CN114142525A - Dual-mode optimal control photovoltaic power generation system - Google Patents

Dual-mode optimal control photovoltaic power generation system Download PDF

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Publication number
CN114142525A
CN114142525A CN202111550141.7A CN202111550141A CN114142525A CN 114142525 A CN114142525 A CN 114142525A CN 202111550141 A CN202111550141 A CN 202111550141A CN 114142525 A CN114142525 A CN 114142525A
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conversion stage
control module
voltage
stage
conversion
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宋悦
陈泽熙
陈楠希
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Shenzhen Zhongxu New Energy Co ltd
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Shenzhen Zhongxu New Energy Co ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
    • H02J13/00006—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment
    • H02J13/00022—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment using wireless data transmission
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/70—Smart grids as climate change mitigation technology in the energy generation sector
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S10/00—Systems supporting electrical power generation, transmission or distribution
    • Y04S10/12—Monitoring or controlling equipment for energy generation units, e.g. distributed energy generation [DER] or load-side generation
    • Y04S10/123—Monitoring or controlling equipment for energy generation units, e.g. distributed energy generation [DER] or load-side generation the energy generation units being or involving renewable energy sources
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S40/00—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them
    • Y04S40/12—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them characterised by data transport means between the monitoring, controlling or managing units and monitored, controlled or operated electrical equipment
    • Y04S40/126—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them characterised by data transport means between the monitoring, controlling or managing units and monitored, controlled or operated electrical equipment using wireless data transmission

Abstract

The invention relates to a dual-mode optimal control photovoltaic power generation system, and relates to the technical field of photovoltaic grid-connected power generation. The photovoltaic power generation system can operate in two different modes according to conditions, and in the first operation mode of variable bus voltage, the system can utilize the input voltage regulation function of the second conversion stage to enable real-time data of duty ratios of the first conversion stages to meet optimization requirements, so that the duty ratios operate in a high-efficiency interval, and the energy decoupling problem of a two-stage conversion structure is solved; under the second operation mode of the fixed bus voltage, the input voltage of the second conversion stage is set at the threshold value for guaranteeing the safety of the second conversion stage, and the first operation mode is actively switched until the duty ratio data meets the tracking condition again under the influence of environmental factors, so that the photovoltaic power generation system can efficiently operate under the normal environment, and meanwhile, the system safety can be guaranteed under the extreme environment.

Description

Dual-mode optimal control photovoltaic power generation system
Technical Field
The invention relates to the technical field of photovoltaic power generation, in particular to a dual-mode optimal control photovoltaic power generation system.
Background
Existing photovoltaic power generation systems are equipped with photovoltaic power optimizers at the photovoltaic module level. The photovoltaic Power optimizer acquires direct current Power of a photovoltaic assembly, and the Maximum Power Point Tracking (MPPT) (maximum Power Point tracking) function of a fast assembly level is realized after Power conversion processing. The photovoltaic power optimizer may be a BUCK, BOOST or BUCK-BOOST conversion topology. Generally, a plurality of optimizers subjected to direct current power conversion are connected to a photovoltaic inverter through a direct current bus side after being serially connected and boosted, and are converted into alternating current capable of being connected to a power grid in the inverter again.
Because the optimizer controls the energy of the photovoltaic component, and the inverter controls the energy of the serially connected optimizer, the control between the two conversion stages has an energy relationship. Therefore, it is necessary to realize energy decoupling of the two conversion stages by adjusting the voltage on the dc bus side, so that the energy of any one input mainly controls the energy of the corresponding one output, and the influence on the energy of the other output is as small as possible. The current direct current bus voltage control strategy of the inverter can be divided into a fixed direct current bus voltage and a variable direct current bus voltage.
The control strategy scheme of the fixed direct current bus voltage is to set the direct current bus voltage of the inverter at a fixed value and not perform MPPT work any more, and each power optimizer performs MPPT work. When the voltage of the direct current bus is kept fixed, the strategy needs to continuously communicate to obtain the power information of each photovoltaic module, calculate and set the output voltage distributed to each power optimizer so as to coordinate the energy relationship of two conversion levels. The problem of the strategy is that the requirement on acquisition and control precision is high, and meanwhile, the optimizer must adopt a BUCK-BOOST type structure with higher cost.
The control strategy scheme of the variable direct-current bus voltage is that a centralized inverter is adopted, the inverter still keeps the MPPT function, and simultaneously each power optimizer with a BUCK type structure carries out MPPT operation. The dc bus voltage regulation of this strategy will track the maximum power point of the multi-string optimizer series line. When part of the photovoltaic modules are shielded, the voltage change of the maximum power point of the direct current bus is not large, the optimizers corresponding to the shielding modules output voltage reduction and current rise by means of communication, and the optimizers operate in a duty ratio range with a low value, so that the working efficiency of the system is influenced.
Accordingly, a better energy decoupling strategy may be provided in a photovoltaic power generation system incorporating a photovoltaic power optimizer by integrating the advantages of both variable and fixed strategies and improving upon solving the problems of the prior art described above.
Disclosure of Invention
In view of this, the present invention provides a dual-mode optimal control photovoltaic power generation system in a main aspect, and a dual-mode control scheme of switching between a variable voltage and a fixed bus voltage according to a situation is adopted, so that a problem that a duty ratio operates in a low-efficiency region due to two-stage MPPT in an existing bus voltage variable control strategy can be solved, and meanwhile, safety is guaranteed in an extreme environment by combining with the bus voltage fixed control strategy, and finally, both high efficiency and safety of the photovoltaic power generation system are achieved.
Based on the same inventive concept as the photovoltaic power generation system, the invention also correspondingly provides a control method and a photovoltaic inverter applied to the photovoltaic power generation system in a secondary aspect, and the bus voltage can be set in two modes to perform power conversion stably and efficiently.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a dual-mode optimally controlled photovoltaic power generation system comprising a second conversion stage and a plurality of first conversion stages; the input end of each first conversion stage is respectively connected with a photovoltaic cell unit, the output ends of a plurality of first conversion stages are mutually connected to form a series circuit, each first conversion stage is respectively provided with a first control module, each first control module is respectively used for tracking the maximum power point input voltage of the corresponding first conversion stage and adaptively setting the duty ratio of the first conversion stage according to the output voltage of the corresponding first conversion stage; the input end of the second conversion stage is connected with the output end of the series circuit, the second conversion stage is provided with a second control module, when the input voltage of the second conversion stage does not exceed the preset voltage range, the second control module sets the input voltage of the second conversion stage in a first operation mode, and when the input voltage of the second conversion stage exceeds the preset voltage range, the second control module sets the input voltage of the second conversion stage in a second operation mode; the second control module of the first operating mode is used for variably adjusting the second conversion stage input voltage to enable the first conversion stage duty ratio data to meet the preset optimization requirement, and switching to the second operating mode until the second conversion stage input voltage exceeds the preset voltage range; the second control module of the second operating mode is configured to set the second converter stage input voltage at a threshold of a preset voltage range, and the second control module of the second operating mode is further configured to adjust the second converter stage input voltage to within the preset voltage range to switch to the first operating mode when the first converter stage duty cycle data satisfies a preset tracking condition.
Optionally, in the photovoltaic power generation system, the second control module is configured to obtain duty ratio data of the first conversion stage and process the duty ratio data into a duty ratio reference amount, and the second control module is provided with an optimization reference range in advance for the duty ratio reference amount; the second control module of the first operating mode being configured to variably adjust the second converter stage input voltage to cause the first converter stage duty cycle data to meet predetermined optimization requirements comprises: the second control module of the first operating mode is configured to variably adjust the second converter stage input voltage such that the duty cycle reference of the first converter stage does not exceed the optimal reference range.
Optionally, in the photovoltaic power generation system, the second control module is configured to obtain duty ratio data of the first conversion stage and process the duty ratio data into a duty ratio reference amount, and the duty ratio reference amount includes: the second control module is used for sequencing and sampling the acquired duty ratio data of the first control module so as to process a duty ratio sampling set with a preset proportion and a front rank as a duty ratio reference; and/or the second control module is used for carrying out mean value processing on the acquired duty ratio data of the first control module so as to process the mean value of the duty ratio data as a duty ratio reference.
Optionally, the second control module of the first operating mode is configured to variably adjust the second converter stage input voltage to enable the duty cycle reference of the first converter stage not to exceed the optimized reference range, and the second control module of the first operating mode comprises: when the duty ratio reference quantity exceeds the optimization reference range, the second control module adjusts the input voltage of the second conversion stage by correspondingly increasing the first amplitude value or reducing the first amplitude value; when the duty ratio reference quantity does not exceed the optimization reference range, the second control module maintains the input voltage of the second conversion stage unchanged.
Optionally, the second control module is provided with a tracking reference range in advance for the reference amount of the duty ratio; the second control module of the second operating mode is further configured to adjust the second converter stage input voltage to within the preset voltage range when the first converter stage duty cycle data satisfies the preset tracking condition, including: the second control module of the second operating mode is further configured to adjust the second control module to within the predetermined voltage range by adjusting the second converter stage input voltage when the duty cycle reference of the first converter stage does not exceed the tracking reference range.
Optionally, in the photovoltaic power generation system, when the duty ratio reference of the first conversion stage does not exceed the tracking reference range, the second control module in the second operation mode is further configured to adjust the input voltage of the second conversion stage to be within a preset voltage range, including: when the duty ratio reference quantity exceeds the tracking reference range, the second control module is used for setting the input voltage of the second conversion stage at the threshold value of the preset voltage range; when the duty ratio reference quantity does not exceed the tracking reference range, the second control module is used for increasing or decreasing the second amplitude value by taking the duty ratio reference quantity adjusted to be within the preset voltage range as a destination to adjust the input voltage of the second conversion stage.
Optionally, the photovoltaic power generation system further includes a second control module, wherein the second control module is provided with an optimization reference range including a first lower limit duty value and a first upper limit duty value, and the second control module is provided with a tracking reference range including a second lower limit duty value and a second upper limit duty value, wherein the second lower limit duty value is smaller than the first lower limit duty value, and the second upper limit duty value is larger than the first upper limit duty value.
Optionally, in the photovoltaic power generation system, the second control module is provided with a preset voltage range including a lower limit voltage threshold and an upper limit voltage threshold; the second control module of the second operating mode is configured to set the second converter stage input voltage at the threshold of the preset voltage range, including when the input-side real-time voltage of the second converter stage is greater than or equal to the upper-limit voltage threshold, the second control module fixedly sets the second converter stage input voltage at the upper-limit voltage threshold; when the input side real-time voltage of the second conversion stage is less than or equal to the lower limit voltage threshold, the second control module fixedly sets the input voltage of the second conversion stage at the lower limit voltage threshold; the first conversion stage is of a BUCK voltage reduction DC-DC conversion topological structure, the first control module is used for generating a pulse width modulation signal capable of controlling the first conversion stage, and the duty ratio of the pulse width signal is set in a self-adaptive mode according to the tracked maximum power point input voltage of the first conversion stage and the voltage parameter configured at the output end of the first conversion stage by the series circuit; the second conversion stage is a DC-AC inverter circuit, and the second control module is used for performing inversion conversion within a rated regulation range of input voltage in a double closed-loop mode by taking the requirement of a power grid as a destination; the second conversion stage acquires duty ratio data of the first conversion stage in a communication mode; the preset optimization requirement is that the duty ratio data optimization reference range with the intermediate value between 0.8 and 0.95 is arranged, and the interval width of the optimization reference range is between 0.005 and 0.02.
In a second aspect, the present invention provides a control method, applied to the above-mentioned photovoltaic power generation system, the photovoltaic power generation system including a second conversion stage and a plurality of first conversion stages, an input end of each of the first conversion stages being connected to a photovoltaic cell, output ends of the plurality of first conversion stages being connected to each other to form a series circuit, an input end of the second conversion stage being connected to an output end of the series circuit, the control method including: in each first conversion stage, respectively tracking the maximum power point input voltage of the corresponding first conversion stage, and adaptively setting the duty ratio of the first conversion stage according to the output voltage of the corresponding first conversion stage; in each second conversion stage, when the input voltage of the second conversion stage does not exceed the preset voltage range, the input voltage of the second conversion stage is set in a first operation mode, and when the input voltage of the second conversion stage exceeds the preset voltage range, the input voltage of the second conversion stage is set in a second operation mode; in the first operating mode, the second converter stage input voltage is variably set in order to satisfy a predetermined optimization requirement for the first converter stage duty cycle data, and is switched to the second operating mode until the second converter stage input voltage exceeds a predetermined voltage range; and under the second operation mode, setting the input voltage of the second conversion stage at the threshold value of the preset voltage range, and adjusting the input voltage of the second conversion stage to be within the preset voltage range until the duty ratio data of the first conversion stage meets the preset tracking condition so as to switch to the first operation mode.
In a third aspect, the present invention provides a photovoltaic inverter apparatus comprising a second inverter stage having a DC-AC conversion topology and a DC bus side for connecting to a series line formed by a plurality of first inverter stages connected together, a second control module for setting a second inverter stage input voltage in a first operation mode when the second inverter stage input voltage does not exceed a preset voltage range, setting a second inverter stage input voltage in a second operation mode when the second inverter stage input voltage exceeds the preset voltage range, the second control module in the first operation mode for adjusting the DC bus side voltage so that the first inverter stage duty ratio data satisfies a preset optimization requirement, switching to a second operation mode until the voltage of the direct current bus side exceeds a preset voltage range; the second control module in the second operation mode is used for setting the direct current bus side voltage at a threshold value of a preset voltage range; and the second control module in the second operation mode is further used for adjusting the voltage of the direct current bus side to be within a preset voltage range when the duty ratio data of the first conversion stage meets a preset tracking condition so as to switch to the first operation mode.
Compared with the prior art, the invention has the following beneficial effects:
(1) the photovoltaic power generation system can operate in two different modes according to conditions, and in the first operation mode of variable bus voltage, the system can utilize the input voltage regulation function of the second conversion stage to enable real-time data of duty ratios of the first conversion stages to meet optimization requirements, so that the duty ratios can operate in a high-efficiency interval and the energy decoupling problem of a two-stage conversion structure is solved; under the second operation mode of the fixed bus voltage, the input voltage of the second conversion stage is set at the threshold value for guaranteeing the safety of the second conversion stage, and the first operation mode is actively switched until the duty ratio data meets the tracking condition again under the influence of environmental factors, so that the photovoltaic power generation system can efficiently operate under the normal environment, and meanwhile, the system safety can be guaranteed under the extreme environment. The invention comprehensively improves the generating efficiency, the construction cost control, the safety and the stability of the photovoltaic generating system and the intelligent level.
(2) The actual duty ratio of a single first conversion stage is determined according to the locally acquired output voltage parameter condition, the second conversion stage indirectly influences the control mode of the output voltage of the first conversion stage by influencing the total voltage of a series circuit instead of setting the control mode as a uniform parameter, and the MPPT control method has the characteristics of self-adaption, flexibility and stability, can solve the problem of voltage mismatch of series photovoltaic modules and further improves the photovoltaic power generation amount.
(3) The photovoltaic power generation system can collect scattered working information data of the first conversion level in a low-cost wireless communication mode, and system intellectualization is realized on the basis of controllable cost; the photovoltaic power optimizer with the BUCK voltage reduction topological structure and lower cost can be used in the first conversion stage, power conversion work can be well completed under various extreme conditions, input voltage regulation of the inverter can be easily maintained within a rated threshold range, and high-efficiency, low-cost, good-stability and intelligent voltage control is achieved.
The invention will be further described with reference to the accompanying drawings.
Drawings
FIG. 1 is a schematic diagram of a circuit structure of a photovoltaic power generation system according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a circuit and a control structure of a photovoltaic inverter applied to a photovoltaic power generation system according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a circuit and control structure of a component power optimizer applied to a photovoltaic power generation system according to an embodiment of the present invention;
fig. 4 is a schematic flow chart of a control method applied to a photovoltaic power generation system according to an embodiment of the present invention;
FIG. 5 is a flow chart illustrating a control method of the component power optimizer according to an embodiment of the present invention;
fig. 6 is a schematic flow chart illustrating a control method of the photovoltaic inverter according to an embodiment of the present invention;
fig. 7 is a schematic view illustrating a processing flow of duty ratio data in the control method according to the embodiment of the present invention.
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.
Examples
Fig. 1 illustrates a dual-mode optimally controlled photovoltaic power generation system implemented in accordance with a first aspect of the present invention. The photovoltaic power generation system comprises a photovoltaic inverter device according to an embodiment of the third aspect of the invention and a component power optimizer. The photovoltaic inverter apparatus includes a second conversion stage 31 and a second control module 32, and may be simply referred to as an inverter 30. The above-described component power optimizer comprises a first conversion stage 11 and a first control module 12, and may be referred to simply as optimizer 10. The outputs of the plurality of optimizers 10 are connected in series with each other to form a series line 20, the series line 20 being connected to the dc bus side 311 of the inverter 30. Optimizer 10 is capable of taking input power from photovoltaic cells 90 and performing MPPT tracking. The inverter 30 is able to draw input power from the series connection 20 and, in the first operating mode and in the second operating mode, to switch to the input voltage setting of the second converter stage 31, i.e. to set the input voltage on the dc bus side 311 of the inverter 30, i.e. to set the output voltage of the series connection 20. The first mode of operation is a variable dc bus voltage control strategy and the second mode of operation is a fixed dc bus voltage control strategy. In the first mode of operation the second converter stage 31 inputs a voltage variation setting and enables the duty cycle data to meet the preset optimization requirements, and in the second mode of operation the second converter stage 31 inputs a voltage fixation setting and monitors the timing at which the duty cycle data meets the preset tracking conditions.
In the optimizer 10, the first conversion stage 11 is a dc-dc conversion circuit, and includes a switching device for turning on, turning off, and bypassing the input power to perform power conversion, and energy storage devices such as an inductor and a capacitor for filtering the converted power, in order to perform power conversion on the input power with the maximum power point tracking as a destination. The first control module 12 can generate a PWM signal (Pulse Width Modulation) to control a switching device in the dc-dc conversion circuit. The first control module 12 drives the power conversion of the first conversion stage 11 by setting the duty ratio D of the PWM signal, and makes the operation parameters of the first conversion stage 11 satisfy the quantitative relationship. For example, in the first conversion stage 11, which is a BUCK DC-DC conversion topology, the operating parameters satisfy the relationship: input voltage UpvMultiplied by the duty cycle D to be equal to the output voltage Uout. Meanwhile, the first control module 12 may adjust the duty ratio D by the maximum power tracking algorithm to make UpvMaximum power point voltage U approaching photovoltaic modulempp。
In the series line 20, the optimizer 10 is provided with n (n.gtoreq.2) in particular. In the optimizers 10, which are designated 1 to n, a photovoltaic cell 90 is connected to the input of each first conversion stage 11. The photovoltaic cell 90 may be one or more encapsulated photovoltaic modules, or a string of partial cells within the encapsulation of a photovoltaic module. The outputs of the n first conversion stages 11Are connected in series with each other to form a series line 20. The series line 20 is also referred to as a photovoltaic string. The output terminal of the series line 20 is connected to the dc input side of the inverter 30. The n first conversion stages 11 are provided with n first control modules 12 in one-to-one correspondence. The n first control modules 12 can obtain the input voltages { U ] of the n corresponding first conversion stages 11 in a one-to-one correspondence mannerpv1、Upv2、…、UpvnIs able to obtain an input current I of its corresponding first conversion stage 11pv1、Ipv2、…、IpvnAnd tracking the maximum power point MPP of the corresponding photovoltaic cell unit 90. The n first control modules 12 can also obtain the output voltages { U ] of the corresponding first conversion stages 11out1、Uout2、…、UoutnN first conversion stages 11 have n independent duty cycle data, i.e. { D }1、D2、…、Dn}. When the first conversion stage is of BUCK structure, the duty ratio D is for any of the xth first control modules 12 in the range of 1 to nx=Uoutx/Upvx. In the present embodiment, one series line 20 is schematically provided, and in other embodiments, the series lines 20 may be provided in m strings (m ≧ 2) in parallel with each other. The duty cycle data is denoted D, D comprising the duty cycles of all first conversion stages 11 of a series connection 20, i.e., D =d1、D2、…、Dn}. In other examples, the duty cycle data may also include the duty cycles of m × n first conversion stages 11.
In the inverter 30, the second conversion stage 31 is a dc-ac inverter circuit in the present embodiment, and may also be a dc-dc conversion preceding stage of the inverter 30 in other embodiments, for example, a BOOST conversion preceding stage. In this embodiment, the second conversion stage 31 can obtain dc power from the dc bus 311, convert the dc power into ac power by inverter conversion, and output the ac power to the grid-connected ac side 312. That is, the second conversion stage 31 performs the inverter conversion of the output dc power of the series circuit 20. The second control module 32 controls the inversion process in order to meet the grid requirements and is able to regulate the dc bus side 311 within the rated regulation range of the input voltage. In particular, the direct current bus of the second conversion stage 31 to be detected in real timeVoltage UbusAdjusting to DC bus reference voltage Uref。
Wherein the second control module 32 is capable of obtaining U of the second conversion stage 31 by real-time acquisitionbus(and also the output voltage of the series line 20) is compared to a predetermined voltage range and the operating mode of the second control module 32 is determined. The preset voltage range includes a lower voltage threshold UrefLAnd an upper voltage threshold UrefHRecord as (U)refL，UrefH). When U is turnedbusIn (U)refL，UrefH) Range, the second control module 32 operates in the first mode of operation when UbusExceed (U)refL，UrefH) In the second mode, the second control module 32 operates in the second mode of operation.
In the first operation mode, the second control module 32 can variably adjust the input voltage of the second conversion stage 31, i.e. adjust the dc bus reference voltage of the inverter, so that the duty ratio data { D } of each first conversion stage 11 in each series circuit 20 can satisfy the preset duty ratio optimization requirement { D }max. When the duty cycle optimization requirement is met, the first conversion stage 11 can reduce the current ripple through the energy storage component, and then the optimizer 10 reduces the loss, prolongs the service life, and reduces the cost. { D }maxMay be a preset value or a preset range related to the duty cycle of the first conversion stage 11, or may be a plurality of preset values or preset ranges switchable according to a setting condition. Second control module 32 is capable of raising/lowering variably adjustable UrefThe adjustment amplitude is a predetermined first amplitude, such as 0.2V. In turn, the series line 20 output voltage will vary accordingly, which in turn causes the series line 20 to be distributed to U of each first conversion stage 11outVaries in its entirety. Satisfy U in BUCK topologyout=UpvD. At a certain moment when environmental factors do not influencepvSet to U by MPPT operationmppDue to UoutThe up/down adjustment is made and D will also make the up/down adaptive adjustment accordingly. The second control module 32 in the first mode of operation may obtain duty cycle data { D } for each first conversion stage 11, together with duty cycle optimization requirements{D}maxAnd (3) comparing and judging: when { D } satisfies { D }maxThen the second control module 32 sets U unchangedrefWhen { D } does not satisfy { D }maxThe second control module 32 may variably adjust U up/downref. Eventually the actual operating duty cycle D of the first conversion stage 11 can be stabilized at or near the duty cycle optimization requirement.
In the second operating mode, the second control module 32 can permanently set the input voltage of the second converter stage 31. When the DC bus reference voltage U is adjusted to meet the requirement of duty ratio optimizationrefAnd make the DC bus voltage UbusOut of a predetermined voltage range (U)refL，UrefH) The second control module 32 switches to the second mode of operation. Specifically, in the second operation mode, if the dc bus voltage U is lower than the first operation modebusGreater than UrefHThe second control module 32 will UrefSet as the upper threshold U of the voltage rangerefHIf the DC bus voltage UbusLess than UrefLThe second control module 32 will UrefSet as the lower threshold U of the voltage rangerefL. At the same time, U is fixedly arrangedrefWill cause the duty cycle data D to no longer satisfy the optimization requirement DmaxIn the second operation mode, the second control module 32 may obtain duty ratio data { D } of each first conversion stage 11 and duty ratio tracking condition { D }minAnd (3) comparing and judging: when { D } does not satisfy { D }minThen the second control module 32 continues to maintain the second operation mode when { D } satisfies { D }minThen the second control module 32 adjusts UrefMake it return to the preset voltage range (U)refL，UrefH) The adjustment amplitude is a predetermined second amplitude value, such as 5V, to switch to the first operation mode.
Briefly, the operation examples of this embodiment are: in the first mode of operation, when U is caused by environmental factors such as radiation and temperaturemppRise, UoutThrough UrefChanging settings to implement following UmppRising and rising, real-time { D } satisfies { D }maxUp to UbusTo reach UrefHAnd switches to the second mode of operation. In the second mode of operation, when environmental factors cause UmppContinuously rise, UoutDue to UrefIs fixedly arranged as UrefHAnd relatively stable according to D = U in BUCK topologyout/UpvReal-time { D } will be less than { D }max(ii) a At this time, { D } continues to be acquired, for example, U is caused by environmental factor changemppThe fallback occurs such that { D } satisfies { D }minThen U isrefSlave UrefHThe reduction is adjusted to 5V to enable UrefSatisfaction of the Range (U)refL，UrefH) And switches to the first operating mode.
It is understood that the preset voltage range (U) is in the present embodimentrefL，UrefH) Is the rated regulating range of the input voltage of the direct current bus; in other embodiments, it may also be not exceeded (U)refL，UrefH) Another range (U) ofref1，Uref2). It will be appreciated that the preset first and second magnitudes are related to the number and parameters of optimizers 10 and the input voltage regulation parameters of inverter 30. Wherein the preset second amplitude is further associated with a duty cycle tracking condition { D }min. The second amplitude is greater than the first amplitude.
It will be appreciated that the input power and output power of the optimizer 10 may be considered constant during dc-dc conversion when the operational consumption of the first conversion stage 11 and the first control module 12 is ignored. Thus, the operating parameters of the optimizer 10 satisfy Upv*D=UoutAlso satisfy Ipv/D=Iout. In other equivalent embodiments, the first control module 12 may be based on the output current IoutWith maximum power point current ImppTo set the duty cycle D; the second control module 32 is used to variably set the output-side current variable I of the second conversion stage 31busMake duty ratio data { D1、D2、…、DnSatisfy the duty ratio optimization requirement { D }max. In general, since the accuracy of detecting the voltage is high, it is preferable as a target of the adjustment.
With respect to duty cycle optimization requirements, it can be appreciated thatAccording to the setting conditions of the optimizer 10 and the inverter 30, a duty ratio optimization requirement { D }can be setmaxThe MPPT requirement of the photovoltaic cell unit 90 on the front side can be met, the input voltage of the inverter 30 on the rear side can be in a safe range, the duty ratio can be operated in a higher range capable of reducing loss, and the efficiency of the system is improved. When the first conversion stage 11 is a BUCK DC-DC conversion topology, operating the duty cycle around 0.9 may reduce the inductor ripple current in the topology. Thus, the duty cycle optimization requirement can be set to optimize the reference range [ D ] according to the degree of current ripple that the inductor in the optimizer 10 can withstand1L，D1H]. In this example [ D1L，D1H]May be set at a value between 0.8 and 0.95, [ D ]1L，D1H]May be set at a value between 0.005 and 0.02. For example, when the median is 0.905 and the span width is 0.01, the optimum reference range is [0.9, 0.91 ]]。
With respect to the duty cycle tracking condition, it will be appreciated that the duty cycle data { D } is optimized by adjusting the DC bus reference voltage UrefThis is an adaptive process and not a direct setting of the control parameters for a single optimizer 10. Meanwhile, the environmental factors have a more unidirectional behavior, so that when the duty ratio data falls back to approach the duty ratio optimization requirement again from exceeding the preset duty ratio optimization requirement due to the environmental factors, the second control module 32 can be set to the first operation mode again. Therefore, the duty ratio tracking condition { D }minIs a tracking reference range, denoted as [ D ]2L，D2H]. Wherein D is2L＜D1L，D2H＞D1H. For example, the reference range setting [0.9, 0.91 ] is optimized]Then the tracking reference range may be set to [0.89, 0.92 ]]。
Regarding the duty ratio data, in the embodiment, specifically, in a series of power buses, the duty ratio data of the first control module 12 is { D }1、D2、…、Dn}. Further processing of the duty cycle data allows for the determination of a fine-tuned parameter target. Duty ratio data { D1、D2、…、DnSorting is carried out, and duty ratio sorting data { D } can be obtained1st、D2nd、…、Dnth}. The duty cycle ordered data is sampled, e.g., at a 20% ratio, to obtain a duty cycle sample set { D }1st、D2nd、…、Dkth}. Wherein k =20% n and k is an integer. The duty ratio data ranked at the top is sampled and selected, and can represent the data that the photovoltaic cell unit 90 is not shielded or the shielding conditions are consistent, and the performance of the photovoltaic cell unit 90 for really receiving and converting photovoltaic power can be reflected. Therefore, the optimum reference range and the tracking reference range can be set with the standard parameters of the photovoltaic cell. Since the duty ratio optimization control parameters are not directly set for a single optimizer 10, when 20% of the optimizers 10 can meet the optimization reference range or the tracking reference range, other photovoltaic cells with non-uniform occlusion are allowed to operate in a close range, and the duty ratio optimization requirement can also be met.
Regarding the duty ratio data, in the embodiment, specifically, the duty ratio data for the duty ratio optimization requirement may be that the duty ratio data of all the first control modules 12 in a series of power buses is { D }1、D2、…、DnAnd performing average processing on the duty ratio data. It is understood that other embodiments may also employ a median processing method, for example, or other processing methods that may simplify the differential and numerous duty cycle data.
Fig. 2 shows a circuit configuration of an embodiment of a photovoltaic inverter apparatus according to a third aspect of the present invention. The inverter 30 includes an inverter circuit as a second conversion stage 31, and an inverter controller as a second control module 32. The inverter circuit is connected with m series circuits 20, and each series circuit 20 is formed by connecting n optimizers 10 in series. The output of the series line 20 is connected to the dc bus side 311 of the inverter circuit, and the ac grid side 312 of the inverter circuit is connected to the grid connection point. The inverter controller is illustratively a dual closed-loop control structure 324 that includes a current inner loop and a voltage outer loop. Wherein: the current inner loop is mainly composed of uGNetwork voltage link iGThe current sampling link and the sin ω t voltage are the sameThe step link, the current regulator and the driving link are formed, so that the inversion from direct current to alternating current and the sine wave current control of the power factor of the network side unit are realized; wherein the voltage outer ring mainly consists of UbusDC bus voltage detection, voltage regulator to make the U change within the rated rangerefThe rated network voltage u can be formed on the ac grid side 312GAnd (6) outputting.
In particular, the inverter controller of the present embodiment further comprises a duty cycle optimization loop. Wherein the duty cycle optimization loop is configured to output U satisfying a duty cycle optimization reference range in the first operation moderef±△1A bus voltage reference command for outputting U in the second operation moderefLOr UrefHAnd for outputting U when the second operating mode is switched to the first operating moderefL+△2Or UrefH-△2The bus voltage reference command. The duty cycle optimization loop includes: a duty ratio data processing unit 321, a duty ratio optimization tracking unit 322, and an upper and lower limit voltage limiting unit 323. The upper and lower limit voltage limiting unit 323 is used for limiting the voltage of UrefExceed (U)refL，UrefH) When it is turned into UrefIs correspondingly set as UrefLOr UrefH. The duty ratio data processing unit 321 is configured to obtain the duty ratio data { D } of each optimizer 10 in the serial connection 20 through the wireless receiving unit 40, and process the duty ratio data { D } into the reference duty ratio DrefThe duty ratio optimization tracking unit 322 is used for referencing the duty ratio by a reference amount D in the first operation moderefAnd an optimized reference range [ D1L，D1H]Comparing to obtain the current bus input voltage UbusOutput dc bus reference voltage UrefInstructions; and for referencing the duty cycle by an amount D in the second mode of operationrefAnd tracking reference range [ D2L，D2H]Comparing to obtain the voltage which is fixed at the upper limit or the lower limit at present to adjust to (U)refL，UrefH) Outputting DC bus reference voltage U within range as destinationrefAnd (5) instructions.
FIG. 3 shows an embodiment of a component power optimizer in accordance with an embodiment of the present inventionThe circuit structure of (1). The optimizer 10 comprises a BUCK conversion circuit as the first conversion stage 11 and a controller as the first control module 12. The BUCK conversion circuit is a circuit structure known in the art, and comprises a conversion input end 111 and a conversion output end 112, and an auxiliary power supply 13 arranged in parallel, an input capacitor C1 arranged in parallel, a switching tube M1 arranged in series, a freewheeling diode D1 arranged in parallel, an inductor L1 arranged in series, an output capacitor C2 arranged in parallel, and a bypass diode D2 arranged in parallel, which are sequentially arranged from the conversion input end 111 to the conversion output end 112. Wherein the conversion input 111 is connected to the photovoltaic cell unit 90 and is provided with an input current IpvAnd input voltage UpvThe sampling member of (1). The transform outputs 112 are connected in series to the outputs of the other optimizers 10 and form a series line 20. Wherein the conversion output 112 is provided with an output current IoutSampling member and output voltage UoutThe sampling member of (1). The sampling elements can sense the change of the electrical parameters of the optimizer 10 and output the change to the controller. The control structure of the controller includes: the MPPT tracking control system comprises an input power sampling link, an MPPT tracking control link, an output voltage feedback link, a voltage regulator, a PWM modulation and driving link. When the photovoltaic power generation system is in operation, the MPP of the photovoltaic cell unit 90 is directly searched by the BUCK conversion circuit through the controller, so that the current U is obtainedpvApproaches to the current UmppAnd according to the output voltage U fed backoutAnd generating a PWM signal for controlling the operation of a switching tube M1 in the BUCK conversion circuit, and adjusting the duty ratio of the PWM signal to realize the maximum power tracking of the photovoltaic cell unit 90. At the same time, the output voltage UoutIs the voltage U of the series line 20 regulated by the inverter controllerbusDistributed to the optimizer 10. Due to the output voltage UoutThrough the duty ratio optimization configuration, the operation duty ratio of the BUCK conversion circuit can meet or approach the optimization reference range [0.9, 0.91 ]]。
In this embodiment, specifically, the number of the optimizers 10 arranged in the series line 20 is large, and the number of the optimizers 20 arranged in the series line is large, so that the duty ratio information of each optimizer 10 is sent to the inverter controller in a network communication manner. In the embodiment, specifically, the optimizers 10 are provided with wireless transmitting units 41, the inverter controller is provided with a wireless receiving unit 40, the controller is provided with a wireless transmitting unit 41, and the duty ratio information of each optimizer 10 is transmitted to the inverter 30 through wireless communication.
Fig. 4 shows a control method according to a third embodiment of the present invention, which is used for the above-mentioned dual-mode optimal control photovoltaic power generation system. The control method comprises the following steps: step S1 and step S2.
Step S1 is a control strategy respectively executed in each first conversion stage 11, and is also a control strategy provided in the optimizer 10. The method specifically comprises the following steps: s1, obtaining the output voltage U of the maximum power point mpp tracked by the first conversion stage 11pvObtaining the output voltage U of the series circuit 20 arranged in the first conversion stage 11outAccording to UpvAnd UoutSets the operating duty cycle D of the first conversion stage 11 and sends duty cycle information D to the second conversion stage.
Step S2 is a control strategy that is run in the second conversion stage 31, and is also a control strategy provided to the inverter 30. Step S2 includes receiving the duty ratio data { D } of each first conversion stage 11, and includes steps S21, S22, and S23. The method specifically comprises the following steps:
s21, obtaining the input voltage U of the second conversion stage 31busAt the second conversion stage 31, the voltage U is inputbusDoes not exceed the preset voltage range (U)refL，UrefH) The input voltage U of the second conversion stage 31 is set in the first operating modebusAt the second conversion stage 31, the voltage U is inputbusExceed (U)refL，UrefH) The input voltage U of the second conversion stage 31 is set in the second operating modebus；
S22, in the first operation mode, in order to make the duty ratio data { D } of the first conversion stage 11 satisfy the preset optimization requirement { D }maxWhile the input voltage U of the second conversion stage 31 is variably adjustablebusUp to the input voltage U of the second conversion stage 31busOut of a predetermined voltage range (U)refL，UrefH) Switching to a second operation mode;
s23, inputting the voltage into the second conversion stage 31 in the second operation modeUbusCorrespondingly setting the threshold value U in the preset voltage rangerefLOr threshold value UrefHUntil the duty cycle data D of the first conversion stage 11 fulfils the preset tracking condition DminBy inputting the voltage U to the second conversion stage 31busAdjusted to a predetermined voltage range (U)refL，UrefH) And is switched to the first operation mode.
FIG. 5 shows a program of the power optimizer of the control module in step S1 according to the control method shown in FIG. 4:
s11, obtaining the input voltage UpvAnd an input current IpvTracking the maximum power point to make UpvTracing to maximum power point voltage Umpp(e.g., perturbation MPP tracking, U responds faster than step S1outApproximately constant, while the adjustment changes UpvIn U atpvJudging whether the current power is at the maximum power point in the change process, thereby ensuring that U is at the maximum power pointpvApproaches to Umpp）；
S12, acquiring the current input voltage UpvObtaining the current output voltage UoutExecuting S13;
s13, according to D = Uout/UpvAdaptively setting the duty ratio D of the current PWM signal, S14 is performed (at this time, Upv=Umpp）；
S14, sending the current duty cycle D to the second control module 32, and returning to the beginning (causing the second control module 32 to regulate the series line 20 output voltage U with the purpose of optimizing the duty cyclebusThus resulting in UoutChange).
It will be appreciated that the duty cycle of the first conversion stage 11 is not regulated to a target value by communication, but rather by the dc bus voltage UbusAfter optimized adjustment of the overall duty cycle data, the output voltage U is configured in the first conversion stage 11outThe duty cycle D can be made numerically to meet or approach the optimization requirements.
Fig. 6 shows a program for specifically controlling the photovoltaic inverter apparatus in step S2 according to the control method shown in fig. 4:
wherein, step S21 specifically includes:
s211, obtaining the current DC bus voltage UbusJudgment of UbusWhether or not in the voltage threshold range (U)refL,UrefH) Otherwise, the step S22 is executed if the result is yes, and the step S23 is executed if the result is no.
Wherein, step S22 specifically includes:
s221, obtaining current duty ratio data { D } of each first conversion stage 11, processing and obtaining a duty ratio reference quantity DrefStep S222 is executed;
s222, comparing and judging the duty ratio reference quantity DrefWhether it is in the optimum reference range [0.9, 0.91 ]]If yes, executing S291; if the result is NO and DrefIf less than 0.9, executing S292; if the result is NO and DrefIf > 0.91, executing S293;
s291, reference voltage U of DC busrefIs maintained at UbusReturning to step S211;
s292, converting the DC bus reference voltage UrefAdjusted to Ubus+0.2V, return to step S211;
s293, converting the DC bus reference voltage UrefAdjusted to Ubus0.2V, return to step S211.
It will be appreciated that the second conversion stage is executing a control strategy for the variable bus voltage in step S22. U in control strategybusCan finally realize the current duty ratio reference quantity DrefTake on the value of [0.9, 0.91 ]]Within the range of (1).
Wherein, step S23 specifically includes:
s231, judging to be Ubus≤UrefLIf yes, go to step S232 to determine if it is Ubus≥UrefHIf so, go to step S233;
s232, converting the DC bus reference voltage UrefIs set and maintained at UrefLSimultaneously executing step S2321;
s2321, obtaining current duty ratio data { D } of each first conversion stage 11, and processing to obtain a duty ratio reference quantity DrefStep S2322 is executed; s2322, duty ratio parameter is compared and judgedConsideration DrefWhether it is in the tracking reference range [0.89, 0.92 ]]I.e. whether D is presentrefLess than or equal to 0.92; if not, returning to the step S232, and if so, executing the step S2323;
s2323, converting the DC bus reference voltage UrefIs set as UrefL+5V, return to S211;
s233, converting the DC bus reference voltage UrefIs set and maintained at UrefHSimultaneously executing step S2331;
s2331, obtaining current duty ratio data { D } of each first conversion stage 11, processing to obtain a duty ratio reference DrefStep S2332 is performed; s2332, comparing and judging the duty ratio reference quantity DrefWhether it is in the tracking reference range [0.89, 0.92 ]]I.e. whether D is presentrefNot less than 0.89, if the result is not, returning to the step S233, and if the result is yes, executing the step S2332;
s2332, reference voltage U of the direct current busrefIs set as UrefH5V, and returns to S211.
It will be appreciated that the second conversion stage is executing a control strategy for fixing the bus voltage in step S23. U in control strategybusRemains fixed, so the duty ratio reference D is maintained under the environment changerefWill exceed the value of [0.89, 0.92 ]]Varying over a range. Meanwhile, step S23 continues to monitor the duty reference DrefWhen D is presentrefSatisfy [0.89, 0.92 ]]In range, by actively bringing UbusIs adjusted to (U)refL,UrefH) And switching the second conversion stage from the control strategy of the fixed bus voltage to the control strategy of the variable bus voltage in a mode within the range.
It is understood that steps S291, S292, S293, S232, and S233 are steps of setting the dc bus voltage. In the BUCK conversion circuit, UoutAnd D is in positive correlation with the sum of D, so that the voltage setting change direction of the direct current bus and the duty ratio reference quantity DrefThe direction of change is regulated to show positive correlation. Steps S2312 and S2322 are also steps for setting the dc bus voltage, so that the dc bus voltage can meet the requirement of the preset voltage range. In other embodiments, the first transformationThe stage 11 may also be a BOOST DC-DC conversion topology, or may also be a BUCK-BOOST DC-DC conversion topology, where the direct current bus voltage setting change direction and the duty ratio reference DrefThe correlation presented by adjusting the direction of change will change accordingly.
Steps S221, S2321 and S2331 are DrefThe acquisition program is a program capable of processing a plurality of duty ratio data into a duty ratio reference amount. FIG. 7 shows the implementation of D in the control method according to FIG. 4refThe specific steps for obtaining the program are as follows:
s241, obtaining current duty ratio data { D ] from each first control module through communication1、D2、…、DnExecuting step S242;
s242, sorting the duty ratio data to obtain sorting data { D1st、D2nd、…、DnthExecution of step S243;
s243, selecting a duty ratio sampling set { D ] with a preset proportion from the sequencing data1st、D2nd、…、DkthWhere k is an ordinal number of a preset ratio and k is an integer (e.g., the preset ratio is 20%, k is an integer of 20% × n), go to step S244;
s244, carrying out mean value processing on the duty cycle sampling set to obtain a duty cycle reference quantity DrefAnd returning to the beginning.
Application examples of the embodiments
Take a certain distributed photovoltaic power generation system installed in east china as an example. The photovoltaic power generation system comprises photovoltaic modules of 72 monocrystalline silicon photovoltaic cells, and each photovoltaic module is provided with the module power optimizer. The photovoltaic power generation system further includes the inverter 30 described above. The 24 photovoltaic modules are respectively provided with the optimizer 10, and are connected in series with each other through the output end of the optimizer 10 to form a photovoltaic module string. The output of the photovoltaic string is connected to the dc bus side 311 of the inverter 30 to form a photovoltaic power generation system.
The parameters of the inverter 30 are: 1100V of maximum direct current input voltage, 380V of rated alternating current output voltage, 610V of bus reference voltage with highest efficiency and voltage threshold value of bus voltage of inverter 30The range is: upper threshold value UrefH=1000V, lower threshold UrefL= 6V. The regulated amplitude of the bus voltage is 0.2V. The duty ratio optimization reference range of the optimizer 10 is set at [0.9, 0.91 ]]。
In the eastern China summer extreme high temperature condition, such as the environment temperature of 42 ℃, the solar radiation of 1100kw/m2, the heat dissipation condition of the photovoltaic module is poor. Tracking of the photovoltaic module by optimizer 10 when the module temperature reaches 75 degrees causes Upv=Umpp= 37V; at this time, the inverter 30 sets the dc bus voltage at U to satisfy the requirement of the duty ratio in the optimized reference rangebus= 728V; the output voltage of the photovoltaic module from the string of photovoltaic strings is approximately 33.3V and the duty cycle is set at 0.9. Tracking of the photovoltaic module by optimizer 10 when the module temperature reaches 85 degrees so that U ispv=Umpp= 32.1V; at this time, in order to meet the requirement that the duty ratio is in the optimized reference range, the inverter 30 sets the dc bus voltage at 693V; the output voltage of the photovoltaic module from the string of photovoltaic strings is approximately 28.9V and the duty cycle is set at 0.9. Whether or not it is Ubus=728V, or UbusAnd =693V, all within the voltage threshold range of the bus voltage.
Therefore, the inverter 30 operating in the first operation mode adjusts the dc bus voltage by acquiring the duty ratio data, so that the duty ratio of the optimizer 10 adaptively operates within the optimized reference range, thereby improving the power generation efficiency of the photovoltaic power generation system.
Under the condition of extremely low temperature in winter in east China, such as the ambient temperature of-10 ℃, and when the sun irradiates 1000kw/m2, the heat dissipation condition of the photovoltaic module is better. Tracking of the photovoltaic module by optimizer 10 when the module temperature reaches-10 degrees enables Upv=Umpp= 47V. If the duty cycle is to meet 0.9, the photovoltaic module goes to 1018U. At this point, inverter 30 is operating in the second operating mode, and inverter 30 no longer tracks the duty cycle optimization requirement, but sets the dc bus voltage to the upper threshold of 1000V. The output voltage of the photovoltaic module distributed from the photovoltaic string is about 41.7V, and the duty ratio is set to 0.88, which is not satisfactory for operation within the optimized reference range. But can ensure the operation safety of the photovoltaic power generation system. At this time, the reverseThe changer 30 tracks the condition { D }by acquiring the duty ratio data and tracking the duty ratio at the duty ratiominAnd (6) comparing. If the temperature changes with the environmental temperature, such as when the sun irradiates 800kw/m2, and the U is enabledpv=Umpp=46.8V, so that the duty ratio data satisfies the duty ratio tracking condition of 0.89, the dc bus voltage is set to 995V. At this point, inverter 30 is operating in the first operating mode, and inverter 30 variably sets the dc bus voltage to follow the duty cycle optimization requirement again.
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 (10)

1. A dual-mode optimally controlled photovoltaic power generation system comprising a second conversion stage (31) and a plurality of first conversion stages (11); the input end of each first conversion stage (11) is respectively connected with a photovoltaic cell (90), the output ends of a plurality of first conversion stages (11) are connected with each other to form a series circuit (20), each first conversion stage (11) is respectively provided with a first control module (12), and each first control module (12) is respectively used for tracking the maximum power point input voltage of the corresponding first conversion stage (11) and adaptively setting the duty ratio of the first conversion stage (11) according to the output voltage of the corresponding first conversion stage (11);
the input end of the second conversion stage (31) is connected to the output end of the series circuit (20), the second conversion stage (31) is provided with a second control module (32), when the input voltage of the second conversion stage (31) does not exceed the preset voltage range, the second control module (32) sets the input voltage of the second conversion stage (31) in a first operation mode, and when the input voltage of the second conversion stage (31) exceeds the preset voltage range, the second control module (32) sets the input voltage of the second conversion stage (31) in a second operation mode;
the second control module (32) of the first operating mode is used for variably adjusting the input voltage of the second conversion stage (31) so that the duty ratio data of the first conversion stage (11) meets the preset optimization requirement, and switching to the second operating mode until the input voltage of the second conversion stage (31) exceeds the preset voltage range;
the second control module (32) of the second operation mode is configured to set the second converter stage (31) input voltage at a threshold of a preset voltage range, the second control module (32) of the second operation mode being further configured to adjust the second converter stage (31) input voltage to within the preset voltage range to switch to the first operation mode when the first converter stage (11) duty cycle data satisfies a preset tracking condition.
2. A dual-mode optimally controlled photovoltaic power generation system according to claim 1, characterized in that the second control module (32) is used for acquiring the duty ratio data of the first conversion stage (11) and processing the duty ratio data into a duty ratio reference, and the second control module (32) is provided with an optimized reference range for the duty ratio reference in advance; the second control module (32) of the first operating mode being configured to variably adjust the input voltage of the second conversion stage (31) such that the duty cycle data of the first conversion stage (11) meets a predetermined optimization requirement comprises:
the second control module (32) of the first operating mode is used for variably adjusting the input voltage of the second conversion stage (31) in order to keep the duty cycle reference of the first conversion stage (11) from exceeding an optimized reference range.
3. A dual mode optimally controlled photovoltaic power generation system according to claim 2 wherein the second control module (32) is adapted to acquire duty cycle data of the first converter stage (11) and to process the duty cycle data as a duty cycle reference comprising:
the second control module (32) is used for sequencing and sampling the acquired duty ratio data of the first control module (12) so as to process a duty ratio sampling set with a preset proportion and a front rank as a duty ratio reference; and/or the presence of a gas in the gas,
the second control module (32) is used for carrying out average value processing on the acquired duty ratio data of the first control module (12) so as to process the average value of the duty ratio data as a duty ratio reference.
4. A dual mode optimally controlled photovoltaic power generation system according to claim 2 wherein the second control module (32) in the first mode of operation is adapted to variably adjust the second converter stage (31) input voltage so that the duty cycle reference of the first converter stage (11) does not exceed the optimal reference range comprising:
when the duty ratio reference exceeds the optimum reference range, the second control module (32) adjusts the input voltage of the second conversion stage (31) by increasing the first amplitude or decreasing the first amplitude accordingly;
when the duty ratio reference quantity does not exceed the optimization reference range, the second control module (32) maintains the input voltage of the second conversion stage (31) unchanged.
5. A dual-mode optimized controlled photovoltaic power generation system according to claim 2, characterized in that the second control module (32) is provided with a tracking reference range in advance for a duty reference; the second control module (32) of the second operating mode is further configured to adjust the input voltage of the second converter stage (31) to within a preset voltage range when the duty cycle data of the first converter stage (11) satisfies a preset tracking condition, including:
the second control module (32) of the second operation mode is further configured to adjust the second control module (32) to within the predetermined voltage range by adjusting the input voltage of the second conversion stage (31) when the duty cycle reference of the first conversion stage (11) does not exceed the tracking reference range.
6. A dual-mode optimally controlled photovoltaic power generation system according to claim 5, wherein said second control module (32) in said second operating mode is further adapted to adjust the second control module (32) by adjusting the second converter stage (31) input voltage to within a preset voltage range when the duty cycle reference of the first converter stage (11) does not exceed the tracking reference range comprises:
when the duty ratio reference quantity exceeds the tracking reference range, the second control module (32) is used for setting the input voltage of the second conversion stage (31) at the threshold value of the preset voltage range;
when the duty ratio reference quantity does not exceed the tracking reference range, the second control module (32) is used for increasing or decreasing the input voltage of the second conversion stage (31) by a second amplitude value by taking the duty ratio reference quantity adjusted to be within the preset voltage range as a destination.
7. A dual mode optimal controlled photovoltaic power generation system according to claim 5, characterized in that the second control module (32) is provided with an optimal reference range comprising a first lower limit duty cycle value and a first upper limit duty cycle value, the second control module (32) is provided with a tracking reference range comprising a second lower limit duty cycle value and a second upper limit duty cycle value, wherein the second lower limit duty cycle value is smaller than the first lower limit duty cycle value, and the second upper limit duty cycle value is larger than the first upper limit duty cycle value.
8. The dual-mode optimally controlled photovoltaic power generation system of claim 1,
the second control module (32) is provided with a preset voltage range containing a lower limit voltage threshold and an upper limit voltage threshold; the second control module (32) of the second operating mode for setting the input voltage of the second conversion stage (31) at the threshold of the preset voltage range comprises
When the input-side real-time voltage of the second conversion stage (31) is greater than or equal to the upper limit voltage threshold, the second control module (32) fixedly sets the input voltage of the second conversion stage (31) at the upper limit voltage threshold; when the input-side real-time voltage of the second conversion stage (31) is less than or equal to the lower limit voltage threshold, the second control module (32) fixedly sets the input voltage of the second conversion stage (31) at the lower limit voltage threshold;
the first conversion stage (11) is a BUCK DC-DC conversion topology, the first control module (12) is configured to generate a pulse width modulated signal that controls the first conversion stage (11), and to adaptively set a duty cycle of the pulse width signal based on the tracked maximum power point input voltage of the first conversion stage (11) and based on a voltage parameter of the series connection (20) configured at the output of the first conversion stage (11); the second conversion stage (31) is a DC-AC inverter circuit, and the second control module (32) is used for performing inversion conversion within a rated regulation range of input voltage in a double closed loop mode by taking the meeting of the requirement of a power grid as a destination; -said second conversion stage (31) communicatively acquiring duty cycle data of said first conversion stage (11);
the preset optimization requirement is that the duty ratio data optimization reference range with the intermediate value between 0.8 and 0.95 is arranged, and the interval width of the optimization reference range is between 0.005 and 0.02.
9. A control method for a dual-mode optimized photovoltaic power generation system applying any one of claims 1 to 8, wherein the control method is applied to a photovoltaic power generation system comprising a second conversion stage (31) and a plurality of first conversion stages (11), each of the first conversion stages (11) having an input connected to a photovoltaic cell (90), outputs of the plurality of first conversion stages (11) being connected to each other to form a series circuit (20), and an input of the second conversion stage (31) being connected to an output of the series circuit (20), the control method comprising:
in each first conversion stage (11), tracking the maximum power point input voltage of the corresponding first conversion stage (11) respectively, and adaptively setting the duty ratio of the first conversion stage (11) according to the output voltage of the corresponding first conversion stage (11);
in each second conversion stage (31), when the input voltage of the second conversion stage (31) does not exceed the preset voltage range, setting the input voltage of the second conversion stage (31) in a first operation mode, and when the input voltage of the second conversion stage (31) exceeds the preset voltage range, setting the input voltage of the second conversion stage (31) in a second operation mode;
in the first operating mode, the input voltage of the second converter stage (31) is variably adjusted in order to satisfy a predetermined optimization requirement for the duty cycle data of the first converter stage (11), and the second operating mode is switched to when the input voltage of the second converter stage (31) exceeds a predetermined voltage range;
in the second operation mode, the input voltage of the second conversion stage (31) is set at the threshold value of the preset voltage range, and the input voltage of the second conversion stage (31) is adjusted to be within the preset voltage range until the duty ratio data of the first conversion stage (11) meet the preset tracking condition, so that the first operation mode is switched.
10. A photovoltaic inverter device of a dual-mode optimized photovoltaic power generation system applying any of the claims 1 to 8, characterized in that it comprises a second inverter stage (31) and a second control module (32), said second inverter stage (31) being of DC-AC conversion topology, said second inverter stage (31) being provided with a DC bus side for connection to a series line (20) formed by a plurality of first inverter stages (11) connected thereto;
when the input voltage of the second conversion stage (31) does not exceed the preset voltage range, the second control module (32) sets the input voltage of the second conversion stage (31) in a first operation mode, and when the input voltage of the second conversion stage (31) exceeds the preset voltage range, the second control module (32) sets the input voltage of the second conversion stage (31) in a second operation mode;
the second control module (32) of the first operating mode is used for variably adjusting the DC bus side voltage in order to enable the duty ratio data of the first conversion stage (11) to meet preset optimization requirements, and switching to the second operating mode until the DC bus side voltage exceeds a preset voltage range;
the second control module (32) of the second operating mode is configured to set the dc bus side voltage at a threshold of a preset voltage range; the second control module (32) of the second operation mode is further configured to adjust the dc bus side voltage to within a preset voltage range when the duty cycle data of the first conversion stage (11) satisfies a preset tracking condition, so as to switch to the first operation mode.
CN202111550141.7A 2021-12-17 2021-12-17 Dual-mode optimal control photovoltaic power generation system Pending CN114142525A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114614510A (en) * 2022-05-11 2022-06-10 深圳市中旭新能源有限公司 Photovoltaic module and power generation system are optimized to crisscross interconnection combination formula regional power
CN116154861A (en) * 2023-04-21 2023-05-23 深圳市中旭新能源有限公司 Photovoltaic system based on direct connection and power conversion dual-mode MLPE component

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114614510A (en) * 2022-05-11 2022-06-10 深圳市中旭新能源有限公司 Photovoltaic module and power generation system are optimized to crisscross interconnection combination formula regional power
CN114614510B (en) * 2022-05-11 2022-07-29 深圳市中旭新能源有限公司 Photovoltaic module and power generation system are optimized to crisscross interconnection combination formula regional power
CN116154861A (en) * 2023-04-21 2023-05-23 深圳市中旭新能源有限公司 Photovoltaic system based on direct connection and power conversion dual-mode MLPE component

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