CN108832651B - Control method and device of single-phase cascade type photovoltaic grid-connected inverter system - Google Patents

Control method and device of single-phase cascade type photovoltaic grid-connected inverter system Download PDF

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CN108832651B
CN108832651B CN201810394195.0A CN201810394195A CN108832651B CN 108832651 B CN108832651 B CN 108832651B CN 201810394195 A CN201810394195 A CN 201810394195A CN 108832651 B CN108832651 B CN 108832651B
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inverter
value
output voltage
voltage
phase
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CN108832651A (en
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粟梅
罗超
侯小超
韩华
原文宾
施光泽
孙尧
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Central South University
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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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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
    • 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
    • H02J3/40—Synchronising a generator for connection to a network or to another generator
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

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Abstract

The embodiment of the invention provides a control method and a device of a single-phase cascade type photovoltaic grid-connected inverter system, wherein the method comprises the following steps: detecting first local information of a first inverter and acquiring phase information of power grid voltage, controlling line current and the same phase of the power grid voltage according to the first local information and the phase information of the power grid voltage, and realizing MPPT operation; and for each second inverter, detecting second local information of the second inverter, controlling the output voltage of the second inverter to be in the same phase with the power grid voltage according to the line current and the second local information, and realizing MPPT operation. According to the embodiment of the invention, the local information of the first inverter is detected, the phase of the power grid voltage is obtained, the line current and the power grid voltage are controlled to be in the same phase, and the MPPT operation of all inverters is realized. Because only one communication line is needed to provide the phase information of the power grid voltage for the first inverter, the local information can be obtained through local detection, the system communication requirement is reduced, and the complexity of system control is reduced.

Description

Control method and device of single-phase cascade type photovoltaic grid-connected inverter system
Technical Field
The embodiment of the invention relates to the field of photovoltaic power generation, in particular to a control method and device of a single-phase cascade type photovoltaic grid-connected inverter system.
Background
With the development of industry and the increase of population, the consumption of traditional fossil energy by human beings is increasing day by day. And thus causes a series of environmental and social problems, such as environmental pollution, global warming, and energy crisis. Solar photovoltaic power generation is currently considered as a promising renewable energy power generation method which can replace traditional fossil energy.
The solar energy is a clean energy which has no pollution, wide distribution and easy acquisition. And the installation place of the photovoltaic power generation system is flexible, and the photovoltaic power generation system can be installed in a remote area to operate away from a network to form an autonomous regional power supply system so as to solve the problem of power supply in the remote area. Meanwhile, large-scale grid connection can be realized, and electric energy can be input into a large power grid for users to use. The large-scale photovoltaic grid-connected power generation is relatively applied. However, compared with most other power generation methods, the existing photovoltaic power generation technology has the defects of low energy conversion efficiency and high power generation cost. Therefore, how to improve the power generation efficiency and reduce the power generation cost are two major core problems of the current photovoltaic power generation. The configuration of power electronic interface converters in photovoltaic power generation systems and the control thereof are the most critical parts determining the energy conversion efficiency, reliability and power generation cost of photovoltaic power generation systems, and therefore are receiving more and more attention. An ideal photovoltaic power generation architecture should have low cost, high energy conversion efficiency, strong scalability, flexible controllability, and high reliability. In view of this, the single-phase cascaded photovoltaic grid-connected inverter system is regarded as a promising photovoltaic power generation framework.
In the related art, a single-phase cascaded photovoltaic grid-connected inverter system generally adopts centralized communication to obtain a grid synchronization signal. For a cascaded photovoltaic grid-connected inverter system with N cascaded photovoltaic inverters, at least N communication lines are needed to enable each inverter to obtain a power grid synchronization signal, and the defects that the reliability of the system is greatly restricted by communication and the control cost is high are caused by excessive communication lines. Particularly, when the single-phase cascade type photovoltaic grid-connected inverter system is applied to occasions of large-scale medium-voltage and high-voltage grid-connected fields, because each cascade type photovoltaic grid-connected system comprises a plurality of photovoltaic inverters, the reliability of the system is greatly reduced due to high communication complexity, and the control cost is greatly improved.
Disclosure of Invention
In order to solve the above problems, embodiments of the present invention provide a control method and apparatus for a single-phase cascade-type photovoltaic grid-connected inverter system, which overcome the above problems or at least partially solve the above problems.
According to a first aspect of the embodiments of the present invention, there is provided a control method for a single-phase cascade-type photovoltaic grid-connected inverter system, the method including:
detecting first local information of a first inverter, acquiring phase information of power grid voltage, controlling line current to be in phase with the power grid voltage according to the first local information and the phase information of the power grid voltage, and realizing MPPT operation of the first inverter;
and for each second inverter, detecting second local information of the second inverter, controlling the output voltage of the second inverter to be in the same phase with the grid voltage according to the line current and the second local information, and realizing MPPT operation of the second inverter.
According to the method provided by the embodiment of the invention, the MPPT operation of the first inverter is realized by detecting the first local information of the first inverter and acquiring the phase information of the power grid voltage, and controlling the line current and the power grid voltage to be in the same phase according to the first local information and the phase information of the power grid voltage; and for each second inverter, detecting second local information of the second inverter, controlling the output voltage of the second inverter to be in the same phase with the grid voltage according to the line current and the second local information, and realizing MPPT operation of the second inverter. Because the phase information of the power grid voltage is provided for the first inverter through only one communication line, other local information can be obtained through local detection, the system communication requirement is reduced, the complexity of system control is reduced, the control reliability is improved, and the control cost is reduced.
According to a second aspect of the embodiments of the present invention, there is provided a control apparatus for a single-phase cascade-type photovoltaic grid-connected inverter system, the apparatus including:
the first control module is used for detecting first local information of the first inverter, acquiring phase information of the power grid voltage, controlling the line current to be in phase with the power grid voltage according to the first local information and the phase information of the power grid voltage, and realizing MPPT operation of the first inverter;
and the second control module is used for detecting second local information of each second inverter, controlling the output voltage of the second inverter to be in the same phase with the grid voltage according to the line current and the second local information, and realizing MPPT operation of the second inverter.
According to a third aspect of the embodiments of the present invention, there is provided a control apparatus of a single-phase cascade-type photovoltaic grid-connected inverter system, including:
at least one processor; and
at least one memory communicatively coupled to the processor, wherein:
the memory stores program instructions executable by the processor, and the processor calls the program instructions to execute the control method of the single-phase cascade type photovoltaic grid-connected inverter system provided by any one of the various possible implementation manners of the first aspect.
According to a fourth aspect of the embodiments of the present invention, there is provided a non-transitory computer-readable storage medium storing computer instructions for causing a computer to execute the control method of the single-phase cascade-type photovoltaic grid-connected inverter system provided in any one of the various possible implementations of the first aspect.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of embodiments of the invention.
Drawings
Fig. 1 is a schematic flow chart of a control method of a single-phase cascade type photovoltaic grid-connected inverter system according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a single-phase cascade type photovoltaic grid-connected inverter system according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a first inverter of the single-phase cascade-type photovoltaic grid-connected inverter system according to the embodiment of the invention;
fig. 4 is a schematic structural diagram of a second inverter of the single-phase cascade-type photovoltaic grid-connected inverter system according to the embodiment of the invention;
fig. 5 is a flowchart illustrating a line current control method of the first inverter according to an embodiment of the present invention;
fig. 6 is a flowchart illustrating an output voltage control method of a second inverter according to an embodiment of the present invention;
fig. 7 is a schematic structural diagram of a control device of a single-phase cascade type photovoltaic grid-connected inverter system according to an embodiment of the present invention;
fig. 8 is a schematic structural diagram of a control device of a single-phase cascade type photovoltaic grid-connected inverter system according to an embodiment of the present invention;
fig. 9 is a schematic diagram of an output active power simulation result of a single-phase cascade type photovoltaic grid-connected inverter system including 3 inverters under a symmetric condition and a partial shielding condition according to an embodiment of the present invention;
fig. 10 is a schematic diagram of a simulation result of a steady-state output voltage of a single-phase cascade type photovoltaic grid-connected inverter system including 3 inverters under a symmetric condition and a partial shielding condition according to an embodiment of the present invention;
fig. 11 is a schematic diagram of a simulation result of a dc-side voltage of an inverter of a single-phase cascaded photovoltaic grid-connected inverter system including 3 inverters under a symmetric condition and a partially shielded condition according to an embodiment of the present invention;
fig. 12 is a schematic diagram of simulation results of steady-state line current and grid voltage of a single-phase cascade type photovoltaic grid-connected inverter system including 3 inverters under a symmetric condition and a partially shielded condition according to an embodiment of the present invention;
fig. 13 is a schematic diagram of an output active simulation result of the single-phase cascade type photovoltaic grid-connected inverter system including 3 inverters in the embodiment of the present invention under the condition that the voltage of the power grid drops by 10%;
fig. 14 is a schematic diagram of a steady-state output voltage simulation result of the single-phase cascade type photovoltaic grid-connected inverter system including 3 inverters according to the embodiment of the present invention under a condition that a grid voltage drops by 10%;
fig. 15 is a schematic diagram of a simulation result of a dc-side voltage of an inverter of the single-phase cascade type photovoltaic grid-connected inverter system including 3 inverters according to the embodiment of the present invention under a condition that a grid voltage drops by 10%;
fig. 16 is a schematic diagram of a simulation result of a steady-state line current and a grid voltage of a single-phase cascade type photovoltaic grid-connected inverter system including 3 inverters in the embodiment of the present invention under a condition that the grid voltage drops by 10%.
Detailed Description
The following describes embodiments of the present invention in further detail with reference to the drawings and examples. The following examples are intended to illustrate the examples of the present invention, but are not intended to limit the scope of the examples of the present invention.
The voltage of a point of common coupling of a single-phase cascaded photovoltaic grid-connected inverter system is the sum of the output voltages of all cascaded photovoltaic inverters, which enables a low-voltage photovoltaic inverter to be directly incorporated into a medium-voltage or high-voltage power grid through a low-voltage power electronic interface. Each cascaded photovoltaic inverter does not need a high-frequency isolation transformer to boost the direct-current voltage output by the photovoltaic panel, so that the system is low in loss and high in efficiency. Also, each cascaded photovoltaic inverter can be modularly mass produced. Compared with the traditional photovoltaic series centralized inverter framework, the single-phase cascade type photovoltaic grid-connected inverter system has higher reliability and more flexible expandability. This is because the inverters of the single-phase cascaded photovoltaic grid-connected inverter system are distributed, whereas the conventional photovoltaic string centralized inverter architecture is limited by the capacity of the centralized inverter and lacks redundancy. Compared with a multi-level cascade H-bridge framework which is widely applied, each inverter in the single-phase cascade photovoltaic grid-connected inverter system is provided with an independent output LC filter. The cascaded multi-level H bridge framework needs to adopt centralized communication to implement control, is constrained by the centralized communication, and has high control cost and low reliability. And each inverter output voltage in the single-phase cascade type photovoltaic grid-connected inverter system can be controlled at the frequency of a power grid, so that the realization of distributed and distributed control is facilitated, the system reliability is higher, and the control cost is low.
Aiming at the single-phase cascade type photovoltaic grid-connected inverter system, the embodiment of the invention provides a control method of the single-phase cascade type photovoltaic grid-connected inverter system. Referring to fig. 1, comprising:
101. the method comprises the steps of detecting first local information of a first inverter, obtaining phase information of power grid voltage, controlling line current to be in phase with the power grid voltage according to the first local information and the phase information of the power grid voltage, and achieving MPPT operation of the first inverter.
Referring to fig. 2, the single-phase cascade type photovoltaic grid-connected inverter system may include n single-phase H-bridge photovoltaic inverters connected in series, where n is a natural number greater than 1. The n series-connected single-stage photovoltaic inverters are connected to a large power grid via line impedances at a Point of Common Coupling (PCC). Each photovoltaic inverter comprises a local photovoltaic panel directly connected with a direct current input end of the photovoltaic inverter, a direct current side input filter capacitor, a single-phase H-bridge inverter and an output LC filter.
For the single-phase cascaded photovoltaic grid-connected inverter system of fig. 2, the one of the n series-connected inverters closest to the PCC is selected as the first inverter. The first inverter is controlled as a current source, and the first inverter is used as a reactive compensation unit to control or regulate the line current while realizing local photovoltaic panel Maximum Power Point Tracking (MPPT). The line current is controlled to enable the system to operate in a unit power factor grid-connected mode, and the line current and the grid voltage need to be in the same phase in the unit power factor grid-connected mode. In order to control the line current, it is necessary to detect the first local information and to obtain phase information of the grid voltage. The phase information may be obtained from the grid via a communication line, for example via a phase locked loop. And the first local information is obtained by detecting the first inverter and does not need to be obtained through networking communication. It should be noted that only phase information of the grid voltage needs to be obtained via the network.
102. And for each second inverter, detecting second local information of the second inverter, controlling the output voltage of the second inverter to be in the same phase with the grid voltage according to the line current and the second local information, and realizing MPPT operation of the second inverter.
For the single-phase cascade-type photovoltaic grid-connected inverter system shown in fig. 2, after one of n series-connected inverters is selected as a first inverter, all the remaining inverters are selected as second inverters, and the system at least includes one second inverter. All the second inverters are controlled to be voltage sources, MPPT is realized, and self-synchronization with the power grid voltage is realized, namely, the self-synchronization is the same phase and the same frequency with the power grid voltage. It should be noted that the second local information is similar to the first local information, and only the second inverter needs to be detected, and the grid synchronization signal does not need to be obtained.
According to the method provided by the embodiment of the invention, the MPPT operation of the first inverter is realized by detecting the first local information of the first inverter and acquiring the phase information of the power grid voltage, and controlling the line current and the power grid voltage to be in the same phase according to the first local information and the phase information of the power grid voltage; and for each second inverter, detecting second local information of the second inverter, controlling the output voltage of the second inverter to be in the same phase with the grid voltage according to the line current and the second local information, and realizing MPPT operation of the second inverter. Because the phase information of the power grid voltage is provided for the first inverter through only one communication line, other local information can be obtained through local detection, the system communication requirement is reduced, the complexity of system control is reduced, the control reliability is improved, and the control cost is reduced.
Based on the content of the above-mentioned embodiments, as an alternative embodiment, a line current control method of a first inverter is provided, and specifically, referring to fig. 2 and 5, the first local information includes a first dc-side photovoltaic panel output voltage value u of the first inverterdc1The output current value i of the first direct current side photovoltaic panelPV1And the actual value of the line current ig(ii) a Correspondingly, according to the phase information control line current of first local information and grid voltage in same phase to realize first inverter MPPT and move, include:
501. according to the output voltage value u of the photovoltaic panel on the first direct current sidedc1And a first DC side photovoltaic panel output current value iPV1Calculating a first DC-side voltage reference value of a first inverter
Figure GDA0002378977990000061
Specifically, the MPPT control unit of the first inverter may calculate
Figure GDA0002378977990000062
502. Outputting a voltage value u to the first direct current side photovoltaic paneldc1Regulated to a first DC-side voltage reference value
Figure GDA0002378977990000063
And using the current value obtained after regulation as the amplitude reference of the line current
Figure GDA0002378977990000064
Specifically, in order to realize active power balance between input and output of the first inverter and enable the first inverter to operate the MPPT, the output voltage u of the photovoltaic panel on the direct current side of the first inverter needs to be adjusteddc1Let u stand fordc1With the DC-side voltage reference of the first inverter generated by the MPPT control unit
Figure GDA0002378977990000071
Are equal.
503. The phase information of the power grid voltage is obtained through the communication line, and the reference value of the line current is obtained through synthesizing the amplitude reference of the line current and the phase information of the power grid voltage. Specifically, the phase information is the phase θgFor controlling the line current, the system is operated at unity power factor, the phase of the line current being referenced by the phase θ of the grid voltagegAnd (4) determining. Phase theta of the mains voltagegMay be communicated to the controller of the first inverter by a low bandwidth communication line. Amplitude reference of line current
Figure GDA0002378977990000072
Phase θ with the mains voltagegSynthesizing line current reference values
Figure GDA0002378977990000073
504. According to the actual value i of the line currentgWill beLine current regulation to line current reference value
Figure GDA0002378977990000074
In particular, the calculated line current reference value
Figure GDA0002378977990000075
The same phase with the line current, and the line current as the public quantity of the whole system can make the output current of each inverter be the same
Figure GDA0002378977990000076
Based on the content of the foregoing embodiments, as an optional embodiment, there is provided a method for obtaining a line current amplitude reference, specifically, adjusting a first dc-side photovoltaic panel output voltage value to a first dc-side voltage reference value, and taking a current value obtained after adjustment as an amplitude reference of a line current, including: outputting a voltage value u to the first direct current side photovoltaic paneldc1And a first DC side voltage reference value
Figure GDA0002378977990000077
Difference between them
Figure GDA0002378977990000078
Inputting the output of the DC voltage controller as the amplitude reference of the line current
Figure GDA0002378977990000079
The voltage u output by the photovoltaic panel on the direct current side of the first inverter isdc1And a first inverter DC side voltage reference value generated by the MPPT control unit
Figure GDA00023789779900000710
By subtraction of the difference between them
Figure GDA00023789779900000711
As an input to the first inverter dc voltage controller. The DC voltage controller is oneProportional-integral controller capable of tracking DC voltage reference value with zero error
Figure GDA00023789779900000712
And using the output of the DC voltage controller as the amplitude reference of the line current
Figure GDA00023789779900000713
Based on the content of the foregoing embodiments, as an optional embodiment, a line current adjusting method is provided, specifically, adjusting a line current to a line current reference value according to a line current actual value, including: the actual value i of the line currentgAnd line current reference value
Figure GDA00023789779900000714
Difference between them
Figure GDA00023789779900000715
The input current controller is a proportional resonant controller, and takes an output result of the current controller as an input signal of the pulse width modulation module; the input signal is input to a pulse width modulation module to generate a pulse signal for controlling the action of the switching device of the first inverter.
Wherein the current controller is a proportional resonant controller capable of tracking sinusoidal line current reference value with zero error
Figure GDA0002378977990000081
The output of the current controller is used as an input signal for a Pulse Width Modulation (PWM) module. The PWM module generates a switching pulse signal of the first inverter to control the action of a switching device of the first inverter, and the action of the switching device can realize the adjustment of line current and the MPPT operation of the first inverter.
Based on the content of the foregoing embodiment, as an alternative embodiment, there is provided an output voltage control method of the second inverter, and referring to fig. 3 and fig. 6, specifically, the second local information includes the second dc-side photovoltaic panel output voltage of the second inverterValue udciThe output current value i of the photovoltaic panel at the second direct current sidePViActual value u of output voltageiAnd the actual value of the line current ig(ii) a Correspondingly, the output voltage of the second inverter is controlled to be in phase with the grid voltage according to the line current and the second local information (it should be noted that the whole system includes a plurality of second inverters, only the ith second inverter is described below, the output voltage control methods of other second inverters are the same and are not described again, i is 2,3, …, n), and the MPPT operation of the second inverter is realized, including:
601. according to the output voltage value u of the photovoltaic panel at the second direct current sidedciAnd a second DC side photovoltaic panel output current value iPViCalculating a second DC-side voltage reference value of a second inverter
Figure GDA0002378977990000082
Specifically, the MPPT control unit of the second inverter calculates the DC side voltage reference value of the second inverter
Figure GDA0002378977990000083
602. Outputting a voltage value u to the second direct current side photovoltaic paneldciRegulated to a second DC-side voltage reference value
Figure GDA0002378977990000084
And obtaining the output voltage amplitude reference V of the second inverter after regulationi. Specifically, in order to realize active balance between input and output of the inverter and enable the second inverter to operate the MPPT, the output voltage u of the photovoltaic panel on the direct current side of the second inverter needs to be adjusteddciLet u stand fordciAnd a second inverter DC side voltage reference value generated by the MPPT control unit
Figure GDA0002378977990000085
Are equal. And the output active power balance of the second inverter is realized by adjusting the amplitude of the output voltage of the second inverter. The output voltage magnitude control expression of the second inverter can be expressed as:
Figure GDA0002378977990000086
wherein, ViRepresenting the output voltage amplitude reference of the second inverter, KPiAnd KIiRespectively representing a proportionality coefficient and an integral coefficient, V, of a DC-side voltage controller (proportional-integral controller) of the second invertergRepresenting the nominal grid voltage magnitude.
603. According to the actual value u of the output voltageiAnd the actual value of the line current igCalculating the sine value sin theta of the output power angle of the second inverteriAnd according to the sine value sin theta of the output power angleiCalculating an output voltage angular frequency reference omega of a second inverteri. Specifically, the actual value u of the output voltage of the second inverter is detected in real timeiAnd the actual value of the line current igCalculating the sine value sin theta of the output power angle of the second inverteriIt can be expressed as:
Figure GDA0002378977990000091
wherein, PiAnd QiIs the active and reactive power output by the second inverter.
To achieve self-synchronization of the second inverter with the grid voltage without communication, the output voltage angular frequency control expression of the second inverter can be expressed as:
ωi＝ω*+ki(sinθ*-sinθi)
wherein, ω isiRepresenting the second inverter output voltage angular frequency reference, ω*Representing nominal grid angular frequency, sin θ*Indicating the power angle reference value of the second inverter. In practical application, the photovoltaic grid-connected system is generally required to work at a unit power factor, so sin theta can be set*＝0。kiIs a self-synchronous control coefficient, k, of the second inverteriIs a normal number.
604. Reference omega to angular frequency of output voltageiIntegrating to obtain a second inverterOutput voltage phase reference deltaiAnd synthesizing an output voltage amplitude reference ViAnd an output voltage phase angle reference deltaiObtaining an output voltage reference value
Figure GDA0002378977990000092
605. According to the output voltage reference value
Figure GDA0002378977990000093
The output voltage of the second inverter is regulated.
Based on the content of the foregoing embodiments, as an optional embodiment, there is also provided an output voltage adjusting method of a second inverter, specifically, adjusting an output voltage of the second inverter according to an output voltage reference value, including: according to the output voltage reference value
Figure GDA0002378977990000094
Acquiring a modulation reference signal of a pulse width modulation module through voltage and current double closed-loop control; and inputting the modulation reference signal to a pulse width modulation module to generate a pulse signal for controlling the action of the second inverter switching device. Specifically, the PWM modulation module generates a switching pulse signal of the second inverter to control the switching device of the second inverter to operate, thereby regulating the output voltage to the output voltage reference value.
Based on the content of the foregoing embodiment, as an alternative embodiment, the first inverter is an inverter closest to the common coupling point among a plurality of inverters connected in series in the single-phase cascade type photovoltaic grid-connected inverter system. The first inverter is used as a current source, and can have a good current regulation effect when being closest to the common coupling point. Referring to fig. 2, inverter #1 from the point of common coupling serves as a first inverter, and inverter # i (i ═ 2,3, …, n) serves as a second inverter.
As shown in fig. 9 to 12, simulation results of the single-phase cascaded photovoltaic grid-connected inverter system including 3 inverters provided by the embodiment of the present invention under a symmetric condition and a partial shading condition are obtained. As shown in fig. 13 to 16, simulation results of a single-phase cascade-type photovoltaic grid-connected inverter system including 3 inverters provided by an embodiment of the present invention under a condition of grid voltage drop of 10% are shown.
Based on the content of the foregoing embodiments, an embodiment of the present invention provides a control device of a single-phase cascade-type photovoltaic grid-connected inverter system, where the control device of the single-phase cascade-type photovoltaic grid-connected inverter system is configured to execute the control method of the single-phase cascade-type photovoltaic grid-connected inverter system in the foregoing method embodiment. Referring to fig. 7, the apparatus includes:
the first control module 701 is configured to detect first local information of the first inverter and obtain phase information of the grid voltage, control a line current to be in phase with the grid voltage according to the first local information and the phase information of the grid voltage, and implement MPPT operation of the first inverter.
The first control module 701 controls the line current to operate the system in the unity power factor grid-connected mode, which requires the line current and the grid voltage to be in the same phase. In order to control the line current, the first control module 701 needs to detect the first local information and obtain the phase information of the grid voltage. The phase information may be obtained from the grid via a communication line, for example via a phase locked loop. The first local information is obtained by the first control module 701 detecting the first inverter, and is not obtained through networking communication. It should be noted that only phase information of the grid voltage needs to be obtained via the network.
The second control module 702 is configured to detect second local information of each second inverter, control an output voltage of the second inverter to be in phase with a grid voltage according to the line current and the second local information, and implement MPPT operation of the second inverter.
All the second inverters are controlled by the second control module 702 to be voltage sources, and realize the MPPT and the self-synchronization with the grid voltage, i.e. the self-synchronization is in phase and at the same frequency as the grid voltage. It should be noted that the second local information is similar to the first local information, and the second control module 702 only needs to detect the second inverter, and does not need to obtain the grid synchronization signal.
The device provided by the embodiment of the invention comprises: the first control module is used for detecting first local information of the first inverter, acquiring phase information of the power grid voltage, and controlling the line current to be in phase with the power grid voltage according to the first local information and the phase information of the power grid voltage; and the second control module is used for detecting second local information of each second inverter and controlling the output voltage of the second inverter to have the same frequency as the power grid voltage according to the line current and the second local information. Because the phase information of the power grid voltage is provided for the first inverter through only one communication line, other local information can be obtained through local detection, the system communication requirement is reduced, the complexity of system control is reduced, the control reliability is improved, and the control cost is reduced.
As an alternative embodiment, the first local information includes a first dc-side photovoltaic panel output voltage value, a first dc-side photovoltaic panel output current value, and a line current actual value of the first inverter; accordingly, the first control module comprises:
the first calculation unit is used for calculating a first direct current side voltage reference value of the first inverter according to the first direct current side photovoltaic panel output voltage value and the first direct current side photovoltaic panel output current value;
the current amplitude reference unit is used for adjusting the output voltage value of the first direct current side photovoltaic panel to be a first direct current side voltage reference value and taking the current value obtained after adjustment as the amplitude reference of the line current;
the first synthesis unit is used for acquiring phase information of the power grid voltage through a communication line and acquiring a line current reference value by synthesizing amplitude reference of line current and the phase information of the power grid voltage;
and the current adjusting unit is used for adjusting the line current to be the line current reference value according to the actual line current value.
As an alternative embodiment, the current amplitude reference unit is specifically configured to: and inputting the difference value between the output voltage value of the first direct current side photovoltaic panel and the first direct current side voltage reference value into a direct current voltage controller, and taking the output of the direct current voltage controller as the amplitude reference of the line current.
As an alternative embodiment, the current regulating unit is configured to:
inputting the difference value between the actual line current value and the reference line current value into a current controller, and taking the output result of the current controller as an input signal of a pulse width modulation module;
the input signal is input to a pulse width modulation module to generate a pulse signal for controlling the action of the switching device of the first inverter.
As an alternative embodiment, the second local information includes a second dc-side photovoltaic panel output voltage value, a second dc-side photovoltaic panel output current value, an output voltage actual value, and a line current actual value of the second inverter; accordingly, the second control module includes:
the second calculation unit is used for calculating a second direct-current side voltage reference value of the second inverter according to the second direct-current side photovoltaic panel output voltage value and the second direct-current side photovoltaic panel output current value;
the voltage amplitude reference unit is used for adjusting the output voltage value of the second direct current side photovoltaic panel to be a second direct current side voltage reference value and acquiring the output voltage amplitude reference of the second inverter after adjustment;
the third calculation unit is used for calculating the sine value of the output power angle of the second inverter according to the actual value of the output voltage and the actual value of the line current, and calculating the output voltage angular frequency reference of the second inverter according to the sine value of the output power angle;
the second synthesis unit is used for integrating the output voltage angular frequency reference to obtain an output voltage phase reference of the second inverter, and synthesizing an output voltage amplitude reference and an output voltage phase angle reference to obtain an output voltage reference value;
and the voltage regulating unit is used for regulating the output voltage of the second inverter according to the output voltage reference value.
As an alternative embodiment, the voltage regulating unit is specifically configured to:
acquiring a modulation reference signal of a pulse width modulation module through voltage and current double closed-loop control according to the output voltage reference value;
and inputting the modulation reference signal to a pulse width modulation module to generate a pulse signal for controlling the action of the second inverter switching device.
As an alternative embodiment, the first inverter is an inverter closest to the point of common coupling among a plurality of inverters connected in series in the single-phase cascade type photovoltaic grid-connected inverter system.
An embodiment of the present invention provides a control device for a single-phase cascade-type photovoltaic grid-connected inverter system, as shown in fig. 8, the control device includes: a processor (processor)801, a memory (memory)802, and a bus 803;
the processor 801 and the memory 802 communicate with each other via a bus 803; the processor 801 is configured to call up the program instructions in the memory 802 to execute the control method of the single-phase cascade-type photovoltaic grid-connected inverter system provided in the foregoing embodiment, and for example, the method includes:
detecting first local information of a first inverter, acquiring phase information of power grid voltage, and controlling line current to be in phase with the power grid voltage according to the first local information and the phase information of the power grid voltage;
and for each second inverter, detecting second local information of the second inverter, and controlling the output voltage of the second inverter to be in phase with the power grid voltage according to the line current and the second local information.
An embodiment of the present invention further provides a non-transitory computer-readable storage medium, where the non-transitory computer-readable storage medium stores computer instructions, and the computer instructions enable a computer to execute a control method of a single-phase cascade-type photovoltaic grid-connected inverter system provided in the corresponding embodiment, where the control method includes:
detecting first local information of a first inverter, acquiring phase information of power grid voltage, controlling line current to be in phase with the power grid voltage according to the first local information and the phase information of the power grid voltage, and realizing MPPT operation of the first inverter;
and for each second inverter, detecting second local information of the second inverter, controlling the output voltage of the second inverter to be in the same phase with the power grid voltage according to the line current and the second local information, and realizing MPPT operation of the second inverter.
Those of ordinary skill in the art will understand that: all or part of the steps for implementing the method embodiments may be implemented by hardware related to program instructions, and the program may be stored in a computer readable storage medium, and when executed, the program performs the steps including the method embodiments; and the aforementioned storage medium includes: various media that can store program codes, such as ROM, RAM, magnetic or optical disks.
The above-described embodiments of the control device of the single-phase cascade-type photovoltaic grid-connected inverter system and the like are merely illustrative, where units described as separate components may or may not be physically separate, and components displayed as units may or may not be physical units, that is, may be located in one place, or may also be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.
The method and the device provided by the embodiment of the invention greatly reduce the communication requirement, achieve the minimization and only need one low-bandwidth communication line; the system control complexity is greatly reduced, the influence of communication faults on the system is reduced, and the system reliability is greatly improved; the control cost of the system is greatly reduced; the method has a very promising prospect in large-scale medium and high voltage photovoltaic grid-connected occasions in the future.
Through the above description of the embodiments, those skilled in the art will clearly understand that each embodiment can be implemented by software plus a necessary general hardware platform, and certainly can also be implemented by hardware. With this understanding in mind, the above technical solutions may be embodied in the form of a software product, which can be stored in a computer-readable storage medium, such as ROM/RAM, magnetic disk, optical disk, etc., and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute the various embodiments or some parts of the methods of the embodiments.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (9)

1. A control method of a single-phase cascade type photovoltaic grid-connected inverter system is characterized by comprising the following steps:
detecting first local information of a first inverter and acquiring phase information of power grid voltage, controlling line current and the same phase of the power grid voltage according to the first local information and the phase information of the power grid voltage, and realizing MPPT operation;
for each second inverter, detecting second local information of the second inverter, controlling the output voltage of the second inverter to be in the same phase with the power grid voltage according to the line current and the second local information, and realizing MPPT operation;
the second local information comprises a second direct current side photovoltaic panel output voltage value, a second direct current side photovoltaic panel output current value, an output voltage actual value and a line current actual value of a second inverter;
correspondingly, the controlling the output voltage of the second inverter to be in phase with the grid voltage according to the line current and the second local information includes:
calculating a second direct current side voltage reference value of the second inverter according to the second direct current side photovoltaic panel output voltage value and the second direct current side photovoltaic panel output current value;
adjusting the output voltage value of the second direct current side photovoltaic panel to a second direct current side voltage reference value, and obtaining the output voltage amplitude reference of the second inverter after adjustment;
calculating the sine value of the output power angle of the second inverter according to the actual value of the output voltage and the actual value of the line current, and calculating the output voltage angular frequency reference of the second inverter according to the sine value of the output power angle;
integrating the output voltage angular frequency reference to obtain an output voltage phase reference of the second inverter, and synthesizing an output voltage amplitude reference and an output voltage phase angle reference to obtain an output voltage reference value;
and regulating the output voltage of the second inverter according to the output voltage reference value.
2. The method of claim 1, wherein the first inverter is one of a plurality of series-connected inverters of a single-phase cascaded photovoltaic grid-connected inverter system that is closest to a point of common coupling; the second inverter is each of the plurality of inverters connected in series of the single-phase cascade-type photovoltaic grid-connected inverter system except the first inverter.
3. The method of claim 1, wherein the first local information includes a first dc-side photovoltaic panel output voltage value, a first dc-side photovoltaic panel output current value, and a line current actual value for the first inverter;
correspondingly, the controlling the line current to be in phase with the grid voltage according to the first local information and the phase information of the grid voltage, and realizing the operation of the first inverter MPPT includes:
calculating a first direct current side voltage reference value of the first inverter according to the first direct current side photovoltaic panel output voltage value and the first direct current side photovoltaic panel output current value;
adjusting the output voltage value of the first direct current side photovoltaic panel to be a first direct current side voltage reference value, and taking the current value obtained after adjustment as the amplitude reference of the line current;
acquiring phase information of the power grid voltage through a communication line, and acquiring a line current reference value by synthesizing amplitude reference of the line current and the phase information of the power grid voltage;
and adjusting the line current to the line current reference value according to the actual line current value.
4. The method according to claim 3, wherein the adjusting the first DC-side photovoltaic panel output voltage value to a first DC-side voltage reference value and using the current value obtained after the adjusting as the amplitude reference of the line current comprises:
and inputting the difference value between the output voltage value of the first direct current side photovoltaic panel and the first direct current side voltage reference value into a direct current voltage controller, wherein the direct current voltage controller is a proportional-integral controller, and the output of the direct current voltage controller is used as the amplitude reference of the line current.
5. The method of claim 3, wherein adjusting the line current to the line current reference value based on the line current actual value comprises:
inputting a difference value between a line current actual value and a line current reference value into a current controller, wherein the current controller is a proportional resonant controller, and an output result of the current controller is used as an input signal of a pulse width modulation module;
the input signal is input to a pulse width modulation module to generate a pulse signal for controlling the action of the switching device of the first inverter.
6. The method of claim 1, wherein the adjusting the output voltage of the second inverter based on the output voltage reference comprises:
acquiring a modulation reference signal of a pulse width modulation module through voltage and current double closed-loop control according to the output voltage reference value;
and inputting the modulation reference signal to a pulse width modulation module to generate a pulse signal for controlling the action of the second inverter switching device.
7. A control device of a single-phase cascade type photovoltaic grid-connected inverter system is characterized by comprising:
the first control module is used for detecting first local information of the first inverter, acquiring phase information of the power grid voltage, controlling the line current to be in phase with the power grid voltage according to the first local information and the phase information of the power grid voltage, and realizing MPPT operation of the first inverter;
the second control module is used for detecting second local information of each second inverter, controlling the output voltage of the second inverter to be in the same phase with the grid voltage according to the line current and the second local information, and realizing MPPT operation of the second inverter;
the second local information comprises a second direct current side photovoltaic panel output voltage value, a second direct current side photovoltaic panel output current value, an output voltage actual value and a line current actual value of a second inverter;
correspondingly, the second control module is specifically configured to:
calculating a second direct current side voltage reference value of the second inverter according to the second direct current side photovoltaic panel output voltage value and the second direct current side photovoltaic panel output current value;
adjusting the output voltage value of the second direct current side photovoltaic panel to a second direct current side voltage reference value, and obtaining the output voltage amplitude reference of the second inverter after adjustment;
calculating the sine value of the output power angle of the second inverter according to the actual value of the output voltage and the actual value of the line current, and calculating the output voltage angular frequency reference of the second inverter according to the sine value of the output power angle;
integrating the output voltage angular frequency reference to obtain an output voltage phase reference of the second inverter, and synthesizing an output voltage amplitude reference and an output voltage phase angle reference to obtain an output voltage reference value;
and regulating the output voltage of the second inverter according to the output voltage reference value.
8. A control device of a single-phase cascade type photovoltaic grid-connected inverter system, characterized by comprising:
at least one processor;
and at least one memory communicatively coupled to the processor, wherein:
the memory stores program instructions executable by the processor, the processor invoking the program instructions to perform the method of any of claims 1 to 6.
9. A non-transitory computer-readable storage medium storing computer instructions that cause a computer to perform the method of any one of claims 1 to 6.
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