CN114204590A

CN114204590A - Irradiation and temperature self-adaptive voltage optimization control method and ultra-long string photovoltaic system

Info

Publication number: CN114204590A
Application number: CN202010990022.2A
Authority: CN
Inventors: 宋悦; 陈泽熙
Original assignee: Guangzhou Zhongxu New Energy Co ltd
Current assignee: Guangzhou Zhongxu New Energy Co ltd
Priority date: 2020-09-18
Filing date: 2020-09-18
Publication date: 2022-03-18

Abstract

The invention discloses an irradiation and temperature self-adaptive voltage optimization control method and an ultra-long string photovoltaic system, and relates to the field of photovoltaic power generation, wherein an information acquisition module, a control module and a judgment module are arranged to adjust recommended reference duty ratios of optimizers, so that the photovoltaic string can be automatically balanced to exceed the voltage limit of an inverter at an extreme low temperature, and the output current of the optimizers exceeds the output current limit of the optimizer under extreme irradiation, so that the set number of components in the string is increased, the output current of the photovoltaic string is increased, the installed capacity is improved, the number of devices such as an inverter combiner box and the like with the same rated power is reduced, and the cost of a photovoltaic system is reduced; the output voltage of the photovoltaic string can be stabilized and is close to the maximum rated voltage of the inverter, and the number of components is increased by fully utilizing the step-down optimizer; the requirements on the response performance and the precision of the inverter and the power optimizer are not high, and the method is suitable for a large centralized power generation system with a large number of strings.

Description

Irradiation and temperature self-adaptive voltage optimization control method and ultra-long string photovoltaic system

Technical Field

The invention relates to the field of power generation, in particular to the field of photovoltaic power generation, and particularly relates to a method for irradiation and temperature adaptive voltage optimization control of a photovoltaic module-level or battery piece string-level power optimizer in a power generation system and an ultra-long string photovoltaic system.

Background

The photovoltaic power optimizer is a DC/DC converter connected to the photovoltaic module or to the substrings in the module, also with MPPT. On the principle of a circuit structure, the MPPT module carries out maximum power tracking and controls PWM to adjust duty ratio, and the photovoltaic module operates at a maximum power point. In a conventional photovoltaic module series structure, when power of a part of units is reduced due to shielding and the like, other units connected in series will also cause power loss due to the change of output voltage, that is, mismatch of a photovoltaic module string. In the series structure with the power optimizers, each optimizer independently tracks the maximum power and the duty ratio, so that the power mismatch caused by the external environment in the photovoltaic module is avoided.

According to the difference of the topology structure of the DC-DC conversion circuit, the DC-DC conversion circuit can be divided into three types: buck, Boost, and Buck-Boost. The Buck-type Buck DC/DC conversion circuit (which can also be a BOOST-Buck Buck type) is connected to the input end of the photovoltaic module and the output end of the inverter, and the input voltage U is connected to the output end of the inverter_in(i.e., power generation side output voltage) and output voltage U_outHas a relationship of U_out=U_inD (formula 1); input current I_in(i.e., the power generation side output current) and the output voltage I_outHas a relationship of_out=I_inD (equation 2). Wherein D is a duty ratio and can be adjusted between 0 and 1. In addition, after the optimizers are connected in series, an input direct current bus connected to the photovoltaic inverter is converted into AC alternating current by the photovoltaic inverter, and then the AC alternating current is boosted into a medium voltage of 10kv/20kv/35kv through a booster transformer and is connected to a power grid, or the AC alternating current is boosted to 110kv and above and is connected to a high-voltage grid. At present, the method for calculating the installation capacity of a photovoltaic string corresponding to an inverter is mainly that N is less than or equal to U_dcmax/{U_oc*[1+(t-25)*Kv]} (equation 3); wherein, U_dcmaxMaximum DC input voltage allowed for the inverter, U_ocThe open-circuit voltage of the photovoltaic module, t is the extreme low temperature under the working condition of the photovoltaic module, and Kv is the open-circuit voltage temperature coefficient of the photovoltaic module. For facilitating the selection of photovoltaic modules, the modules may be tested to obtain reference parameters, e.g. ground photovoltaic modulesStandard Test Conditions (STC): AM =1.5, 1000W/m²And 25 ℃ below zero. In the existing algorithm, the maximum value of the number of components in a group string is determined mainly by considering the extreme low temperature under the test condition, and the minimum value of the number of components in the group string is determined by determining the extreme high temperature under the working condition.

According to the principle, the power optimizer can track the maximum power point and can realize Buck type voltage reduction effect on the one hand, namely U_out=U_inD (formula 1) shows that it can reduce the actual output voltage of the photovoltaic module (the output voltage of the optimizer), increase the output current of the photovoltaic string, and increase the installed capacity, so that the number of devices such as the inverter combiner boxes with the same rated power is reduced, and the power generation capacity of the string is increased. In addition, as shown in FIG. 1, in the aspect of radiation dependence, taking a common silicon crystal photovoltaic component as an example, in the aspect of medium and high irradiance (more than or equal to 200W/m)²) In this case, the maximum power point voltage and the open circuit voltage do not change much with the change of irradiation. Therefore, in another aspect, the power optimizer has a maximum power point tracking feature, and the maximum power point voltage is about 0.83 times of the open circuit voltage, and thus the photovoltaic module with the power optimizer can not operate in the interval from the maximum power point voltage to the open circuit voltage, so that the module voltage for calculating the capacity of the photovoltaic string can be reduced, and the string power generation capacity can be further improved.

In existing photovoltaic power generation systems, the optimizer is a fixed reference duty cycle and the output voltage of the optimizer is configured by an inverter. When the assembly is unobstructed, each optimizer runs near the reference duty cycle with the actual duty cycle D varying within ± 3%. In the exemplary hypothetical case, I is at the limit irradiation condition of a certain environment_out=1.11*I_mpThen the duty cycle of the optimizer operates in the range of 90% ± 3% according to equation 2, and the voltage V is output accordingly_out=0.9V_pv. And the optimizer can track the maximum power point, then V in equation 3_ocCan adopt maximum power point voltage V_m. Thus, from equation 3, the existing method for computing components in a string is N = U_dcmax/{0.9*0.83V_oc*[1+(t-25)*Kv]I.e. V_out=0.9*0.83*V_oc=0.747V_ocThus, an assembly with an optimizer can therefore increase the photovoltaic module installation capacity by about 30% with the Buck-type optimizer under the existing method of fixed reference duty cycle. If the reference duty ratio is 0.8, the voltage V is correspondingly output_out=0.8Vpv, the component calculation method in the existing group string is N = U_dcmax/{0.8*0.83V_oc*[1+(t-25)*Kv]I.e. V_out=0.8*0.83*V_oc=0.664V_ocI.e. a 50% capacity increase. When the reference duty ratio is fixed to 0.8 and the string capacity is further increased, the reference duty ratio is increased from I_out=1.25I_mpIt can be seen that in the case of extreme irradiation, I_outWill exceed the rated maximum output voltage I of the optimizer_om. Currently, the maximum output current of the main power optimizer is about 1.06 times the maximum input current.

A drawback of the prior art solutions is that the reference duty cycle of the optimizer is limited to the maximum output current I of the optimizer if it is considered_omThe mounting capacity of the string is reduced by 20%, and the maximum output current I is handled in consideration of the low probability of the extreme environment_omThe life of the system for long-term operation is reduced. Meanwhile, the exceeding of the maximum output current mainly occurs 3-4 hours before and after noon in one day, and other time periods are far lower than the I under the STC test condition_mp(ii) a In the whole year, when the limit temperature appears, the irradiation is different from the STC test condition, for example, the noon low temperature in winter is accompanied by the irradiation of 1000W/m lower than the test condition²Such as the extreme irradiation of positive and negative in summer, will be accompanied by high temperature and make U_ocDecreases under negative temperature factors. In addition, these extremes may force the power optimizer output to become unstable at a limit voltage (or current), causing a surge on the inverter. If the duty ratio of the optimizer is independently adjusted in real time according to the running states of real-time voltage, current, temperature and the like, the corresponding efficiency of very accurate detection and communication is needed, and the method cannot be applied to the condition that the number of photovoltaic modules and photovoltaic string in a large photovoltaic power station is large.

Disclosure of Invention

The invention provides an irradiation and temperature self-adaptive voltage optimization control method and an ultra-long string photovoltaic system, aiming at solving the contradiction between the maximum current limit of an optimizer and the requirement of increasing the string capacity by utilizing the optimizer, increasing the number of series components of each component string and the string photovoltaic installed capacity, reducing the power consumption cost (LCOE) of the photovoltaic system, and reducing the impact of string voltage (or current) on the system under the limit environmental condition.

Particularly, the photovoltaic power generation system is mainly applied to the ground, the water surface and a large industrial and commercial roof scene, and has the characteristics of single environment, basically consistent orientation of photovoltaic arrays and consistent number of components of each photovoltaic group string.

In order to achieve the purpose, the invention adopts the following technical scheme:

in one aspect, the invention provides an irradiation and temperature adaptive voltage optimization controlled ultra-long string photovoltaic system, which comprises a photovoltaic power generation unit, an optimizer, an inverter and a control module; the input end of the optimizer is connected to the output end of the photovoltaic power generation unit and tracks the maximum power point of the photovoltaic power generation unit, the output ends of the optimizer are connected in series to form a series connection body, the output end of the series connection body is connected to a direct current bus of the inverter, and the alternating current side of the inverter is connected to a power grid; the direct current bus of the inverter (30) recommends reference input voltage, the control module (52) can obtain operation information of the optimizer (40) and the inverter (30), the control module (52) recommends reference duty ratio for each series connection body (20) according to the real-time operation information of the optimizer (40) and by referring to the direct current bus reference input voltage, and the optimizer (40) adjusts actual duty ratio in a floating range of the recommended reference duty ratio.

Specifically, the method further comprises an information acquisition module (51) and a judgment module (50), wherein the judgment module (50) compares the difference between the operation information of the inverter (30) and the currently recommended direct-current bus reference input voltage, judges whether the recommended reference duty ratio is adjusted correspondingly or not, and the information acquisition module (51) acquires the operation information of the optimizer (40) and the inverter (30).

In the above ultra-long string photovoltaic system, preferably, the information acquisition module may obtain an input voltage of a maximum power point of each optimizer in a string, and the average input voltage is obtained by processing of the control module; the control module obtains the reference output voltage of the optimizer according to the reference input voltage of the direct current bus and the number processing of the optimizers, and the control module obtains the recommended duty ratio according to the average input voltage of the optimizer and the reference output voltage of the optimizer.

In the above-mentioned super-long string photovoltaic system, preferably, the optimizer is a Buck-type or Buck-Boost-type Buck-Boost DC/DC conversion circuit, the inverter is a Boost-free single-stage DC/AC conversion circuit or a Boost-Boost two-stage DC/AC conversion circuit, and the control module obtains the recommended duty ratio according to a division value of the average input voltage of the optimizer and the reference output voltage of the optimizer.

In the above ultra-long string photovoltaic system, preferably, the information acquisition module may obtain input currents of the optimizers in the string, and the recommended duty ratio set by the determination module may make a ratio of an actual input current of the optimizers to the recommended duty ratio smaller than a rated maximum output current of the optimizers; the judgment module sets a recommendable maximum threshold of a recommended duty ratio according to the ratio of the input current to the rated output current in the extreme environment.

In the above ultra-long string photovoltaic system, preferably, the information acquisition module may acquire an actual input voltage of the dc bus of the inverter, the determination module compares the actual input voltage of the dc bus with a currently recommended reference input voltage of the dc bus and makes a determination, if a difference between the actual input voltage of the dc bus and the currently recommended reference input voltage of the dc bus exceeds a set ratio, the reference input voltage recommended to the dc bus of the inverter is adjusted, and a reference duty ratio recommended to each of the string power optimizers is adjusted accordingly until the difference between the actual input voltage of the dc bus and the currently recommended reference input voltage of the dc bus is within the set ratio. At a reference duty cycle D_refAnd judging the voltage change of the direct current bus, wherein in one aspect, the set proportion of the judgment module to the change judgment of the inverter is equivalent to the set floating range of the power optimization module which operates according to the recommended duty ratio. Specifically, the setting proportion of the change judgment by the judgment module is in a range of 2% to 8%, and the setting mode of the percentage depends on the actual layout mode and the layout scene of the photovoltaic power generation system. In the same wayThe mismatch conditions showing consistency in each photovoltaic module in the scene are more, and the local mismatch conditions such as local foreign matter shielding are less, so that the value of the set proportion can be lower, such as 2% to 4%. Otherwise, the value of the set ratio is higher.

In the above ultra-long string photovoltaic system, preferably, the switching frequency of the operation of the power device of the optimizer is higher than the switching frequency of the operation of the switching device of the inverter; in the operation period of the inverter, if consistency mismatch exists between series bodies, the inverter tracks the maximum power point of the parallel series bodies within a set proportion so as to adjust the voltage of the direct current bus, and an optimizer in each series body adjusts the actual duty ratio within the floating range of the reference duty ratio along with the adjustment of the actual voltage of the direct current bus; in the running period of the optimizers, if the non-uniformity mismatch exists in the serial body, the voltage of the direct current bus is not changed, and the optimizers in the serial body with the non-uniformity mismatch maintain the output current and adjust the actual duty ratio consistently according to the floating range of the reference duty ratio.

In the above ultra-long string photovoltaic system, preferably, the information acquisition module acquires a grid-connected point voltage UT at an ac side of the photovoltaic inverter, and the determination module compares the grid-connected point voltage UT with a power frequency voltage, determines that the photovoltaic inverter is in a normal operating mode or a high-voltage operating mode, and recommends a corresponding initial reference input voltage for the inverter to input a dc bus according to different operating modes.

In the above ultra-long string photovoltaic system, preferably, the photovoltaic power generation unit is a photovoltaic module, or a serial-parallel structure of a part of photovoltaic cells in a photovoltaic module; two or more of the series bodies are connected in parallel with each other and output ends thereof are connected to input ends of inverters; the total capacity of the photovoltaic power generation units of all the serial bodies is equivalent to the installation relative position; the capacities of the photovoltaic power generation units connected with the optimizers are equivalent; each photovoltaic power generation unit in the series connection body is installed in the vertical direction, and the photovoltaic power generation units are connected in series by photovoltaic battery pieces in the installation transverse direction. In a photovoltaic power generation system, partial mismatch can be divided into conventional mismatch by allocating photovoltaic cells, photovoltaic modules and some structural changes of the photovoltaic modules, so that the unconventional mismatch is reduced, the judgment value is further reduced, and the system is more stable, efficient and low in cost. The power failure of unconventional mismatch, such as bird droppings, flying birds and individual components inside the photovoltaic string, is avoided, the mismatch ratio of the component levels is not too high, and the number of the components inside the photovoltaic string is not influenced to exceed 3%.

In another aspect, the invention provides a method for irradiation and temperature adaptive voltage optimization control, which is applied to a grid-connected photovoltaic power generation system, wherein the grid-connected photovoltaic power generation system comprises a photovoltaic power generation unit, an optimizer and an inverter; the input end of the optimizer is connected to the output end of the photovoltaic power generation unit and tracks the maximum power point of the photovoltaic power generation unit, the output ends of the optimizer are connected in series to form a series connection body, and the output end of the series connection body is connected to a direct current bus of the inverter, and the method comprises the following steps: obtaining operation information of an optimizer and an inverter, and recommending a reference input voltage for a direct current bus; recommending reference duty ratios for all series bodies according to the operation information of the optimizer and by referring to the reference input voltage of the direct-current bus; the optimizer adjusts the actual duty cycle within the floating range of the recommended reference duty cycle; and comparing the difference between the operation information of the inverter and the reference input voltage of the current recommended direct-current bus, and judging whether to correspondingly adjust the recommended reference duty ratio.

The method is preferably applied to a grid-connected photovoltaic power generation system, specifically, the operation frequency of the optimizer is higher than that of an inverter, the optimizer is a Buck-type Buck or Buck-Boost-type Buck-Boost DC/DC conversion circuit, the inverter is a single-stage DC/AC conversion circuit without Boost voltage boosting or a two-stage DC/AC conversion circuit with Boost voltage boosting, and the method includes the specific steps:

obtaining a grid-connected point voltage UT at an alternating current side of the inverter, comparing and judging the grid-connected point voltage UT with a grid-connected point power frequency reference voltage, and judging that the inverter is in a normal working mode if UT is less than or equal to 1.1 p.u.; if UT is>1.1p.u., then the inverter is judged to be in a high-voltage working mode, and the inverter is correspondingly set according to different working modesInitial U of DC bus_dcref；

When in the normal working mode, setting the initial DC bus reference input voltage U_dcrefAnd each optimizer in the tandem sets a matched reference duty cycle D_refWherein the duty ratio D is referenced_refReference input voltage U from DC bus_dcrefSum of input voltages to optimizers in series ∑ U_inThe division value of (a); the obtained actual input voltage U_dcAnd a reference input voltage U_dcrefAnd (4) comparing and judging: if the direct current bus is | (U)_dc-U_dcref)/U_dcrefIf | exceeds the set proportion, readjusting U_dcrefAnd is provided with D_refUp to U_dcAnd U_dcrefSatisfy | (U)_dc-U_dcref)/U_dcrefThe ratio is not more than the set ratio; if the direct current bus is | (U)_dc-U_dcref)/U_dcrefIf I does not exceed the set proportion, the current reference input voltage U is used_dcrefAnd a reference duty cycle D_refRunning until the inverter tracks the maximum power point and the running period changes U_dcOr the AC side turbulence of the inverter is fed back to the DC bus side to change U_dcAnd make | (U)_dc-U_dcref)/U_dcrefI exceeds a set proportion;

in each operation period of the inverter, if consistency mismatch exists between serial bodies, the inverter performs U operation_dcrefThe actual input voltage U of the direct current bus for tracking the maximum power point in the set proportion_dc(ii) a Following the actual input voltage U_dcOptimizers in each series at a reference duty cycle D_refThe actual duty ratio D is adjusted within the floating range of the load to balance the consistency mismatch among all series bodies;

in each operation period of the optimizer, if non-uniformity mismatch in the series connection exists, the direct current bus voltage U_dcInvariably, the output current is maintained consistent by each optimizer in the non-uniformly mismatched serial body according to the reference duty ratio D_refThe actual duty ratio D is adjusted within the floating range of the series to balance the non-uniform mismatch inside the series;

when operating at high voltageIn mode, bus reference U_dcrefArranged outside the maximum power point voltage tracking range of the inverter by adjusting the reference input voltage U_dcrefRespective optimizers in the tandem set matching reference duty cycles D_refUntil the direct current bus (U)_dc-U_dcref)/U_dcrefL does not exceed a set proportion;

the input current of the optimizer is obtained, the recommended duty ratio is set to meet the requirement, and the ratio of the real-time input current of the optimizer to the recommended duty ratio is smaller than the rated maximum output current of the optimizer.

Compared with the prior art, the invention has the following beneficial effects:

according to the power generation system, the information acquisition module, the control module and the judgment module are arranged, so that the recommended reference duty ratio of each optimizer is adjusted according to the current operation states of the optimizers and the inverters under the reference input voltage of the direct current bus of the inverter according to the actual irradiation and temperature change, the photovoltaic string can be automatically balanced to exceed the voltage limit of the inverter at the extremely low temperature in the setting process of the string, the output current of the optimizers exceeds the output current limit of the optimizers under the extreme irradiation, the setting number of components in the string is increased, the output current of the photovoltaic string is increased, the installed capacity is improved, the number of devices such as inverter combiner boxes with the same rated power is reduced, and the cost of the photovoltaic system is reduced; in addition, the photovoltaic power generation system can stabilize the output voltage of the photovoltaic string and approach the maximum rated voltage of the inverter, fully utilizes the step-down optimizer to increase the number of components, has low requirements on the response performance and the precision of the inverter and the power optimizer, and is suitable for large-scale centralized power generation systems with large string numbers.

The invention will be further described with reference to the accompanying drawings.

Drawings

FIG. 1 is a schematic view of photovoltaic electrical parameter characterization;

FIG. 2 is a schematic diagram of a circuit structure of an ultra-long string photovoltaic system according to the present invention;

FIG. 3 is a schematic view of an irradiation and voltage adaptation flow of the optimized voltage control method of the present invention;

FIG. 4 is a schematic diagram illustrating a working state determination process of the optimized voltage control method according to the present invention;

FIG. 5 is a schematic flow chart of the optimized voltage control method of the present invention in a normal operation state;

fig. 6 is a schematic flow chart of the optimized voltage control method in the high voltage operating state according to the present invention.

Reference numerals: 10. a photovoltaic module; 20. a photovoltaic string; 30. an inverter; 40. an optimizer; 50. a judgment module; 51. an information acquisition module; 52. a control module; 60. a step-up transformer; 70. and (4) a power grid.

Detailed Description

To better illustrate the objects, technical solutions and advantages of the present invention, the following detailed description of the embodiments of the present invention is provided with reference to the accompanying drawings and examples. The following examples are intended to illustrate the invention, but are not intended to limit the scope of the invention.

As shown in fig. 2, the photovoltaic power generation system for optimizing voltage control according to the present invention includes a photovoltaic power generation unit, an optimizer 40, an inverter 30, a judgment module 50, an information collection module 51, and a control module 52; specifically, the number of the optimizers 40 is multiple, the number of the photovoltaic power generation units is the number of the photovoltaic modules 10 and is equal to that of the optimizers 40, referring to fig. 1, N photovoltaic modules 10 numbered from 10-1 to 10-N are arranged in the photovoltaic string 20, the output end of each photovoltaic module 10 is connected with the optimizers 40, and the N optimizers 40 numbered from 40-1 to 40-N are connected in series with each other to form the photovoltaic string 20. The input end of each optimizer 40 is connected to a photovoltaic power generation unit, and each optimizer 40 has a maximum power tracking module, i.e., MPPT module, suitable for the power optimizer 40 and can track the maximum power point of the photovoltaic module 10 through the MPPT module. The outputs of the plurality of optimizers 40 are connected in series to form a series, and the series and the photovoltaic modules 10 connected thereto may be referred to as a photovoltaic string 20. The plurality of photovoltaic strings 20 are connected to a dc bus of the inverter 30. Referring to fig. 2, the photovoltaic power generation system has M photovoltaic strings 20, which are numbered 20-1 to 20-M, and the photovoltaic strings 20 are connected in parallel with each other to form a photovoltaic module 10 array, are connected to a dc bus, and are connected to an input terminal of a photovoltaic inverter 30 by the dc bus. The inverter 30 has a maximum power tracking module, i.e., MPPT module, adapted to the inverter 30, and can track a maximum power point of the dc bus through the MPPT module. A step-up transformer 60 is connected to the ac side of the inverter 30, and the ac point is boosted and then grid-connected to the grid 70.

Referring to fig. 2, the photovoltaic power generation system includes a determination module 50, an information collection module 51, and a control module 52. The information acquisition module 51 is used for detecting and acquiring information of the direct current side and the alternating current side of the inverter 30 and information of the output end and the output end of the optimizer 40, providing judgment parameters for the judgment module 50 and providing control parameters for the control module 52; the judging module 50 is used for judging and selecting the running state of the photovoltaic power generation system according to the sensing parameters; the control module 52 performs calculation processing according to the information acquired by the information acquisition module 51, and controls the operation of the optimizer 40 and the inverter 30 according to the result of the judgment module 50. On one hand, the information acquisition module 51 is coupled to the input end and the output end of each power optimization module, or is connected to the MPPT module of the power optimization module through an interface, and acquires the input voltage and the input current of each power optimization module in the photovoltaic string 20 in an information sharing manner. On the other hand, the input voltage of the inverter 30 may be detected and acquired by a voltage sensor coupled to the dc bus to which each of the photovoltaic string 20 is connected. Furthermore, the number of power optimization modules in the photovoltaic string 20 is obtained by an input method when the power generation system is installed. The control module 52 may be a device that performs parametric processing and control communication with the power optimization modules and is connected to each power optimization module. The judgment module 50, the information acquisition module 51 and the main control module are set in a centralized management system of the photovoltaic power generation system, and may be an industrial PC with an interface card and configured with the photovoltaic management system, and the centralized management system is externally or internally arranged in the dc combiner box and the inverter 30.

In this embodiment, the information collecting module 51 obtains the input current I of each optimizer 40 by connecting to it_inInput voltage U_inOutput current I_outAnd U_outEtc. by coupling toThe grid 70 grid-connected point obtains a grid-connected point voltage UT, and obtains a direct current bus voltage U by coupling to a direct current bus_dcI.e. the input voltage of inverter 30.

Reference duty cycle D_refIs that the information acquisition module 51 acquires U_in-1，U_in-2,U_in-3,…,U_in-nAnd U is calculated by the control module 52_in-1+U_in-2+U_in-3+…+U_in-nThe average value of the input voltage of the optimizer 40 obtained by/n is calculated by the control module 52 on the DC bus U_dcThe output reference voltage, i.e. U, assigned to each optimizer 40 in the string of groups_dcAnd/n. Since the optimizer 40 is a Buck Buck DC/DC conversion circuit, the reference duty ratio D_refIs obtained by dividing the output reference voltage by the average value of the input voltage. The control module 52 will reference the duty cycle D by establishing communication with the respective optimizers 40_refRecommended into the optimizer 40. In other embodiments, the reference duty cycle D_refOr may be the reference input voltage U of the DC bus_dcrefAnd sum of input voltages of the optimizers 40 ∑ U_inThe ratio of | n. The optimizer 40 obtains the reference duty cycle D_refThe actual duty cycle D will be chosen within a floating range, e.g. ± 5%. Likewise, it is understood that the actual duty cycle D takes the value D_ref-5%≤D≤D_ref+ 5%. It will be appreciated that the adjustment frequency of the optimizer 40 is faster, and that the optional non-responsive reference duty cycle, which may exceed D, may occur when the optimizer 40 determines that the current electrical parameter change rate is faster_refThe floating range adjusts the actual duty cycle.

In the aspect of recommending the input voltage of the dc bus, the determining module 50 specifically compares and determines the output voltage UT of the grid-connected point with the grid-connected point power frequency reference voltage, and if UT is less than or equal to 1.1p.u., determines that the inverter 30 is in the normal operating mode; if UT is>1.1p.u., it is determined that the inverter 30 is in the high voltage operation mode. Setting the initial U of the DC bus according to different operating modes_dcrefAnd sets a matching reference duty cycle D within each optimizer 40 in the tandem_ref. If the power frequency reference voltage is 800V, the power frequency reference voltage is initially set in a normal working modeU of (1)_dcref1.414 × 1.1 × p.u., about 1250V; high voltage operating mode, initial U_dcref1.414 × 1.2 × p.u., about 1400V. When inverter 30 is in the normal operation mode, initial reference input voltage U of the normal operation mode is set_dcrefThe judging module 50 is used for judging the input voltage U according to the reference_dcrefAnd the actual DC bus voltage U_dcAnd comparing and judging: if the direct current bus is | (U)_dc-U_dcref)/U_dcrefIf | exceeds the set proportion, increasing or decreasing U_dcrefAnd recommends D anew accordingly_refIf the direct current bus is | (U)_dc-U_dcref)/U_dcrefIf the I does not exceed the set proportion, maintaining the currently recommended U_dcrefAnd D_refAnd (5) operating. Wherein, in one aspect, the set ratio is 5%. Wherein, in the operation period of the relative optimizer 40, the change of the irradiation and the temperature can be regarded as constant, and the operation of the MPPT module of the inverter 30 can be regarded as U of the maximum power point_dcInvariant, but AC-side perturbation pairs U_dcIs bursty and must be treated as U_dcAre variable. The difference between the dc side and the ac side of the inverter 30 can be balanced by the decision block 50, on the one hand to balance the grid 70 surge with the optimizer 40 and on the other hand to maintain the inverter 30 input voltage stable.

As shown in fig. 3 to 6, the photovoltaic power generation system with optimized voltage control has similar features as the above photovoltaic power generation system with optimized voltage control, and is a method for optimizing voltage control, which is schematically applied to a photovoltaic power generation system with an inverter 30 having a rated voltage of 1500V, and the method includes the steps of: detecting and acquiring current DC bus voltage U_dcObtaining sum of input voltages of optimizers 40 in the tandem_inN, obtaining the current output current I of the tandem_outInformation on the dc side and/or the ac side such as the grid-connected point voltage UT on the ac side of the inverter 30 is acquired. (1) Comparing and judging according to the UT and the grid-connected point power frequency reference voltage, and if the UT is less than or equal to 1.1p.u., judging that the inverter 30 is in a normal working mode (1 a); if UT is>1.1p.u., then it is determined that the inverter 30 is in the high voltage operating mode (1 b), and the initial dc bus is set accordingly according to the different operating modesU_dcref。

And (3) carrying out different processing modes on the judgment result: (1a) if the judgment result is that the current state is in the normal working mode, setting the initial direct current bus reference input voltage U_dcref=1250V, then pass U_dcref/∑U_inEach optimizer 40 setting | n in the series a matching reference duty cycle D_ref. (2) According to the actual input voltage U_dcAnd a reference input voltage U_dcrefAnd (4) comparing and judging: if the direct current bus is | (U)_dc-U_dcref)/U_dcrefIf | exceeds 5% (2 a), U is readjusted_dcrefAnd is provided with D_ref(ii) a And re-detecting the DC bus U_dcAnd entering judgment (2) until (U)_dc-U_dcref)/U_dcrefL is not more than 5%; if the direct current bus is | (U)_dc-U_dcref)/U_dcrefI does not exceed 5% (2 b) with the current reference input voltage U_dcrefAnd a reference duty cycle D_refAnd (5) operating. When the determination is at (2 b), the inverter 30MPPT tracks the maximum power point and adjusts the dc bus voltage U at each stage_dcAnd judging the running state of the photovoltaic string 20: if each optimizer 40 tandem output has a dU_dc/dt>Setting the value, the consistency mismatch of each photovoltaic string 20 can be judged, and the optimizer 40 of each photovoltaic string 20 can be used for judging the consistency mismatch according to D_refSetting an actual duty ratio within a range of +/-5% to enable the voltage of the output end of each photovoltaic string 20 to be consistent with the maximum power point voltage of the inverter 30, and balancing the mismatch; if all the output ends of the serial bodies of the partial optimizers 40 have dU_dc/dt>Setting value, it can be determined as non-uniformity mismatch of some photovoltaic modules 10, and maintaining the maximum power point voltage of the inverter 30, and passing through the optimizer 40 of the mismatched photovoltaic strings 20 at D_refAutomatically adjusting the duty ratio within the range of +/-5% to balance the mismatch; if dU_dcIf dt is less than or equal to the set value, the judgment (2) is carried out again to detect whether the system fluctuates. (1b) If the judgment result is that the direct current bus is currently in the high-voltage working mode, setting an initial direct current bus reference input voltage U_dcrefIf =1400V, pass U_dcref/∑U_inEach of | n in the concatemerThe optimizer 40 sets a matched reference duty cycle D_ref. At this time, the maximum power tracking of the inverter 30 is disabled, and the system performs the judgment (2) to make | (U)_dc-U_dcref)/U_dcrefThe | -is not more than 5%.

And thus can be analyzed exemplarily. Assuming that the grid 70 is operating steadily, the dc bus reference input voltage of the inverter 30 can be considered as being steady at 1250V, i.e., around 1.414 times the ac effective voltage 800V taking into account the ac voltage peak.

The photovoltaic module 10 is at low solar irradiance during the pre-and post-sunrise periods, i.e., during the period of the day when the temperature of the photovoltaic module 10 is at its lowest, and for a period of time after sunrise (Ir < 200W/m)²) In this phase, the output working current of the photovoltaic module 10 is very small, and the problem that the output current of the optimizer 40 exceeds the limit is not considered, and is less than 0.2I_mp(the STC test shows that the working current of the module is lower because the temperature of the photovoltaic module 10 is lower, and the maximum power point voltage of the module is close to U according to the voltage negative temperature characteristic_mpTherefore, a lower reference duty ratio can be adopted at this stage, such as 0.66, the system starting requirement can be met, and the early starting and early power generation of the inverter 30 can be realized.

With increasing solar radiation, e.g. 200W/m²≤Ir≤850 W/m²At this stage, the working current of the photovoltaic module 10 is increased, i.e. 0.2-0.85 times I_mpAnd the battery temperature gradually rises, the maximum power point voltage of the component approaches or is larger than U_mpHowever, the output current of the optimizer 40 is still far from the current limit of the optimizer 40, and the maximum power point voltage and the dc bus voltage U can be tracked by the inverter 30 at this stage_dcIs continuously monitored and determined and the reference duty cycle D is recommenced for the optimizer 40_refAnd is sequentially increased between 0.66 and 0.78, the maximum power point voltage of the photovoltaic module 10 will increase as the irradiation increases, i.e., U_in-1+U_in-2+U_in-3+…+U_in-nAfter increasing, the DC bus voltage U can be finally enabled_dcAnd a recommended voltage U_dcrefAre close to each other.

At the position ofDuring several hours before and after noon, the solar radiation will be in high illumination stage, such as Ir > 850W/m²In summer limit days of the year, the solar radiation may reach 1150W/m². The working current component of the photovoltaic component 10 increases at this stage, namely 0.85-1.15 times Imp. However, as the irradiation is increased, the temperature of the battery will increase to over 65 ℃, and the actual U is determined according to the negative temperature characteristic of the voltage_in-1+U_in-2+U_in-3+…+U_in-nWill be reduced and it is possible to make the voltage limit of the inverter 30 input dc bus not exceeded also in the case of duty cycles taking a higher value. Thus, by making continuous monitoring and decisions and re-recommending the reference duty cycle D to the optimizer 40_refSuch as 0.8-0.95 or more. As the reference duty cycle increases, the optimizer 40 output voltage Iout will be controlled to be within the optimizer 40 output current limit. Similarly, before and after sunset, it has a similar stage to sunrise, and is not described herein again.

In the illustrative embodiment, the photovoltaic module 10 is used in a photovoltaic power generation system, and the operating parameters of the photovoltaic module 10 are that the module is irradiated by 1000W/m at the temperature of 25 DEG C²And under the STC photovoltaic test of an AM1.5 spectrum, the maximum power point output current Im of the module is 13A, the maximum power output voltage Um of the module is 41V, and the open-circuit voltage is 49.4V. The BUCK-type photovoltaic power optimizer 40 adopted by the photovoltaic power generation system has the parameters that the input current limit is 15A and the output current limit is 16A. The photovoltaic power generation system also adopts a photovoltaic inverter 30, the maximum input voltage is 1500V, and the MPPT voltage regulation range is fully loaded. The application scene is Qinghai gelmu, and the environmental data of extreme high temperature, extreme low temperature and the like under high irradiance or low irradiance can be obtained, wherein the extreme low temperature t of the environment is-25 ℃, the extreme high temperature is 65 ℃, and the extreme irradiation is 1100W/m²The voltage temperature coefficient is-0.3%/DEG C, the influence of different voltage control methods on the installation quantity of the components is measured, the same environmental data and other conditions are adopted for comparison, and the values are only convenient to understand and are not limited specifically.

In the case of the components of the conventional unpowered optimizer 40, by equation 3, N ≦ { U ≦_dcmax/{U_oc*[1+(t-25)*Kv]Get (i.e. {1500/{49.4 [ -1-0.3%. - (-25-25)]N ≦ 26.4, the number N1 of photovoltaic modules 10 is 26.

In a conventional voltage control method with a power optimizer 40 and fixed with reference to the duty cycle. If the reference duty ratio is fixed to 0.8, N2= N1/(0.8 × 0.83) =39 due to the maximum power point tracking of the optimizer 40 and the voltage reduction effect of the Buck dc converter circuit. However, extreme irradiation such as 1150W/m is considered²Then Iout =1.15 × 13A/0.8=18.7A, the current will exceed the limit of 16A, thus requiring a reduction of the device capacity by 15%, i.e. the I of the selected photovoltaic device 10_mpThe reduction is 15%. If the reference duty ratio is 0.9, there is I_outI =1.15 × 13A/0.9=16.6, plus the actual duty cycle adjustment of the optimizer 40, I can be maintained_moWithin 16A of the limit. Therefore, when the reference duty ratio is 0.9, the reference duty ratio is defined by N2= N1/(0.93 × 0.83) = 33.6. Therefore, N2 is actually selected as 33 blocks in the aggregate.

The reference duty cycle varies as dictated by the voltage control scheme according to the present invention, i.e., as a function of the actual operating conditions of the system. Under extreme irradiance, the practical optimizer 40 inputs the current I_mpIf it exceeds 1.15 times I_mpAnd I_outThe reference duty cycle under the limit may take 0.93. In the 39 block scheme, the output voltage across the string 20 would be 39 x 41 x 0.93 would exceed the 1500 rated voltage. However, the proposal of the invention recommends the reference duty ratio according to the actual voltage situation, and the temperature of the battery will rise along with the reference duty ratio under the extreme irradiation of the power generation system, namely the actual output voltage is 39 × 41 × 0.93 × 1-0.3% (65-25)]Will be around 1300. Considering that the actual irradiation is less than 1000W/m of STC test condition at extremely low temperature²Considering that the actual temperature under extreme irradiation will be higher than 25 ℃ under the STC test condition, the selected component of the photovoltaic string 20 may be more than 39 under the voltage control scheme of the present invention.

In a conventional photovoltaic system without the power optimizer 40, a string of pv strings 20 has 26 modules, and the operating states of the pv modules 10 and the pv strings 20 are as follows, and taking the irradiation and temperature conditions at different time points of the day as an example, the operating states of the pv modules 10, the power optimizer 40 and the pv strings 20 are as shown in table 1 below.

Serial number	Solar radiation (W/m2)	Temperature of Battery (. degree. C.)	Maximum power output current of battery (A)	Group string working voltage (V)	Group open circuit voltage (V)
						1	200	-15	2.60	1236	1446
2	400	0	5.20	1172	1371
						3	850	30	11.05	1044	1221
4	1000	55	13.00	938	1097
						5	1100	65	14.30	895	1047

In the photovoltaic system under the control method of the conventional optimizer 40, the reference duty ratio is fixed to be 0.8, the number of the series-connected modules is 33, and the operating states of the photovoltaic module 10, the power optimizer 40 and the photovoltaic string 20 are as shown in table 2 below, taking the irradiation and temperature conditions at different time points in one day as an example.

Sequence of steps Number (C)	Solar radiation (W/m2)	Temperature of battery (℃)	Power optimizer 40BUCK type Circuit duty cycle D	Maximum power output of battery Current (A)	Optimizer 40 maximum power Output current (A)	Group voltage (V)
							1	200	-15	0.80	2.6	3.25	1483
2	400	0	0.80	5.2	6.5	1407
							3	850	30	0.80	11.05	13.81	1253
4	1000	55	0.80	13.0	16.25	1125
							5	1100	65	0.80	14.3	17.87	1074

In the photovoltaic system under the control method of the optimizer 40 of the present invention: the reference duty cycle varies with the current system operating conditions, the number of series-connected modules is 39, and the operating conditions of the photovoltaic module 10, the power optimizer 40 and the photovoltaic string 20 are shown in table 3 below, taking the irradiation and temperature conditions at different time points as an example.

Sequence of steps Number (C)	Solar radiation (W/m2)	Temperature of battery (℃)	Power optimizer 40BUCK type Circuit duty cycle D	Maximum power output of battery Current (A)	Optimizer 40 maximum power Output current (A)	Group voltage (V)
							1	200	-15	0.66	2.60	3.90	1225
2	400	0	0.70	5.20	7.40	1231
							3	850	30	0.78	11.05	14.10	1222
4	1000	55	0.87	13.00	14.94	1224
							5	1100	65	0.92	14.30	15.54	1235

The advantages of the solution according to the invention are seen from tables 1 to 3. In the conventional scheme of the unpowered optimizer 40, as shown in table 1, it is apparent that in the scheme, the number of components in a string is small, and only 67% of the capacity of the scheme exists, and meanwhile, the conventional components are prone to mismatch, which results in power loss; moreover, as the load of the inverter 30 changes, the grid disconnection is very easy to happen, the fluctuation of the working voltage is large along with the day, and the instability of the power inversion process is increased. In the conventional power optimization method and system, as shown in table 2, in the states of

serial numbers

1 and 2, the string voltage exceeds the adjustment range of the photovoltaic inverter 30; under the state of serial numbers 4 and 5, the medium current exceeds the rated range of the optimizer 40, and under the state of serial number 5, when the power grid 70 is abnormal, the alternating current output of the photovoltaic inverter 30 is required to be overloaded, and the connection with the power grid 70 is disconnected due to the fact that the voltage of the group string is too low, so that the high-voltage ride-through cannot be completed. In the power optimization method and system of the scheme, as shown in table 3, under various conditions of a day, such as string and mismatch, mismatch and irradiation and temperature change, the string voltage is maintained between 1221V and 1231V, and the fluctuation range is within 0.8%. Under the condition of facing extreme environment and the mismatch of component levels, the current and the voltage can not exceed the rated range of devices and equipment; and the number of components in the scheme is higher than that in the traditional system, and the high voltage of a grid-connected point facing an alternating current side can be stably operated without grid disconnection.

In addition to increasing the number of components, the present embodiment has an advantage that the determining unit recommends setting the reference voltage of the dc bus of the inverter 30 and the reference duty ratio of the corresponding power optimization module according to the system conversion state, and adjusts the actual output voltage of the serial body of the optimizer 40 by using the reference duty ratio, that is, the actual voltage of the dc bus of the inverter 30 matches the ideal reference input voltage, so that each optimizer 40 has a floating adjustment space according to the operation state thereof; on one hand, the method can adapt to the mismatch condition which is uniformly generated in each series connection body, and the actual duty ratio is uniformly selected to enable the direct current bus to obtain the actual voltage capable of balancing the mismatch; on the other hand, the local non-uniformity mismatch condition can be adjusted in a self-adaptive mode, and the actual duty ratio can be further selected by maintaining the bus voltage unchanged and matching the partial optimizer 40 with the series body current; generally, the dc bus voltage of the inverter 30 is stabilized within a variation range of a very small amplitude, and the voltage impact of the disturbance feedback of the power grid 70 to the dc side can be balanced, so that the high voltage ride through requirement can be satisfied; and the inverter 30 is maintained in a high input voltage state, the alternating current output voltage can be improved, the alternating current line loss of the inverter 30, the step-up transformer 60, a cable and the like is reduced, the requirements on the response performance and the precision of the inverter 30 and the power optimizer 40 are not high, and the method is suitable for a large-scale centralized power generation system with a large number of strings.

The foregoing embodiments have been described primarily for the purposes of illustrating the general principles, and features and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed.

Claims

1. An irradiation and temperature adaptive voltage optimization controlled ultra-long string photovoltaic system is characterized by comprising a photovoltaic power generation unit (10), an optimizer (40), an inverter (30) and a control module (52); the input end of the optimizer (40) is connected to the output end of the photovoltaic power generation unit (10) and tracks the maximum power point of the photovoltaic power generation unit, the output ends of the optimizer (40) are connected in series to form a series body (20), the output end of the series body (20) is connected to a direct current bus of the inverter (30), and the alternating current side of the inverter (30) is connected to a power grid (70);

the direct current bus of the inverter (30) recommends reference input voltage, the control module (52) can obtain operation information of the optimizer (40) and the inverter (30), the control module (52) recommends reference duty ratio for each series connection body (20) according to the real-time operation information of the optimizer (40) and by referring to the direct current bus reference input voltage, and the optimizer (40) adjusts actual duty ratio in a floating range of the recommended reference duty ratio.

2. The irradiation and temperature adaptive voltage optimization controlled ultra-long string photovoltaic system according to claim 1, further comprising an information acquisition module (51), wherein the information acquisition module (51) can obtain an input voltage of a maximum power point of each optimizer (40) in the string (20), and the average input voltage is obtained by processing the input voltage by the control module (52); the control module (52) obtains the reference output voltage of the optimizer (40) according to the reference input voltage of the direct current bus and the number processing of the optimizers (40), and the control module (52) obtains the recommended duty ratio according to the average input voltage of the optimizers (40) and the reference output voltage processing of the optimizers (40).

3. The irradiation and temperature adaptive voltage optimization controlled extra-long string photovoltaic system according to claim 2, wherein the optimizer (40) is a Buck-type or a Buck-Boost type Buck-Boost DC/DC conversion circuit, and the inverter (30) is a single-stage DC/AC conversion circuit without Boost voltage or a two-stage DC/AC conversion circuit with Boost voltage; the control module (52) obtains the recommended duty cycle based on a division of the average input voltage of the optimizer (40) and a reference output voltage of the optimizer (40).

4. The irradiation and temperature adaptive voltage optimization controlled ultra-long string photovoltaic system according to claim 1, further comprising an information acquisition module (51) and a judgment module (50), wherein the information acquisition module (51) can acquire the input current of each optimizer (40) in the series connection body (20), and the judgment module (50) sets the recommended duty ratio so that the ratio of the actual input current to the recommended duty ratio of the optimizer (40) is smaller than the rated maximum output current of the optimizer (40); the judging module (50) sets a recommendable maximum threshold value of the recommended duty ratio according to the ratio of the input current to the rated output current in the extreme environment.

5. The irradiation and temperature adaptive voltage optimization controlled ultra-long string photovoltaic system according to claim 1, further comprising an information acquisition module (51) and a judgment module (50), wherein the information acquisition module (51) can obtain the actual input voltage of the dc bus of the inverter (30), the judgment module (50) compares the actual input voltage of the dc bus with the currently recommended reference input voltage of the dc bus and makes a judgment, if the difference between the actual input voltage and the currently recommended reference input voltage of the dc bus exceeds a set proportion, the recommended reference input voltage of the dc bus of the inverter (30) is adjusted, and the recommended reference duty ratio of the power optimizer (40) of each series (20) is adjusted accordingly until the difference between the actual input voltage and the currently recommended reference input voltage of the dc bus is within the set proportion.

6. The irradiance and temperature-adaptive voltage-optimized control superlong string photovoltaic system according to claim 5, wherein the switching frequency of the power device operation of the optimizer (40) is higher than the switching frequency of the inverter (30) switching device operation; in the operation period of the inverter (30), if consistency mismatch exists among the series bodies (20), the inverter (30) tracks the maximum power point of the parallel series bodies (20) in a set proportion so as to adjust the direct current bus voltage, and an optimizer (40) in each series body (20) adjusts the actual duty ratio in a floating range of the reference duty ratio along with the adjustment of the actual direct current bus voltage; in the operation period of the optimizer (40), if the non-uniformity mismatch exists in the series body (20), the direct current bus voltage is not changed, and the actual duty ratio is adjusted in a floating range of the reference duty ratio by each optimizer (40) in the series body (20) with the non-uniformity mismatch to maintain the output current to be consistent.

7. The irradiation and temperature adaptive voltage optimization controlled ultra-long string photovoltaic system according to claim 1, further comprising an information acquisition module (51) and a judgment module (50), wherein the information acquisition module (51) acquires a grid-connected point voltage UT at an ac side of the photovoltaic inverter (30), the judgment module (50) compares the grid-connected point voltage UT with a power frequency voltage, judges whether the photovoltaic inverter (30) is in a normal operation mode or a high voltage operation mode, and recommends a corresponding initial reference input voltage for a dc bus input to the inverter (30) according to different operation modes.

8. The irradiation and temperature adaptive voltage optimized control ultra-long string photovoltaic system according to claim 1, wherein the photovoltaic power generation unit is a photovoltaic module, or a series-parallel connection structure of a part of photovoltaic cells in a photovoltaic module; two or more of the series bodies (20) are connected in parallel with each other and output ends thereof are connected to input ends of an inverter (30); the total capacity of the photovoltaic power generation units of each series body (20) is equivalent to the installation relative position; the capacities of the photovoltaic power generation units connected with the optimizers (40) are equivalent; each photovoltaic power generation unit in the series-connected body (20) is installed in the vertical direction, and the photovoltaic power generation units are all connected in series through photovoltaic battery pieces in the transverse direction of installation.

9. A method for irradiation and temperature adaptive voltage optimization control is characterized by being applied to a grid-connected photovoltaic power generation system, wherein the grid-connected photovoltaic power generation system comprises a photovoltaic power generation unit, an optimizer (40) and an inverter (30); the input end of the optimizer (40) is connected to the output end of the photovoltaic power generation unit and tracks the maximum power point of the photovoltaic power generation unit, the output ends of the optimizer (40) are connected in series to form a series body (20), and the output end of the series body (20) is connected to a direct current bus of the inverter (30), and the method comprises the following steps: acquiring operation information of an optimizer (40) and an inverter (30), and recommending a reference input voltage for a direct current bus; recommending reference duty ratios for the series bodies (20) according to real-time operation information of the optimizer (40) and by referring to the reference input voltage of the direct-current bus; the optimizer (40) adjusts the actual duty cycle within a floating range of the recommended reference duty cycle.

10. The irradiation and temperature adaptive voltage optimization control method according to claim 9, wherein the method is applied to a grid-connected photovoltaic power generation system, specifically, the operation frequency of the optimizer (40) is higher than that of an inverter (30), the optimizer (40) is a Buck-type Buck-Boost or a Buck-Boost-type Buck-Boost DC/DC conversion circuit, the inverter (30) is a single-stage DC/AC conversion circuit without Boost voltage or a two-stage DC/AC conversion circuit with Boost voltage, and the method includes the specific steps of:

obtaining a grid-connected point voltage UT at the AC side of the inverter (30), comparing and judging according to the UT and a grid-connected point power frequency reference voltage, and if the UT is less than or equal to 1.1p.u., judging that the inverter (30) is in a normal working mode; if UT is>1.1p.u., then the inverter (30) is judged to be in a high voltage working mode, and the initial U of the direct current bus is set correspondingly according to different working modes_dcref；

When in the normal working mode, setting the initial DC bus reference input voltage U_dcrefAnd each optimizer (40) in the tandem (20) sets a matched reference duty cycle D_refWherein the duty ratio D is referenced_refReference input voltage U from DC bus_dcrefAnd the sum of the input voltages of the optimizers (40) in the series (20) ∑ U_inThe division value of (a); the obtained actual input voltage U_dcAnd a reference input voltage U_dcrefAnd (4) comparing and judging: if the direct current bus is | (U)_dc-U_dcref)/U_dcrefIf | exceeds the set proportion, readjusting U_dcrefAnd is provided with D_refUp to U_dcAnd U_dcrefSatisfy | (U)_dc-U_dcref)/U_dcrefThe ratio is not more than the set ratio; if the direct current bus is | (U)_dc-U_dcref)/U_dcrefIf I does not exceed the set proportion, the current reference input voltage U is used_dcrefAnd a reference duty cycle D_refOperating until the inverter (30) tracks the maximum power point operating cycle changes U_dcOr the inverter (30) is fed back to the DC bus line side to change U_dcAnd make | (U)_dc-U_dcref)/U_dcrefI exceeds a set proportion;

in each operating cycle of the inverter (30), if there is a mismatch in consistency between the series-connected bodies (20), the inverter (30) switches between U and U_dcrefThe actual input voltage U of the direct current bus for tracking the maximum power point in the set proportion_dc(ii) a Following the actual input voltage U_dcOptimizers (40) in each tandem (20) inReference duty cycle D_refThe actual duty ratio D is adjusted within the floating range of (D) to balance the consistency mismatch among the series bodies (20);

during each operational cycle of the optimizer (40), if there is a non-uniformity mismatch within the series (20), the DC bus voltage U_dcInvariably, the output current is maintained consistent by each optimizer (40) in the non-uniformly mismatched serial body (20) according to the reference duty cycle D_refTo adjust the actual duty cycle D within the floating range of (D) to balance non-uniformity mismatches within the series (20);

when in the high voltage operating mode, the bus reference U_dcrefSet outside the maximum power point voltage tracking range of the inverter (30) by adjusting the reference input voltage U_dcrefRespective optimizers (40) in the tandem (20) set matching reference duty cycles D_refUntil the direct current bus (U)_dc-U_dcref)/U_dcrefL does not exceed a set proportion;

the input current of the optimizer (40) is obtained, the recommended duty ratio is set to meet the requirement, and the ratio of the real-time input current of the optimizer (40) to the recommended duty ratio is smaller than the rated maximum output current of the optimizer (40).