CN113872209A - Single-phase photovoltaic grid-connected control method for eliminating direct-current bus voltage sampling ripple - Google Patents

Single-phase photovoltaic grid-connected control method for eliminating direct-current bus voltage sampling ripple Download PDF

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CN113872209A
CN113872209A CN202111304029.5A CN202111304029A CN113872209A CN 113872209 A CN113872209 A CN 113872209A CN 202111304029 A CN202111304029 A CN 202111304029A CN 113872209 A CN113872209 A CN 113872209A
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grid
inverter
voltage
current
current bus
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CN113872209B (en
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郭晓瑞
杜树新
金建祥
荀倩
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Huzhou 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
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • 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
    • 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
    • Y02E40/40—Arrangements for reducing harmonics

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Abstract

A single-phase photovoltaic grid-connected control method for eliminating direct-current bus voltage sampling ripples. Step 1: performing mathematical modeling on the inverter, converting the inverter into equivalent impedance, and step 2: unique voltage V at two ends of direct current bus capacitor of control sampling grid-connected inverterdcA secondary voltage ripple compensation elimination algorithm is adopted in the loop, and the step 3 is as follows: by introducing mains voltage Vgsin ω t to obtain an inverter bridge grid-connected current reference protocol iref(ii) a Step 4: collecting the inductive current of the grid-connected inverter and comparing irefAnd then, the output of the grid-connected inverter is controlled after PWM distribution is carried out by sending the output to a current loop PI controller, and the method completely eliminates ripples on sampling voltage by introducing a virtual secondary ripple of a capacitor on a direct current bus of a secondary voltage harmonic generator, thereby reducing the total harmonic distortion of grid-connected current on the basis of not obviously increasing the circuit cost of the inverter.

Description

Single-phase photovoltaic grid-connected control method for eliminating direct-current bus voltage sampling ripple
Technical Field
The device relates to the field of application of photovoltaic power generation system control technology, in particular to a single-phase photovoltaic grid-connected control method for eliminating direct-current bus voltage sampling ripples.
Background
In recent years, the problems of energy shortage and environmental pollution are widely concerned by people, and new energy power generation systems such as photovoltaic power generation and wind power generation become hot spots of current vigorous research in academia and industry due to the advantages of cleanness, high efficiency, sustainability and the like, and a series of schemes and products are provided.
In a traditional single-phase photovoltaic grid-connected inverter system, since the output Power of a photovoltaic solar array is affected by the illumination intensity to a great extent, in order to improve the utilization efficiency of the photovoltaic array and ensure that the photovoltaic array can continuously output with the Maximum Power, Maximum Power Point Tracking (MPPT) is required.
For the new energy power generation system, the output power of the grid-connected inverter contains power ripples with the frequency twice as high as the voltage frequency of a power grid, and the power ripples are necessarily fed back to a direct current power source end, so that the input current contains a large number of ripple components, and for a photovoltaic assembly, the maximum power point tracking of the photovoltaic assembly is influenced, and the system efficiency is reduced. In the prior art, the Chinese authorized public number: CN108111037B a zero input ripple inverter and its control method, adding a decoupling circuit composed of decoupling switch tube, decoupling diode, decoupling inductance and decoupling capacitance and adding transformer auxiliary winding on the primary side of the isolation transformer, the grid voltage sampling value gets the sine wave with same frequency and phase with it through PLL, the input voltage and current sampling value gets the maximum DC input power through MPPT, then gets five modulation wave signals through the reference generation module and modulation wave generation module, finally through comparator and logic circuit, thus controlling the grid-connected inverter to work. According to the scheme, a decoupling circuit and an auxiliary winding are added, so that the cost is increased; on the other hand, the performance requirements of the five modulated wave signals on a distributed controller and other computer controllers are high during comparison and logic control, so that the control method is based on hardware supplement and has the effect of eliminating ripples, but the convenience is not high, and the transplantation applicability is low.
Therefore, how to utilize the powerful data processing capacity of a computer, eliminate the sampling ripple on the voltage of the direct current bus and improve the reference quality of the grid-connected current so as to reduce the Total Harmonic Distortion (THD) of the grid-connected current and realize a convenient signal sampling and control method to solve the ripple problem of the new energy power generation system has very important significance.
Disclosure of Invention
In order to solve the problems in the prior art, the invention designs a method for preventing commercial power energy from flowing backwards, and ensures the safety of a UPS and the stable operation of a load.
The technical scheme of the invention is as follows: the method is realized in a digital signal processor DSP according to the following steps:
step 1: the inverter is equivalent to a resistor R and a direct current bus capacitor C which are connected in parallel,
Figure BDA0003339473750000011
c: the capacitance value of a DC end direct current bus capacitor of the photovoltaic single-phase grid-connected inverter DC/AC;
r: the equivalent output resistance of the grid-connected inverter,
Figure BDA0003339473750000021
where η is the efficiency of the grid-connected inverter, Vpv、ipvRespectively inputting the input voltage and the input current of the solar panel to the single-phase grid-connected inverter; t is the mains supply period;
step 2: voltage V at two ends of direct-current bus capacitor of acquisition grid-connected inverterdcSaid V isdcThe method also comprises a capacitance secondary ripple on a direct current bus of the algorithm virtual secondary voltage harmonic generator:
Figure BDA0003339473750000022
wherein Vdc_refIs VdcSaid reference value, said VdcAnd then with the reference value Vdc_refComparing to obtain Vdc_verrThe output V is calculated after being sent into a voltage loop PI controllerm；
And step 3: by introducing mains voltage Vgsin ω t, so that the inverter bridge grid-connected current reference protocol is as follows:
Figure BDA0003339473750000023
wherein the content of the first and second substances,
Figure BDA0003339473750000024
is VmThe direct current component of the electric current is,
Figure BDA0003339473750000025
Figure BDA0003339473750000026
is VmAn alternating current component of double frequency;
step 4: collecting inductive current i of grid-connected inverterL，iLAnd irefAnd after comparison, sending the comparison result to a current loop PI controller, and controlling a grid-connected inverter after PWM distribution.
In summary, compared with the prior art, the invention has the beneficial effects that:
in the voltage and current closed-loop control scheme in the prior art, mathematical modeling is carried out on an inverter, the inverter is converted into equivalent impedance, a secondary voltage ripple compensation elimination algorithm is uniquely adopted in a control sampling loop, and the secondary ripple of a capacitor on a direct current bus of a virtual secondary voltage harmonic generator is introduced to completely eliminate sampling voltage VdcThe total harmonic distortion of the grid-connected current is reduced on the basis of not obviously increasing the cost of the inverter circuit.
Drawings
FIG. 1: the invention relates to a single-phase grid-connected inverter framework
FIG. 2: schematic of data processing for the method of the invention.
FIG. 3: mains voltage V at the same time axisgsin ω t, calculation output V of voltage loop PI controllermInverse bridge grid-connected current reference protocol irefThe waveform comparison between the two figures.
FIG. 4: the effect comparison chart of the grid-connected waveform before and after the control by using the method of the invention.
Detailed Description
According to the single-phase grid-connected inverter architecture as shown in FIG. 1, the capacitor CpvThe front-end BOOST circuit is connected with the solar panel in parallel and adopts a maximum power tracking algorithm to control the output voltage V of the preceding-stage photovoltaic panelpv(ii) a The output current of the battery panel is ipv，VpvAnd ipvThe product of (a) is the output power of the solar panel. L isb、Qb、DbAnd C is an inductor, a switching tube, a fast recovery fly-wheel diode and an output capacitor of the BOOST circuit respectively. The voltage and the output current at two ends of the output capacitor are respectively VdcAnd Io。Vgsin ω t denotes the mains voltage, where VgAnd ω represents the amplitude and fundamental angular frequency of the mains, respectively. Because the mains voltage and the output grid-connected current are in the same phase when the grid-connected inverter is output, the grid-connected inverter can be equivalent to a resistive load R.
Firstly, the inverter is equivalently converted into parallel connection of a resistor R and a direct current bus capacitor C, and the method comprises the following steps:
when the inverter is connected to the grid, the grid current iacThe required voltage is equal to the mains voltage Vgsin ω t are in phase. Vgsin ω t has a waveform V as shown in FIG. 3gIs the amplitude of the mains voltage, if the mains voltage has an effective value of 220V, then V isgIt is 311V. Thus setting the grid-connected current iac＝αVgsin ω t, then the instantaneous power of the grid is
Figure BDA0003339473750000031
Figure BDA0003339473750000032
Figure BDA0003339473750000033
Because the instantaneous power delivered to the grid when the inverter is connected to the grid is
Figure BDA0003339473750000034
Is a component containing DC power
Figure BDA0003339473750000035
And a secondary AC power component
Figure BDA0003339473750000036
The power transmitted to the direct current bus capacitor C by the solar cell panel is a direct current component, and the voltage V at two ends of the direct current bus capacitor is constant according to energy conservationdcContains twice the frequency of the ac component.
According to the AC side feedback control loop of the grid-connected inverter shown in FIG. 2, the DC bus voltage is referenced Vdc_refIs a direct current component, Vdc_verrWill inevitably also contain a double frequency voltage ripple component, so that the calculated output V via the voltage loop PI controllermIn addition to containing a direct current component
Figure BDA0003339473750000037
In addition, it will also contain a frequency-doubled AC component
Figure BDA0003339473750000038
Can be written as
Figure BDA0003339473750000039
The inverter bridge grid-connected current reference protocol is written as:
Figure BDA00033394737500000310
the waveform is shown in fig. 3, the inductor current can generally accurately track the current reference, so that the instantaneous power output by the inverter bridge is as follows:
Figure BDA00033394737500000311
its average power can be written as:
Figure BDA0003339473750000041
Figure BDA0003339473750000042
due to VdcThe voltage ripple is contained, and the DC bus voltage reference V can be useddc_refInstead of this.
Then:
Figure BDA0003339473750000043
Figure BDA0003339473750000044
Figure BDA0003339473750000045
the inverter can be equivalent to a virtual resistor R and a direct-current bus capacitor C which are connected in parallel, and the equivalent impedance Z obtained after the virtual resistor R and the direct-current bus capacitor C are connected in parallel is as follows:
Figure BDA0003339473750000046
c, capacitance value of a DC end direct current bus capacitor of the photovoltaic single-phase grid-connected inverter DC/AC;
r is the equivalent output resistance of the grid-connected inverter,
Figure BDA0003339473750000047
where η is the efficiency of the grid-connected inverter, Vpv、ipvRespectively inputting the input voltage and the input current of the solar panel to the single-phase grid-connected inverter; t is the mains supply period; if the commercial power is 50Hz, T is 0.02 s; vdc_refAnd omega is the angular frequency, if in the 50Hz frequency band, omega is 100 pi rad/s, and if in the 100Hz frequency band, omega is 200 pi rad/s.
A secondary voltage ripple compensation elimination algorithm is adopted in the sampling loop to completely eliminate the sampling voltage VdcSo that the voltage loop PI control output can be ensured
Figure BDA0003339473750000048
Thus the above equation can be rewritten as:
Figure BDA0003339473750000049
Figure BDA0003339473750000051
the capacitance secondary ripple on the dc bus can be written as:
Figure BDA0003339473750000052
wherein io2Is the direct current bus second harmonic current.
Figure BDA0003339473750000053
Due to the fact that
Figure BDA0003339473750000054
Then merging to obtain:
Figure BDA0003339473750000055
wherein
Figure BDA0003339473750000056
Also due to VdcThe voltage ripple is contained, and the DC bus voltage reference V can be useddc_refInstead of this.
Figure BDA0003339473750000057
As shown in fig. 4, the grid-connected voltage waveforms before and after the improvement are compared, and the output waveform of the grid-connected inverter bridge becomes smooth after the improvement, so that the THD is greatly reduced.
The foregoing shows and describes the general principles, essential 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 given by way of illustration of the principles of the present invention, and that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (1)

1. A single-phase photovoltaic grid-connected control method for eliminating direct-current bus voltage sampling ripples is characterized by comprising the following steps: the method is realized in a Digital Signal Processor (DSP) according to the following steps:
step 1: the inverter is equivalent to a resistor R and a direct current bus capacitor C which are connected in parallel,
Figure FDA0003339473740000011
c: the capacitance value of a DC end direct current bus capacitor of the photovoltaic single-phase grid-connected inverter DC/AC;
r: the equivalent output resistance of the grid-connected inverter,
Figure FDA0003339473740000017
where η is the efficiency of the grid-connected inverter, Vpv、ipvRespectively inputting the input voltage and the input current of the solar panel to the single-phase grid-connected inverter; t is the mains supply period;
step 2: voltage V at two ends of direct-current bus capacitor of acquisition grid-connected inverterdcSaid V isdcAlso comprising an algorithm virtualAnd (3) secondary ripple of a capacitor on a direct current bus of the secondary voltage harmonic generator:
Figure FDA0003339473740000012
wherein Vdc_refIs VdcSaid reference value, said VdcAnd then with the reference value Vdc_refComparing to obtain Vdc_verrThe output V is calculated after being sent into a voltage loop PI controllerm；
And step 3: by introducing mains voltage Vgsin ω t, so that the inverter bridge grid-connected current reference protocol is as follows:
Figure FDA0003339473740000013
wherein the content of the first and second substances,
Figure FDA0003339473740000014
is VmThe direct current component of the electric current is,
Figure FDA0003339473740000015
Figure FDA0003339473740000016
is VmAn alternating current component of double frequency;
step 4: collecting inductive current i of grid-connected inverterL，iLAnd irefAnd after comparison, sending the comparison result to a current loop PI controller, performing PWM distribution, and controlling the output of the grid-connected inverter.
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Cited By (1)

* Cited by examiner, † Cited by third party
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