CN107465191B - Photovoltaic power station DC/DC-DC/AC harmonic control method - Google Patents
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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
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- 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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- 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
The invention provides a photovoltaic power station DC/DC-DC/AC harmonic control method, wherein a DC/DC chopper circuit and an inverter are sequentially arranged between a DC output end of a photovoltaic power station and a power grid, and the DC/DC chopper circuit is triggered by an SPWM trigger; acquiring the output voltage of a photovoltaic array of a photovoltaic power station; obtaining a trigger angle corresponding to each trigger moment, and determining the trigger time of the SPWM of the photovoltaic power station; determining the output voltage of a chopper circuit of a DC/DC chopper circuit; calculating harmonic voltage output by the inverter; calculating the harmonic content percentage of the photovoltaic power station according to the output voltage of a chopper circuit of the DC/DC chopper circuit and the harmonic voltage output by the inverter; judging the percentage of the harmonic content of the current photovoltaic power station, and determining that the DC/DC-DC/AC harmonic control process of the photovoltaic power station meets the requirements. The invention improves the traditional inverter, and performs corresponding chopping on direct current generated by photovoltaic, thereby effectively weakening the content of each subharmonic.
Description
Technical Field
The invention belongs to the technical field of power grids, and particularly relates to a photovoltaic power station DC/DC-DC/AC harmonic control method.
Background
The method has the advantages that the requirement on the quality of electricity is high when the photovoltaic power station is connected to the grid, the traditional inverter adopts the SPWM technology, sine waves are equivalent to a series of pulse waveforms with equal time intervals, the required sine waves are formed by controlling the IGBT conducting time, the method can inhibit low-order harmonic waves of the inverter and possibly output harmonic wave components with the frequency related to carrier waves, the harmonic wave components can be effectively reduced by utilizing the harmonic wave inhibition method of DC/DC-DC/AC due to the fact that the output voltage of a photovoltaic array is unstable, stable direct-current voltage can be output, and the quality of electric energy is greatly improved.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a photovoltaic power station DC/DC-DC/AC harmonic control method.
A photovoltaic power station DC/DC-DC/AC harmonic control method comprises the following steps:
step 1: a DC/DC chopper circuit and an inverter are sequentially arranged between a direct current output end of a photovoltaic power station and a power grid, and the DC/DC chopper circuit is triggered through an SPWM trigger;
step 2: obtaining photovoltaic array output voltage U of photovoltaic power stationgEstablishing a relational expression between voltage values of different trigger moments of the DC/DC chopper circuit and trigger angles corresponding to the trigger moments to obtain the trigger angles corresponding to the trigger moments, so as to determine the trigger time of the SPWM of the photovoltaic power station;
the relation between the voltage values at different trigger moments of the DC/DC chopper circuit and the corresponding trigger angles at the trigger moments is established as follows:
first trigger time voltage u of DC/DC chopper circuit1Firing angle α corresponding to a first firing time1The relationship of (A) is as follows:
wherein u ist=Ug,α2For the second triggering moment corresponding to the triggering angle, α4The fourth trigger moment corresponds to a trigger angle;
third trigger time voltage u of DC/DC chopper circuit3Firing angle α corresponding to third firing time3The relationship of (A) is as follows:
voltage u at fifth trigger time of DC/DC chopper circuit5Firing angle α corresponding to the fifth firing time5The relationship of (A) is as follows:
seventh trigger time voltage u of DC/DC chopper circuit7Firing angle α corresponding to the seventh firing time7The relationship of (A) is as follows:
ninth trigger time voltage u of DC/DC chopper circuit9Firing angle α corresponding to ninth firing time9The relationship of (A) is as follows:
and step 3: triggering a DC/DC chopper circuit at the determined triggering time of the SPWM of the photovoltaic power station according to the photovoltaic array output voltage U of the photovoltaic power stationgDetermining an output voltage U of a chopper circuit of a DC/DC chopper circuitd0;
According to the output voltage U of the photovoltaic array of the photovoltaic power stationgDetermining an output voltage U of a chopper circuit of a DC/DC chopper circuitd0The calculation formula of (a) is as follows:
where n is 6k, · and ∞, k is 1,2,. and ∞, and ω is the fundamental frequency.
And 4, step 4: according to the frequency modulation ratio N of the inverter, the amplitude modulation ratio M of the inverter and the photovoltaic array output voltage U of the photovoltaic power stationgCalculating harmonic voltage U output by inverterxh1;
The frequency modulation ratio N according to the inverter, the amplitude modulation ratio M according to the inverter and the photovoltaic array output voltage U of the photovoltaic power stationgCalculating harmonic voltage U output by inverterxh1The calculation formula of (a) is as follows:
wherein m is the number of harmonics,fcis a carrier frequency, fmFor modulating the wave frequency, MmIs the carrier amplitude, McIn order to modulate the amplitude of the wave,for the second harmonic initial phase, n is 6k,., ∞, k is 1,2.,. and infinity, and ω is the fundamental frequency.
And 5: according to the output voltage U of the chopper circuit of the DC/DC chopper circuitd0And harmonic voltage U of inverter outputxh1Calculating the harmonic content percentage upsilon of the photovoltaic power station;
the calculation formula of the photovoltaic power station harmonic content percentage upsilon is as follows:
step 6: and judging whether the harmonic content percentage upsilon of the current photovoltaic power station is smaller than or equal to a threshold value of the harmonic content percentage, if so, enabling the DC/DC-DC/AC harmonic control process of the current photovoltaic power station to meet the requirement, otherwise, adjusting corresponding trigger angles of all trigger moments of the DC/DC chopper circuit, determining the trigger time of the SPWM of the photovoltaic power station, and returning to the step 3.
The threshold for the percentage of harmonic content is 10%.
The invention has the beneficial effects that:
the invention provides a photovoltaic power station DC/DC-DC/AC harmonic control method, which improves the traditional inverter, adds a DC/DC converter in front of an inverter, performs corresponding chopping on direct current generated by photovoltaic to change the direct current into direct current with another fixed voltage, performs corresponding SPWM conversion on the direct current with the fixed voltage, and can effectively weaken the content of each subharmonic.
Drawings
FIG. 1 is a block flow diagram of a DC/DC-DC/AC harmonic control method for a photovoltaic power plant in the present embodiment;
fig. 2 is a block diagram of an apparatus structure of a photovoltaic power station DC/DC-DC/AC harmonic control method according to an embodiment of the present invention.
Detailed Description
The following detailed description of embodiments of the invention refers to the accompanying drawings.
In the embodiment, a certain photovoltaic power station adopts 36V cell panels, and the number of the cell panels in series connection and parallel connection is 10 and 100; therefore, the output voltage U of the photovoltaic array of the photovoltaic power station can be calculatedgThe voltage is 360V, the amplitude modulation ratio M of the inverter is 0.8, the frequency modulation ratio N of the inverter is 40, and the output fundamental frequency omega is 50 Hz.
A method for controlling a photovoltaic power plant DC/DC-DC/AC harmonic, as shown in fig. 1, comprises the following steps:
step 1: a DC/DC chopper circuit and an inverter are sequentially arranged between a direct-current output end of a photovoltaic power station and a power grid, and the DC/DC chopper circuit is triggered through an SPWM trigger, as shown in figure 2.
Step 2: obtaining photovoltaic array output voltage U of photovoltaic power stationgAnd establishing a relational expression between voltage values of the DC/DC chopper circuit at different trigger moments and trigger angles corresponding to the trigger moments to obtain the trigger angles corresponding to the trigger moments, so as to determine the trigger time of the SPWM of the photovoltaic power station.
In the present embodiment, a relational expression between voltage values at different trigger times of the DC/DC chopper circuit and trigger angles corresponding to the trigger times is established as follows:
first trigger time voltage u of DC/DC chopper circuit1Firing angle α corresponding to a first firing time1Is represented by the formula (1):
wherein u ist=Ug,α2For the second triggering moment corresponding to the triggering angle, α4The fourth trigger time corresponds to the trigger angle.
Third trigger time voltage u of DC/DC chopper circuit3Firing angle α corresponding to third firing time3Is represented by the formula (2):
voltage u at fifth trigger time of DC/DC chopper circuit5Firing angle α corresponding to the fifth firing time5Is represented by the formula (3):
seventh trigger time voltage u of DC/DC chopper circuit7Firing angle α corresponding to the seventh firing time7Is represented by the formula (4):
ninth trigger time voltage u of DC/DC chopper circuit9Firing angle α corresponding to ninth firing time9Is represented by the formula (5):
let the first trigger time voltage u of the DC/DC chopper circuit1Equal to the output voltage U of the photovoltaic array of the photovoltaic power stationgLet the voltage u at the third trigger time of the DC/DC chopper circuit3Voltage u at the fifth trigger time5Voltage u at the seventh trigger time7Voltage u at the ninth trigger time9Equal to 0, resulting in the equations (6) - (10):
and step 3: triggering a DC/DC chopper circuit at the determined triggering time of the SPWM of the photovoltaic power station according to the photovoltaic array output voltage U of the photovoltaic power stationgDetermining an output voltage U of a chopper circuit of a DC/DC chopper circuitd0。
In the embodiment, the voltage U is output according to the photovoltaic array of the photovoltaic power stationgDetermining an output voltage U of a chopper circuit of a DC/DC chopper circuitd0Is represented by equation (11):
where n is 6k, · and ∞, k is 1,2,. and ∞, and ω is the fundamental frequency.
And 4, step 4: according to the frequency modulation ratio N of the inverter, the amplitude modulation ratio M of the inverter and the photovoltaic array output voltage U of the photovoltaic power stationgCalculating harmonic voltage U output by inverterxh1。
In the embodiment, the frequency modulation ratio N of the inverter, the amplitude modulation ratio M of the inverter and the photovoltaic array output voltage U of the photovoltaic power station are usedgCalculating harmonic voltage U output by inverterxh1Is represented by equation (12):
wherein m is the number of harmonics,fcis a carrier frequency, fmFor modulating the wave frequency, MmIs the carrier amplitude, McIn order to modulate the amplitude of the wave,for the second harmonic initial phase, n is 6k,., ∞, k is 1,2.,. and infinity, and ω is the fundamental frequency.
And 5: according to the output voltage U of the chopper circuit of the DC/DC chopper circuitd0And harmonic voltage U of inverter outputxh1And calculating the harmonic content percentage upsilon of the photovoltaic power station.
In the embodiment, a calculation formula of the percentage υ of the harmonic content of the photovoltaic power station is shown as a formula (14):
step 6: and judging whether the harmonic content percentage upsilon of the current photovoltaic power station is smaller than or equal to a threshold value of the harmonic content percentage, if so, enabling the DC/DC-DC/AC harmonic control process of the current photovoltaic power station to meet the requirement, otherwise, adjusting corresponding trigger angles of all trigger moments of the DC/DC chopper circuit, accordingly determining the trigger time of the SPWM of the photovoltaic power station, and returning to the step 23.
In the embodiment, the threshold value of the harmonic content percentage is 10%, as upsilon is 8.17% < 10%, the current photovoltaic power station DC/DC-DC/AC harmonic control process meets the requirement. Otherwise, adjusting the voltage u at the third trigger moment of the DC/DC chopper circuit3Voltage u at the fifth trigger time5Voltage u at the seventh trigger time7Voltage u at the ninth trigger time9And (3) adjusting the trigger angle corresponding to each trigger moment of the DC/DC chopper circuit, determining the trigger time of the photovoltaic power station SPWM and returning to the step 3.
Claims (4)
1. A photovoltaic power station DC/DC-DC/AC harmonic control method is characterized by comprising the following steps:
step 1: a DC/DC chopper circuit and an inverter are sequentially arranged between a direct current output end of a photovoltaic power station and a power grid, and the DC/DC chopper circuit is triggered through an SPWM trigger;
step 2: obtaining photovoltaic array output voltage U of photovoltaic power stationgEstablishing a relational expression between voltage values of different trigger moments of the DC/DC chopper circuit and trigger angles corresponding to the trigger moments to obtain the trigger angles corresponding to the trigger moments, so as to determine the trigger time of the SPWM of the photovoltaic power station;
and step 3: triggering a DC/DC chopper circuit at the determined triggering time of the SPWM of the photovoltaic power station according to the photovoltaic array output voltage U of the photovoltaic power stationgDetermining the output voltage U of a DC/DC chopper circuitd0;
And 4, step 4: according to the frequency modulation ratio N of the inverter, the amplitude modulation ratio M of the inverter and the photovoltaic array output voltage U of the photovoltaic power stationgCalculating harmonic voltage U output by inverterxhl;
The frequency modulation ratio N according to the inverter, the amplitude modulation ratio M according to the inverter and the photovoltaic array output voltage U of the photovoltaic power stationgCalculating harmonic voltage U output by inverterxhlThe calculation formula of (a) is as follows:
wherein m is the number of harmonics,fcis a carrier frequency, fmFor modulating the wave frequency, MmIs the carrier amplitude, McIn order to modulate the amplitude of the wave,for the second harmonic initial phase, n is 2k +1,., ∞, k is 1,2., ∞, and ω is the fundamental frequency;
and 5: according to the output voltage U of the DC/DC chopper circuitd0And harmonic voltage U of inverter outputxhlCalculating the harmonic content percentage v of the photovoltaic power station;
the calculation formula of the harmonic content percentage v of the photovoltaic power station is as follows:
step 6: and (3) judging whether the harmonic content percentage v of the current photovoltaic power station is less than or equal to a threshold value of the harmonic content percentage, if so, the DC/DC-DC/AC harmonic control process of the current photovoltaic power station meets the requirement, otherwise, adjusting the corresponding trigger angle of each trigger moment of the DC/DC chopper circuit so as to determine the trigger time of the SPWM of the photovoltaic power station, and returning to the step 3.
2. The photovoltaic power plant DC/DC-DC/AC harmonic control method according to claim 1, characterized in that the relationship between voltage values at different trigger times of the DC/DC chopper circuit and corresponding trigger angles at the trigger times is established as follows:
first trigger time voltage u of DC/DC chopper circuit1Firing angle α corresponding to a first firing time1The relationship of (A) is as follows:
wherein u ist=Ug,α3For the third trigger time corresponding to the trigger angle, α5For the fifth firing moment corresponding to firing angle, α7For the seventh trigger time corresponds to the trigger angle, α9The ninth trigger moment corresponds to a trigger angle;
third trigger time voltage u of DC/DC chopper circuit3Firing angle α corresponding to third firing time3The relationship of (A) is as follows:
voltage u at fifth trigger time of DC/DC chopper circuit5Firing angle α corresponding to the fifth firing time5The relationship of (A) is as follows:
seventh trigger time voltage u of DC/DC chopper circuit7Firing angle α corresponding to the seventh firing time7The relationship of (A) is as follows:
ninth trigger time voltage u of DC/DC chopper circuit9Firing angle α corresponding to ninth firing time9The relationship of (A) is as follows:
3. the photovoltaic power plant DC/DC-DC/AC harmonic control method of claim 1, wherein the output voltage U is a function of photovoltaic power plant photovoltaic array output voltage UgDetermining the output voltage U of a DC/DC chopper circuitd0The calculation formula of (a) is as follows:
where n is 2k + 1., ∞, k is 1,2., ∞, and ω is the fundamental frequency.
4. The photovoltaic plant DC/DC-DC/AC harmonic control method of claim 1 in which the threshold harmonic content percentage is 10%.
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CN109167395B (en) * | 2018-11-22 | 2021-10-15 | 国网宁夏电力有限公司电力科学研究院 | Transient equivalent potential identification method of photovoltaic power generation system based on ADPSS |
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CN1784817A (en) * | 2003-05-07 | 2006-06-07 | 株式会社荏原电产 | Power supply including system interconnection inverter |
EP2562919A1 (en) * | 2010-11-17 | 2013-02-27 | TBEA Sunoasis Co., Ltd. | Grid-connected inverter and ac harmonic filtering method for inverter |
CN203747431U (en) * | 2013-10-15 | 2014-07-30 | 北京凯门控制工程研究所 | DC/AC converter for photovoltaic power-generation grid-connected system based on phase-shifting transformer |
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CN1784817A (en) * | 2003-05-07 | 2006-06-07 | 株式会社荏原电产 | Power supply including system interconnection inverter |
EP2562919A1 (en) * | 2010-11-17 | 2013-02-27 | TBEA Sunoasis Co., Ltd. | Grid-connected inverter and ac harmonic filtering method for inverter |
CN203747431U (en) * | 2013-10-15 | 2014-07-30 | 北京凯门控制工程研究所 | DC/AC converter for photovoltaic power-generation grid-connected system based on phase-shifting transformer |
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光伏发电PWM逆变器谐波抑制方法研究;任神河;《中国优秀硕士学位论文全文数据库(电子期刊)工程科技Ⅱ辑》;20140615(第6期);正文第1-64页 * |
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