface of cascaded inverter is connected with electrical network input interface.Photovoltaic battery panel group is under the irradiation of sunshine, there is photoelectric effect and produce corresponding d. c. voltage signal and export and be delivered to the power input interface of cascaded inverter by its output interface, signal detection module detects the feedback signal obtained transports to control module feedback signal input interface by its signal output interface, steering order is transported to cascaded inverter steering order input interface through its steering order output interface according to feedback signal computing by control module, and the power output signal of cascaded inverter is delivered to the input interface of electrical network through its power output interface.
Described photovoltaic battery panel group, is made up of multiple photovoltaic battery panel.Each photovoltaic battery panel is combined by multiple photovoltaic cells, forms a kind of flat matrix structure.In each photovoltaic battery panel, first form photovoltaic cell group by multiple photovoltaic cells, then form a photovoltaic battery panel by multiple photovoltaic cell group.Each photovoltaic cells output voltage signal in each photovoltaic cell group is connected in series one by one successively mutually, namely the positive pole termination of first photovoltaic cells is connected with the negative pole termination of second photovoltaic cells, the like, the last positive and negative output termination being become each photovoltaic cell group by the positive pole termination of last photovoltaic cells of each photovoltaic cell group with the negative pole end capitiform of first photovoltaic cells, namely operationally can obtain the addition of each photovoltaic cells output voltage signal.Corresponding by the positive and negative output termination of multiple photovoltaic cell group again and positive and negative output termination fetched as each photovoltaic battery panel, namely the positive and negative output termination of each photovoltaic cell group is connected with each other, operationally can be formed to have enough electric power and export.Multiple photovoltaic battery panel is arranged together just forms photovoltaic battery panel group, separate between each photovoltaic battery panel, their not directly connections mutually on electrically i.e., but the positive and negative output termination of each photovoltaic battery panel is corresponding with the positive and negative input termination of inversion unit each in cascaded inverter respectively connects.The output interface of photovoltaic battery panel group is formed side by side by the positive and negative output termination of each photovoltaic battery panel.
Described cascaded inverter, is made up of multiple inversion unit.The positive and negative input termination of each inversion unit separately and connect a capacitor, correspondingly with the positive and negative output termination of photovoltaic battery panel again to connect, namely form the power input interface of cascaded inverter side by side independently of each other by the positive and negative input termination of each inversion unit.The positive and negative input termination of each inversion unit and the capacitor connect is referred to as cascaded inverter DC bus capacitor, the voltage that each capacitor of cascaded inverter DC side produces is referred to as cascaded inverter DC capacitor voltage, or is referred to as cascaded inverter input side capacitance voltage.Connect mutually in the output termination of each inversion unit, namely the left output termination of first inversion unit connects the right output termination of second inversion unit, the left output termination of second inversion unit connects the right output termination of the 3rd inversion unit, by that analogy, the left output termination of penultimate inversion unit connects the right output termination of last inversion unit, finally with the right output termination of the left output termination of last inversion unit and first inversion unit be cascaded inverter two export terminations.Because cascaded inverter is formed by multiple inversion unit cascade, so be referred to as cascaded multilevel inverter, be called for short cascaded inverter.Described inversion unit is a kind of bridge circuit be made up of 4 power electronic devices, also known as H bridge.
Described signal detection module, comprising: input interface, front end signal processor and output interface.The photovoltaic voltage signal input part head of input interface exports termination with each photovoltaic battery panel positive and negative electrode and is connected, inverter output voltage signal input part head and each inversion unit of input interface export termination and are connected, and the mains voltage signal input termination of input interface is connected with grid side voltage measuring point; The output termination of input interface is connected with the input termination of front end signal processor; The output termination of front end signal processor is connected with the input termination of output interface, and the output termination of output interface is connected with the feedback signal input interface of control module.That is, signal detection module detects the voltage signal of positive and negative output termination, the output voltage signal of each inversion unit of each photovoltaic battery panel simultaneously, and the voltage signal of grid side.
In the mathematical model of step one, set up cascade multilevel photovoltaic grid-connected system output current/voltage equation as follows:
Wherein, L is electrical network equivalent inductance value; R is electrical network equivalent resistance; V
gfor line voltage value; V
nbe the n-th inversion unit output voltage values, it and the n-th inversion unit input voltage value
namely the magnitude of voltage on corresponding DC bus capacitor device
have inversion unit input/output voltage equation as follows:
Wherein, d
nfor the voltage modulated ratio of inversion unit.
Magnitude of voltage on DC bus capacitor device, that is the n-th inversion unit input voltage value
with inversion unit input end electric current
constituent relation equation is again:
Wherein, C is the capacitance of inversion unit DC bus capacitor device;
for appearing at the magnitude of voltage on the n-th inversion unit DC bus capacitor device, c represents inversion unit DC bus capacitor device;
be the n-th inversion unit input end electric current and the n-th photovoltaic battery panel output current value, p represents photovoltaic battery panel; I
nit is the n-th inversion unit output current value.N=1,2 ..., N, the N photovoltaic battery panel quantity included by photovoltaic battery panel group.
N-th inversion unit output current value I
nthe series electrical flow valuve I exported time grid-connected with cascade connection multi-level photovoltaic system again forms inversion unit two ends power-balance relation equation and is:
As I=0,
and then following equation can be obtained from formula () and formula (two):
Because
can be expressed as:
(formula six)
Wherein,
it is the n-th inversion unit output voltage amplitude; ω is the n-th inversion unit output voltage signal angular frequency;
it is the n-th inversion unit output voltage signal initial phase.
(formula six) is substituted into (formula five) obtain:
(formula seven)
Can be found out by (formula seven),
limited size in photovoltaic effect, belong to uncontrollable parameter, therefore only have by d
nwith
adjustment just can reach cascade multilevel photovoltaic grid-connected system to grid side voltage V
gcritical balance, namely both errors are close to minimum.
Step 2 determination inversion unit voltage modulated compares d
nspan
Because V
gfor fixed value, when pursuing the critical balance of (formula seven), d
ncan not be excessive, otherwise the minimizing of level and the distortion of waveform can be caused, therefore need to determine d
nrange of adjustment, namely | d
n|≤D.The value of D is determined by experiment, as: D=1, now ,-1≤d
n≤ 1.
Adopt voltage type PWM or current type PWM in step 3, and control the output voltage signal of each inversion unit by same pwm control signal simultaneously.
Step 4 DC capacitor voltage balance controls, and comprises step by step following:
Step by step 1, regulate the size of inversion unit voltage modulated ratio;
Adopt voltage dicyclo to add the control method of electric current loop, by the superposition of multiple error signal, obtain inversion unit voltage modulated than signal d
n.
Step by step 2, regulate the magnitude of voltage of the DC bus capacitor of inversion unit: first adopt voltage close loop to control the average voltage of the magnitude of voltage of each inversion unit DC bus capacitor and all inversion unit DC bus capacitors to compare, the error signal of acquisition is used for the initial phase adjusting corresponding inversion unit, the magnitude of voltage of the DC bus capacitor of this inversion unit is changed, then according to the distribution of power proportions, inversion unit is redistributed, then regulate the output valve of each inversion unit; The current value producing needs and compensate is compared, for keeping magnitude of voltage and the compensation power loss of DC bus capacitor simultaneously by each inversion unit output current value and marker signal reference current value;
Step by step 3, compare the size of the magnitude of voltage of inversion unit DC bus capacitor and the average voltage of all inversion unit DC bus capacitors, when
time, return step by step 1; When
time, perform step by step 4; In formula,
the magnitude of voltage of each inversion unit DC bus capacitor,
for the mean value of all inversion unit DC capacitor voltages, ε is by testing the enough little parameter determined;
Step by step 4, process obtains critical equilibrium point, calculates
value, and with the actual measurement magnitude of voltage of voltage measuring point in electrical network
compare, when
time, return step by step 1; When
time, return step 4, continue to follow the tracks of the maximum power point of cascade multilevel photovoltaic grid-connected system; Wherein, σ is the enough little parameter determined by electric system standard.
The value of parameter ε can be taken as 0.01, and the value of parameter σ can be taken as 0.05.
Compared with prior art, the each inversion unit of the present invention to each cascaded inverter carries out MPPT maximum power point tracking control simultaneously, by on the basis that regulates at PWM, each inversion unit input/output voltage modulation ratio and DC capacitor voltage are regulated, each inversion unit output waveform degree of distortion is made to drop to minimum, the output power of photovoltaic battery panel group is made to reach maximal value, the final MPPT maximum power point tracking obtaining cascade multilevel photovoltaic grid-connected system.
Accompanying drawing explanation
Fig. 1 is the process flow diagram of each step of the present invention;
Fig. 2 is the structural drawing of cascade multilevel photovoltaic grid-connected system.
Embodiment
Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.
Embodiment
As shown in Figure 1, a kind of intelligent control method of cascade multilevel photovoltaic grid-connected system MPPT maximum power point tracking, the method is applicable to by photovoltaic battery panel group 1, cascaded inverter 2, signal detection module 3, the cascade multilevel photovoltaic grid-connected system that control module 4 and electrical network 5 form, the structure of this system as shown in Figure 2, photovoltaic battery panel group 1 output interface is connected with the power input interface of cascaded inverter 2, the signal output interface of signal detection module 3 is connected with the feedback signal input interface of control module 4, the steering order output interface of control module 4 is connected with the steering order input interface of cascaded inverter 2, the power output interface of cascaded inverter 2 is connected with electrical network 5 input interface.Photovoltaic battery panel group 1 is under the irradiation of sunshine, there is photoelectric effect and produce corresponding d. c. voltage signal and export and be delivered to the power input interface of cascaded inverter 2 by its output interface, signal detection module 3 detects the feedback signal obtained transports to control module 4 feedback signal input interface by its signal output interface, control module 4 is after to the computing of feedback signal, steering order is transported to cascaded inverter 2 steering order input interface through its steering order output interface, the power output signal of cascaded inverter 2 is delivered to the input interface of electrical network 5 through its power output interface.
Described " feedback signal ", comprising: each photovoltaic battery panel positive and negative electrode output voltage signal, each inversion unit output voltage signal and grid side voltage signal.
Wherein, photovoltaic battery panel group 1 is made up of multiple photovoltaic battery panel 11 ~ 1N, the photovoltaic battery panel number that N comprises for photovoltaic battery panel group 1.Each photovoltaic battery panel is combined by multiple photovoltaic cells, forms a kind of flat matrix structure.In each photovoltaic battery panel, first form photovoltaic cell group by multiple photovoltaic cells, then form a photovoltaic battery panel by multiple photovoltaic cell group.Each photovoltaic cells output voltage signal in each photovoltaic cell group is connected in series one by one successively mutually, namely the positive pole termination of first photovoltaic cells is connected with the negative pole termination of second photovoltaic cells, the like, finally become the positive and negative output termination of each photovoltaic cell group with the negative pole end capitiform of first photovoltaic cells by the positive pole termination of last photovoltaic cells of each photovoltaic cell group.Corresponding by the positive and negative output termination of multiple photovoltaic cell group again and connect using the positive and negative output termination as each photovoltaic battery panel.Multiple photovoltaic battery panel 11 ~ 1N is arranged together just forms photovoltaic battery panel group 1, separate between each photovoltaic battery panel 11 ~ 1N, their not directly connections mutually on electrically i.e., but the positive and negative output termination of each photovoltaic battery panel 11 ~ 1N is corresponding with the positive and negative input termination of inversion unit 21 ~ 2N each in cascaded inverter 2 respectively connects.The output interface of photovoltaic battery panel group 1 is formed side by side by the positive and negative output termination of each photovoltaic battery panel 11 ~ 1N.
Cascaded inverter 2 is made up of multiple inversion unit 21 ~ 2N, the inversion unit number that N comprises for cascaded inverter 2.The positive and negative input termination of each inversion unit 21 ~ 2N is separately corresponding with the positive and negative output termination of photovoltaic battery panel 11 ~ 1N to be connected, and is namely made up of the power input interface of cascaded inverter 2 side by side the positive and negative input termination of each inversion unit 21 ~ 2N.Connect mutually in the output termination of each inversion unit 21 ~ 2N, namely the left output termination of first inversion unit 21 connects the right output termination of second inversion unit 22, the left output termination of second inversion unit 22 connects the right output termination of the 3rd inversion unit 23, by that analogy, the left output termination of penultimate inversion unit 2 (N-1) connects the right output termination of last inversion unit 2N, finally with the right output termination of the left output termination of last inversion unit 2N and first inversion unit 21 be cascaded inverter 2 two export terminations.
Signal detection module 3 comprises: input interface, front end signal processor and output interface.The photovoltaic voltage signal input part head of input interface exports termination with each photovoltaic battery panel 11 ~ 1N positive and negative electrode and is connected, the inverter output voltage signal input part head of input interface exports termination with each inversion unit 21 ~ 2N and is connected, and the mains voltage signal input termination of input interface is connected with electrical network 5 side voltage measuring point; The output termination of input interface is connected with the input termination of front end signal processor, and the output termination of front end signal processor is connected with the input termination of output interface, and the output termination of output interface is connected with the feedback signal input interface of control module 4.By this connection signal detection module 3 except detecting the voltage signal of positive and negative output termination, the output voltage signal of each inversion unit of each photovoltaic battery panel, and the voltage signal of grid side.
The concrete steps of the intelligent control method of MPPT maximum power point tracking of the present invention as shown in Figure 1, comprise
Step one, according to the topological structure founding mathematical models of cascade multilevel photovoltaic grid-connected system.
Cascade connection multi-level photovoltaic system output end current/voltage equation is set up by inversion unit 21 ~ 2N input end current/voltage equation, input/output voltage equation, two ends power-balance relation:
Because cascade multilevel photovoltaic grid-connected system output current/voltage equation is as follows:
Wherein, L is electrical network equivalent inductance value; R is electrical network equivalent resistance; V
gfor line voltage value; V
nbe the n-th inversion unit output voltage values, it and the n-th inversion unit input voltage value
namely the magnitude of voltage on corresponding DC bus capacitor device
have inversion unit input/output voltage equation as follows:
Wherein, d
nfor the voltage modulated ratio of inversion unit.
Magnitude of voltage on DC bus capacitor device, that is the n-th inversion unit input voltage value
with inversion unit input end electric current
constituent relation equation is again:
Wherein, C is the capacitance of inversion unit DC bus capacitor device;
for appearing at the magnitude of voltage on the n-th inversion unit DC bus capacitor device, c represents inversion unit DC bus capacitor device;
be the n-th inversion unit input end electric current and the n-th photovoltaic battery panel output current value, p represents photovoltaic battery panel; I
nit is the n-th inversion unit output current value.N=1,2 ..., N, the N photovoltaic battery panel quantity included by photovoltaic battery panel group.
N-th inversion unit output current value I
nthe series electrical flow valuve I exported time grid-connected with cascade connection multi-level photovoltaic system again forms inversion unit two ends power-balance relation equation and is:
As I=0,
and then following equation can be obtained from (formula one) and (formula two):
Because
can be expressed as:
(formula six)
Wherein,
it is the n-th inversion unit output voltage amplitude; ω is the n-th inversion unit output voltage signal angular frequency;
it is the n-th inversion unit output voltage signal initial phase.
(formula six) is substituted into (formula five) obtain:
(formula seven)
Can be found out by (formula seven),
limited size in photovoltaic effect, belong to uncontrollable parameter, therefore only have by d
nwith
adjustment just can reach cascade multilevel photovoltaic grid-connected system to grid side voltage V
gcritical balance, namely both errors are close to minimum.
Step 2, according to the span of the voltage modulated ratio of each inversion unit in mathematical model determination cascaded inverter.Because V
gfor fixed value, (formula seven) be made to reach critical balance, d
njust can not can not be excessive, otherwise the minimizing of level and the distortion of waveform can be caused, therefore need to determine d
nrange of adjustment, namely | d
n|≤D.The value of D is determined by experiment, in the present embodiment, makes D=1, now, and-1≤d
n≤ 1.
Step 3, control module adopts dsPIC33FJ64MC506 chip, each inversion unit is carried out simultaneously to the duty cycle adjustment under same pwm signal.
DsPIC33FJ64MC506 chip is the Novel 16-bit high performance digital signal controller that Microchip company releases.It combines the control advantage of single-chip microcomputer and the high-speed computation characteristic of digital signal processor (DSP), for embedded system provides one chip solution.It inherits Harvard's bus structure and reduced instruction set computer (RISC) technology of PIC single chip microcomputer series, and addressing mode is simple, travelling speed is fast, low in energy consumption, kinetic force is strong, be integrated with the DSP function of mainboard level simultaneously, powerful digital signal processing capability can be provided.In addition, additionally provide peripheral interface as abundant in UART, CAN, SPI etc., can carry out with other equipment easily communicating interconnected.Meanwhile, dsPIC33F adopts the Harvard structure processor of 16 and strengthens instruction set, comprising the support to digital signal processing.Its CPU has 24 bit instruction words, the opcode field of a variable-length.Programmable counter PC is 24 bit wides, and least significant bit (LSB) is 0, except some special instructions, in program normally performs, always ignores its highest significant position.Therefore, programmable counter PC can the user memory space of addressing 4M, and the highest addressing can reach the user storage space of 4M × 24.But cycles per instruction prefetch mechanisms is with helping maintain handling capacity and provide predictable execution.Except the instruction of reprogramming stream, double word move and table meter reading write command, all instructions all complete execution within the single cycle.Use DO and REPEAT instruction support without the program loop structure of expense, at any time can interrupt the execution of these two instructions.
Step 4, DC capacitor voltage balance controls, and comprising: step by step 1, regulates inversion unit voltage modulated to compare d
nsize; Step by step 2, regulate inversion unit DC capacitor voltage
balance; Step by step 3, compare
with
size; Step by step 4, seek grid-connected critical balance.Wherein:
Step by step 1, equally by dsPIC33FJ64MC506 chip as software carrier, adopt voltage dicyclo to add the control method of electric current loop, by the superposition of multiple error signal, obtain inversion unit voltage modulated than signal d
n.
Step by step 2, first controlled each inversion unit input side capacitance voltage value by voltage inter-loop
with the mean value of all inversion unit input side capacitance voltages
compare, the error signal obtained for adjusting the initial phase of corresponding inversion unit
cause its DC capacitor voltage value generation respective change.Secondly, the distribution of output voltage values according to power proportions is redistributed inversion unit, then regulates the output of each inversion unit.Meanwhile, the current value producing needs and compensate is compared, for holding capacitor magnitude of voltage and compensation power loss by each inversion unit output current value and marker signal reference current value.
Step by step 3, when
time, return step by step 1, continue to perform corresponding computing; When
Time, perform following step by step 4.
Step by step 4, calculate
numerical value, and with the actual measurement magnitude of voltage of power network
compare.
When
time, return step by step 1, continue to perform corresponding computing; When
time, return step 4, continue to perform the whole-process control to cascade multilevel photovoltaic grid-connected system.
Result of implementation confirms:
(1) the present invention carries out MPPT control to each inversion unit simultaneously, can guarantee that the output voltage of each inversion unit has same dutycycle, therefore, it is possible to establish and further regulate basis for the DC capacitor voltage balance of each inversion unit.
(2) by the adjustment to each inversion unit input/output voltage modulation ratio and DC capacitor voltage, each inversion unit output waveform degree of distortion is made to drop to minimum.
(3) final obtain " MPPT maximum power point tracking of cascade multilevel photovoltaic grid-connected system " reaches splendid effect, and namely the output power of photovoltaic battery panel group reaches maximal value.
Claims (6)
1. the intelligent control method of a cascade multilevel photovoltaic grid-connected system MPPT maximum power point tracking, the method is applicable to the cascade multilevel photovoltaic grid-connected system be made up of photovoltaic battery panel group, cascaded inverter, signal detection module, control module and electrical network, it is characterized in that, comprise the following steps:
Step one, according to the topological structure founding mathematical models of cascade multilevel photovoltaic grid-connected system;
Step 2, according to the span of the voltage modulated ratio of each inversion unit in mathematical model determination cascaded inverter;
Step 3, control module carries out PWM control to each inversion unit in cascaded inverter simultaneously;
Step 4, according to the voltage balancing control of mathematical model to inversion unit DC bus capacitor, reaches the maximum power output of cascade multilevel photovoltaic grid-connected system;
Described photovoltaic battery panel group comprises multiple photovoltaic battery panel, and each photovoltaic battery panel is combined by multiple photovoltaic cells, described cascaded inverter comprises the inversion unit of multiple cascade, and the positive and negative input termination of each inversion unit separately and connect a capacitor, then connects with the positive and negative output termination of corresponding photovoltaic battery panel is corresponding, described signal detection module, comprise input interface, front end signal processor and output interface, the photovoltaic voltage signal input part head of input interface and each photovoltaic battery panel are just, negative electrode exports termination and connects, inverter output voltage signal input part head and each inversion unit of input interface export termination and are connected, the mains voltage signal input termination of input interface is connected with the voltage measuring point of electrical network, the output termination of input interface is connected with the input termination of front end signal processor, the output termination of front end signal processor is connected with the input termination of output interface, the output termination of output interface is connected with the feedback signal input interface of control module, signal detection module connects each photovoltaic battery panel and each inversion unit, detects the voltage signal of the positive and negative output termination of each photovoltaic battery panel, the output voltage signal of each inversion unit and the voltage signal of electrical network simultaneously.
2. the intelligent control method of a kind of cascade multilevel photovoltaic grid-connected system MPPT maximum power point tracking according to claim 1, is characterized in that, in the mathematical model described in step one, obtains following formula thus establish regulating d by theory deduction
nwith
cascade multilevel photovoltaic grid-connected system can be reached to grid side voltage V
gthe theoretical foundation of critical balance:
In formula, V
gfor the magnitude of voltage of electrical network, the photovoltaic battery panel quantity of N included by photovoltaic battery panel group, d
nfor the voltage modulated ratio of inversion unit,
be the n-th inversion unit output voltage amplitude, ω is the n-th inversion unit output voltage signal angular frequency,
it is the n-th inversion unit output voltage signal initial phase;
The voltage equation of DC bus capacitor:
In formula,
be the n-th inversion unit input end electric current or the n-th photovoltaic battery panel output current value, p represents photovoltaic battery panel, I
nbe the n-th inversion unit output current value, C is the capacitance of inversion unit DC bus capacitor device;
for appearing at the magnitude of voltage of magnitude of voltage on the n-th inversion unit DC bus capacitor device or the n-th inversion unit input end;
The power-balance relation equation of inversion unit input end and output terminal:
In formula, I be cascade connection multi-level photovoltaic system grid-connected time export series electrical flow valuve, V
nbe the output voltage values of the n-th inversion unit,
for appearing at the magnitude of voltage of magnitude of voltage on the n-th inversion unit DC bus capacitor device or the n-th inversion unit input end.
3. the intelligent control method of a kind of cascade multilevel photovoltaic grid-connected system MPPT maximum power point tracking according to claim 2, is characterized in that, the span of step 2 voltage modulated ratio is | d
n|≤D, and D=1.
4. the intelligent control method of a kind of cascade multilevel photovoltaic grid-connected system MPPT maximum power point tracking according to claim 1, it is characterized in that, adopt voltage type PWM or current type PWM in step 3, and control the output voltage signal of each inversion unit by same pwm control signal simultaneously.
5. the intelligent control method of a kind of cascade multilevel photovoltaic grid-connected system MPPT maximum power point tracking according to claim 2, it is characterized in that, step 4 comprises step by step following:
Step by step 1, regulate the size of inversion unit voltage modulated ratio;
Step by step 2, regulate the magnitude of voltage of the DC bus capacitor of inversion unit: first adopt voltage close loop to control the average voltage of the magnitude of voltage of each inversion unit DC bus capacitor and all inversion unit DC bus capacitors to compare, the error signal of acquisition is used for the initial phase adjusting corresponding inversion unit, the magnitude of voltage of the DC bus capacitor of this inversion unit is changed, then according to the distribution of power proportions, inversion unit is redistributed, then regulate the output valve of each inversion unit; The current value producing needs and compensate is compared, for keeping magnitude of voltage and the compensation power loss of DC bus capacitor simultaneously by each inversion unit output current value and marker signal reference current value;
Step by step 3, compare the size of the magnitude of voltage of inversion unit DC bus capacitor and the average voltage of all inversion unit DC bus capacitors, when
time, return step by step 1; When
time, perform step by step 4; In formula,
the magnitude of voltage of each inversion unit DC bus capacitor,
for the mean value of all inversion unit DC capacitor voltages, ε is by testing the enough little parameter determined;
Step by step 4, process obtains critical equilibrium point, calculates
value, and with the actual measurement magnitude of voltage of voltage measuring point in electrical network
compare, when
time, return step by step 1; When
time, return step 4, continue to follow the tracks of the maximum power point of cascade multilevel photovoltaic grid-connected system; Wherein, σ is the enough little parameter determined by electric system standard.
6. the intelligent control method of a kind of cascade multilevel photovoltaic grid-connected system MPPT maximum power point tracking according to claim 5, is characterized in that, the value of parameter ε be 0.01, parameter σ value be 0.05.
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