CN111313427B - Photovoltaic power generation voltage control method and system based on impedance measurement - Google Patents

Photovoltaic power generation voltage control method and system based on impedance measurement Download PDF

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CN111313427B
CN111313427B CN202010175133.8A CN202010175133A CN111313427B CN 111313427 B CN111313427 B CN 111313427B CN 202010175133 A CN202010175133 A CN 202010175133A CN 111313427 B CN111313427 B CN 111313427B
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许炜
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Jiangsu Chenxin Hongda Power Technology Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • 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
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • 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
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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    • Y02E40/30—Reactive power compensation

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Abstract

A photovoltaic power generation voltage control method based on impedance measurement comprises the following steps: step 1, monitoring the power grid impedance ratio under the fundamental frequency of a power grid, and specifically comprising the following steps: step 2, controlling the photovoltaic power generation voltage according to the impedance ratio of the line power grid; the invention provides a photovoltaic power generation voltage control method and system based on impedance measurement for a photovoltaic power station, which can dynamically and accurately observe the impedance ratio of a power grid, and can dynamically control the active power and the reactive power injected into the power grid by a photovoltaic inverter, thereby improving the control effect of the photovoltaic inverter on the voltage of the power grid.

Description

Photovoltaic power generation voltage control method and system based on impedance measurement
Technical Field
The invention relates to a photovoltaic power generation voltage control method and system based on impedance measurement, and belongs to the technical field of photovoltaic power generation operation in the new energy power generation technology.
Background
As the grid-connected capacity of the distributed power generation device gradually increases, the distributed power generation device cannot inject active power into the power grid as a simple power supply, and the distributed power generation device should bear the burden of maintaining the stability of the power grid. However, the existing distributed power generation devices do not participate in the voltage control of the power grid, so that, taking photovoltaic power generation as an example, the sunlight is sufficient in the daytime, and the voltage of the power grid is increased under the condition of light power load; in contrast, there is no sun exposure at night, and in the case of heavy electrical loads, the grid voltage decreases. One solution is to control the output of the photovoltaic inverter according to the grid voltage. When the grid voltage deviates from the nominal value, the active power and the reactive power output by the photovoltaic inverter are regulated to control the grid voltage accordingly. Because the power grid voltage is influenced by the impedance ratio of the power grid, the impedance ratio of the power grid can be measured in advance and input into a control strategy. However, the grid impedance ratio is not fixed, and changes occur along with the switching-in and switching-out of loads and the change of the grid topology. Especially in a low-voltage power grid, the change range of the impedance ratio of the power grid can be very large, the monitoring is inaccurate, and the overvoltage of the power grid is easy to generate.
Disclosure of Invention
The invention aims to disclose a photovoltaic power generation voltage control method and system based on impedance measurement.
The technical scheme of the invention is as follows.
A photovoltaic power generation voltage control method based on impedance measurement comprises the following steps:
step 1, monitoring the power grid impedance ratio under the fundamental frequency of a power grid, and specifically comprising the following steps:
and 2, controlling the photovoltaic power generation voltage according to the impedance ratio of the line power grid.
Preferably, step 1 specifically comprises the following steps:
s101, controlling harmonic current to be injected into a power grid, wherein the amplitude of the harmonic current is B, the action time of the harmonic current is T, adding a control signal of which the amplitude is B and the action time of the harmonic current is T under the control of an original fundamental wave dq coordinate system, and injecting the harmonic current into the power grid is a formula (1):
Figure GDA0002462830210000021
in the formula id.refAnd iq.refIs a d-axis given signal and a q-axis given signal i after injection of harmonicsd.ref.50And iq.ref.50Is d-axis control signal and q-axis control signal of fundamental wave (50Hz), B is harmonic current amplitude, t is time variable;
s102, calculating harmonic voltage components v in the network-access voltage and the current by using Discrete Fourier Transform (DFT)g75And harmonic current component iL75；
S103, monitoring the power grid impedance ratio R/X under the fundamental frequency.
Preferably, step S102 specifically includes the following steps:
1021) measuring the actual three-phase voltage v of the grida，vb，vcThe actual voltage of the grid is denoted vg，vg＝[va,vb,vc]The actual current i of the gridLa，iLb，iLcIs represented by iL，iL＝[iLa，iLb，iLc]；
1022) Calculating the actual voltage v of the harmonic by using DFT formulag75And harmonic actual current iL75
Figure GDA0002462830210000022
In the formula, N is v sampled by harmonic current action time Tg(or i)L) Number of points, vg(n) and iLAnd (n) is the sampling data of each point.
Preferably, step S103 specifically includes:
1031) method for solving system impedance Z under original fundamental wave 50Hz by applying approximate formula (3)g(50Hz)；
Figure GDA0002462830210000031
R [ ], X [ ] are impedance coefficients;
1032) according to Zg(50Hz) and vg75And iL75Solves the impedance ratio R/X as formula (4):
Figure GDA0002462830210000032
where Re () and Im () represent the real and imaginary parts of the complex number, respectively.
Preferably, step 2 specifically comprises the following steps:
s201, defining the impedance ratio at the time t
Figure GDA0002462830210000033
Is formula (5):
Figure GDA0002462830210000034
s202, controlling the actual active power of the system according to alpha (t);
and S203, controlling the actual reactive power of the system according to alpha (t).
Preferably, step S202 specifically includes the following steps:
2021) active power p corresponding to maximum power point tracking point of system at t moment is collected0(t)；
2022) Based on the time point α (t), calculating the actual active power given p (t) corresponding to the system according to the formula (6):
Figure GDA0002462830210000035
in the formula, kpDroop control parameter, v, for active power0Setting a component of a rated control voltage corresponding to the d axis, v, for the systemdAnd (t) is the component of the actual voltage under the d-axis at time t.
Preferably, step S203 specifically includes the following steps:
2031) calculating system reactive current command deviation △ iq(t), formula (7):
Figure GDA0002462830210000041
in the formula, kqDroop control parameter, v, for reactive power0Setting a component of a rated control voltage corresponding to the d axis, v, for the systemd(t) is the component of the actual voltage under the d-axis at time t;
2032) △ iq(t) as a compensation quantity, adding the compensation quantity into the given of harmonic current injection power grid network, and obtaining a formula (8):
iq.ref＝iq.ref.50+Bsin(2π25t)+Δiq(t)
(8)。
a photovoltaic power generation voltage control system based on impedance measurement comprises a power grid impedance ratio observation trigger, a DFT calculation unit, a power grid impedance ratio observer, a harmonic current generator and a photovoltaic power generation voltage control unit, wherein the photovoltaic power generation voltage control unit comprises a reactive power controller, an active power controller and an active power communication unit;
the power grid impedance ratio observer, the DFT calculation unit, the harmonic current generator, the reactive power controller, the active power controller and the active power communication unit are sequentially connected; and the DFT calculation unit and the harmonic current generator are connected with a power grid impedance ratio observation trigger.
The power grid impedance ratio observation trigger triggers a harmonic current generator to generate harmonic current, the amplitude of the harmonic current is B, the action time of the harmonic current is T, the injection method is that a control signal with the amplitude of B, the frequency of 25Hz and the action time of the harmonic current is T is added under the control of an original fundamental wave dq coordinate system, and the injection of the harmonic current into the power grid is a formula (1):
Figure GDA0002462830210000042
in the formula id.refAnd iq.refIs a d-axis given signal and a q-axis given signal i after injection of harmonicsd.ref.50And iq.ref.50Is d-axis control signal and q-axis control signal of fundamental wave (50Hz), B is harmonic current amplitude, t is time variable;
the DFT calculating unit calculates harmonic voltage components v in the network access voltage and the currentg75And harmonic current component iL75(ii) a Calculating the harmonic actual voltage v using DFT equation 2(DFT equation)g75And harmonic actual current iL75；
Figure GDA0002462830210000051
In the formula (2), N is v of harmonic current action time T samplingg(or i)L) Number of points, vg(n) and iL(n) the sampled data for each point;
measuring actual three-phase voltage v of power grid by power grid impedance ratio observera，vb，vcThe actual voltage of the grid is denoted vg，vg＝[va,vb,vc]The actual current i of the gridLa，iLb，iLcIs represented by iL，iL＝[iLa，iLb，iLc]；
The impedance ratio observer of the power grid monitors the impedance ratio at the moment t
Figure GDA0002462830210000052
Is formula (5):
Figure GDA0002462830210000053
a power grid impedance ratio observer monitors a power grid impedance ratio R/X under fundamental frequency;
the photovoltaic power generation voltage control unit controls the photovoltaic power generation voltage according to the impedance ratio of the line power grid;
the power grid impedance ratio observer sends alpha (t) to an active power controller through an active power communication unit to control the actual active power of the system,
obtaining the active power p corresponding to the maximum power tracking point of the system at the moment t0(t)；
According to the alpha (t), the active power controller obtains the actual active power given p (t) corresponding to the system:
Figure GDA0002462830210000054
in the formula, kpDroop control parameter, v, for active power0Setting a component of a rated control voltage corresponding to the d axis, v, for the systemd(t) is the component of the actual voltage under the d-axis at time t;
and the reactive power controller receives alpha (t) and controls the actual reactive power of the system.
The observation and monitoring process of the power grid impedance ratio observer specifically comprises the following steps:
1031) method for solving system impedance Z under original fundamental wave 50Hz by applying approximate formula (3)g(50Hz)；
Figure GDA0002462830210000061
According to Zg(50Hz) and vg75And iL75Solves the impedance ratio R/X as formula (4):
Figure GDA0002462830210000062
where Re () and Im () represent the real and imaginary parts of the complex number, respectively.
The specific control process of the reactive power controller comprises the following steps:
2031) calculating system reactive current command deviation △ iq(t), formula (7):
Figure GDA0002462830210000063
in the formula, kqDroop control parameter, v, for reactive power0Setting a component of a rated control voltage corresponding to the d axis, v, for the systemd(t) is the component of the actual voltage under the d-axis at time t;
2032) △ iq(t) as a compensation quantity, added to the given of the current loop (harmonic current injection into the grid network), is formula (8):
iq.ref＝iq.ref.50+Bsin(2π25t)+Δiq(t)(8)。
the invention achieves the following beneficial effects:
(1) the invention provides a photovoltaic power generation voltage control method and system based on impedance measurement for a photovoltaic power station, which can dynamically and accurately observe the impedance ratio of a power grid, and can dynamically control the active power and the reactive power injected into the power grid by a photovoltaic inverter, thereby improving the control effect of the photovoltaic inverter on the voltage of the power grid; the invention monitors the system impedance in real time by triggering harmonic wave, calculates the compensation amount, adds the compensation amount into the given process of a current loop (harmonic current is injected into a power grid network), performs closed-loop control, and has accurate control;
(2) the photovoltaic power generation voltage control method and system based on impedance measurement can improve the voltage level of a power grid, so that a photovoltaic inverter can still transmit electric energy to the power grid under the condition of non-optimal power grid voltage.
Drawings
FIG. 1 is a flow chart of a photovoltaic power generation voltage control method based on impedance measurement according to the present invention;
FIG. 2 is a schematic circuit diagram of an exemplary test system;
FIG. 3 is a diagram showing the error between the simulation and the actual value of the impedance observation in the embodiment;
fig. 4 shows the voltage control effect of the proposed strategy in the example.
Detailed Description
The method of the present invention is further described in detail below with reference to the drawings and examples.
As shown in fig. 1, the technical solution of the present invention is:
a photovoltaic power generation voltage control method based on impedance measurement comprises the following steps:
step 1, monitoring the power grid impedance ratio under the fundamental frequency of a power grid, and specifically comprising the following steps:
s101, controlling 75Hz harmonic current to be injected into a power grid, wherein the amplitude of the harmonic current is B, the acting time of the harmonic current is T, and T is 40ms, the injection method is that a control signal with the amplitude of B, the frequency of 25Hz and the acting time of the harmonic current of 40ms is added under the control of an original fundamental wave (50Hz) dq coordinate system, and the injection of the harmonic current into the power grid is formula (1):
Figure GDA0002462830210000071
in the formula id.refAnd iq.refIs a d-axis given signal and a q-axis given signal i after injection of harmonicsd.ref.50And iq.ref.50Is d-axis control signal and q-axis control signal of fundamental wave (50Hz), B is harmonic current amplitude, t is time variable;
s102, calculating 75Hz harmonic voltage component v in the network voltage and current by using Discrete Fourier Transform (DFT)g75And harmonic current component iL75The method specifically comprises the following steps:
1021) measuring the actual three-phase voltage v of the grida，vb，vcThe actual voltage of the grid is denoted vg，vg＝[va,vb,vc]The actual current i of the gridLa，iLb，iLcIs represented by iL，iL＝[iLa，iLb，iLc]；
1022) Calculating the actual voltage of the harmonic by using DFT formulavg75And harmonic actual current iL75
Figure GDA0002462830210000081
Wherein N is v sampled at harmonic current action time of 40msg(or i)L) Number of points, vg(n) and iLAnd (n) is the sampling data of each point.
S103, monitoring the power grid impedance ratio R/X under the fundamental frequency, and specifically comprising the following steps:
1031) method for solving system impedance Z under original fundamental wave 50Hz by applying approximate formula (3)g(50Hz)；
Figure GDA0002462830210000082
R [ ], X [ ] are impedance coefficients;
1032) according to Zg(50Hz) and vg75And iL75Solves the impedance ratio R/X as formula (4):
Figure GDA0002462830210000083
where Re () and Im () represent the real and imaginary parts of the complex number, respectively.
Step 2, controlling the photovoltaic power generation voltage according to the impedance ratio of the line power grid;
s201, defining the impedance ratio at the time t
Figure GDA0002462830210000084
Is formula (5):
Figure GDA0002462830210000085
s202, controlling the actual active power of the system according to α (t), specifically including:
2021) active power p corresponding to maximum power point tracking point of system at t moment is collected0(t)；
2022) Based on the time point α (t), calculating the actual active power given p (t) corresponding to the system according to the formula (6):
Figure GDA0002462830210000091
in the formula, kpDroop control parameter, v, for active power0Setting a component of a rated control voltage corresponding to the d axis, v, for the systemd(t) is the component of the actual voltage under the d-axis at time t;
s203, controlling the actual reactive power of the system according to α (t), specifically including:
2031) calculating system reactive current command deviation △ iq(t), formula (7):
Figure GDA0002462830210000092
in the formula, kqDroop control parameter, v, for reactive power0Setting a component of a rated control voltage corresponding to the d axis, v, for the systemdAnd (t) is the component of the actual voltage under the d-axis at time t.
2032) △ iq(t) as a compensation quantity, adding the compensation quantity into the given of harmonic current injection power grid network, and obtaining a formula (8):
iq.ref＝iq.ref.50+Bsin(2π25t)+Δiq(t)(8)。
after the system of the embodiment acquires the impedance of the power grid, the photovoltaic power generation voltage control is implemented according to the flow of fig. 1. Based on the simulation system illustrated in fig. 2, experimental research is performed on the voltage control strategy of the photovoltaic inverter under different grid impedance conditions. Wherein the grid impedance ratio is observed online using the method described above. At each grid impedance ratio, two comparative experiments were performed, one without and one with a grid voltage control strategy.
A photovoltaic power generation voltage control system based on impedance measurement comprises a power grid impedance ratio observation trigger, a DFT calculation unit, a power grid impedance ratio observer, a harmonic current generator and a photovoltaic power generation voltage control unit, wherein the photovoltaic power generation voltage control unit comprises a reactive power controller, an active power controller and an active power communication unit;
the power grid impedance ratio observer, the DFT calculation unit, the harmonic current generator, the reactive power controller, the active power controller and the active power communication unit are sequentially connected; and the DFT calculation unit and the harmonic current generator are connected with a power grid impedance ratio observation trigger.
The power grid impedance ratio observation trigger triggers a harmonic current generator to generate 75Hz harmonic current, the amplitude of the harmonic current is B, the action time of the harmonic current is T, the T is 40ms, the injection method is that a control signal with the amplitude of B, the frequency of 25Hz and the action time of the harmonic current of 40ms is added under the control of an original fundamental wave (50Hz) dq coordinate system, and the injection of the harmonic current into the power grid is formula (1):
Figure GDA0002462830210000101
in the formula id.refAnd iq.refIs a d-axis given signal and a q-axis given signal i after injection of harmonicsd.ref.50And iq.ref.50Is d-axis control signal and q-axis control signal of fundamental wave (50Hz), B is harmonic current amplitude, t is time variable;
the DFT calculating unit calculates 75Hz harmonic voltage component v in the network access voltage and currentg75And harmonic current component iL75(ii) a Calculating the harmonic actual voltage v using DFT equation 2(DFT equation)g75And harmonic actual current iL75
Figure GDA0002462830210000102
Wherein N is v sampled at harmonic current action time of 40msg(or i)L) Number of points, vg(n) and iLAnd (n) is the sampling data of each point.
Measuring actual three-phase voltage v of power grid by power grid impedance ratio observera，vb，vcThe actual voltage of the grid is denoted vg，vg＝[va,vb,vc]The actual current i of the gridLa，iLb，iLcIs represented by iL，iL＝[iLa，iLb，iLc]；
The impedance ratio observer of the power grid monitors the impedance ratio at the moment t
Figure GDA0002462830210000103
Is formula (5):
Figure GDA0002462830210000104
the method comprises the following steps that a power grid impedance ratio observer monitors a power grid impedance ratio R/X under fundamental wave frequency, and the observation and monitoring process of the power grid impedance ratio observer specifically comprises the following steps:
1031) method for solving system impedance Z under original fundamental wave 50Hz by applying approximate formula (3)g(50Hz)；
Figure GDA0002462830210000105
Wherein, Vg(h) And IL(h) H is the harmonic order 75 as calculated by DFT.
The injected harmonic frequencies should be as close as possible to the fundamental frequency so that the approximation of (4) is valid. At the same time, the effect of the harmonics on the grid should also be as small as possible. In simulation and experiment, the photovoltaic inverter injects 75Hz harmonic current into a power grid to carry out online observation on the impedance ratio of the power grid.
According to Zg(50Hz) and vg75And iL75Solves the impedance ratio R/X as formula (4):
Figure GDA0002462830210000111
where Re () and Im () represent the real and imaginary parts of the complex number, respectively.
The photovoltaic power generation voltage control unit controls the photovoltaic power generation voltage according to the impedance ratio of the line power grid;
the power grid impedance ratio observer sends alpha (t) to an active power controller through an active power communication unit to control the actual active power of the system,
obtaining the active power p corresponding to the maximum power tracking point of the system at the moment t0(t)；
According to the alpha (t), the active power controller obtains the actual active power given p (t) corresponding to the system:
Figure GDA0002462830210000112
in the formula, kpDroop control parameter, v, for active power0Setting a component of a rated control voltage corresponding to the d axis, v, for the systemd(t) is the component of the actual voltage under the d-axis at time t;
the reactive power controller receives alpha (t), controls the actual reactive power of the system, and the specific control process of the reactive power controller comprises the following steps:
2031) calculating system reactive current command deviation △ iq(t), formula (7):
Figure GDA0002462830210000113
in the formula, kqDroop control parameter, v, for reactive power0Setting a component of a rated control voltage corresponding to the d axis, v, for the systemdAnd (t) is the component of the actual voltage under the d-axis at time t.
2032) △ iq(t) as a compensation quantity, added to the given of the current loop (harmonic current injection into the grid network), is formula (8):
iq.ref＝iq.ref.50+Bsin(2π25t)+Δiq(t)(8)。
in this embodiment, V required for calculating the grid impedance ratiog(h) And IL(h) The method is obtained by calculating DFT sampled values of the power grid voltage and the power grid current. The harmonic current injected into the grid should meet the following 2 point requirements. First, the THD cannot be increased significantly, thus injecting harmonic currentsThe time of (a) is to be as short as possible; secondly, it should be ensured that enough samples are received to complete the DFT to obtain an accurate impedance ratio result. Typically, the 75Hz harmonic current is injected for 40ms[9]. That is, the sampling points include 3 periods of harmonic voltage current sampling points and 2 periods of fundamental voltage current sampling points. 40ms is also the least common multiple of the fundamental and harmonic periods. Thus, the fundamental frequency of DFT is fswhere/N is 25Hz, where fsIn simulation and experiment, 3kHz is selected as the sampling frequency; n is the number of sampling points, 120 sampling points of the power grid voltage and the power grid current are obtained in 40ms, corresponding to the sampling frequency, and a large storage space cannot be required when the successive accumulation DFT algorithm is operated. The fundamental frequency of the DFT is 25Hz, then the 75Hz harmonic is the 3 rd harmonic in the DFT result.
In the DFT calculation result, the expression of 3 rd harmonic (75Hz) is (6). Wherein, N is 120, which is the number of sampling points; v (n) is sample data.
Figure GDA0002462830210000121
When the impedance ratio is larger than 1, the online observation result of the impedance ratio is very accurate, and the error relative to the actual impedance ratio is less than 5%. When the impedance ratio is less than 1, the online observation result of the impedance ratio is inaccurate, and the relative error increases significantly with the decrease of the impedance ratio. The resistance observations and reactance observations were further analyzed separately as shown in fig. 4. The abscissa is the actual impedance ratio of the power grid, the solid point of the ordinate is the relative error of the online observation result of the resistance of the power grid relative to the actual resistance of the power grid, and the hollow point of the ordinate is the relative error of the online observation result of the reactance of the power grid relative to the actual reactance of the power grid.
In an experiment without using a power grid voltage control strategy, the energy collection converter operates at a maximum power tracking point, and the photovoltaic inverter injects active power into a power grid as much as possible. In experiments using grid voltage control strategies, the energy harvesting converters were operated at the power points required for grid voltage control using the control strategies studied herein.
As shown in fig. 3 and 4, when the grid voltage control strategy is not used, the photovoltaic inverter injects active power into the grid as much as possible, and when the impedance ratio of the grid is increased, it can be seen that the overvoltage phenomenon is relieved. When the grid impedance ratio is greater than 4, the grid voltage can also be below 110% of the nominal value. As the impedance ratio increases, the voltage drop across Rg2 and Xg2 in the figure increases, and therefore the overvoltage of the grid voltage Vg with respect to the nominal value is mitigated. At the same time, the difference between Vg and the nominal value is used to generate an active power command value and a reactive power command value for the photovoltaic inverter, and accordingly, the active power controller requires a smaller direct current and the reactive power controller requires a larger reactive current. The overvoltage control mainly passes through active power, so that the control effect of the grid voltage control strategy is not more effective in the case of large grid impedance than in the case of small grid impedance. However, if the improvement effect of the grid voltage control strategy on the overvoltage is evaluated from a relative perspective, the following results can also be obtained. When the impedance ratio of the power grid is more than 1.5, the overvoltage phenomenon of the power grid is improved by about 20 percent; when the grid impedance ratio is less than 1.5, the grid overvoltage phenomenon improves by about 40%. The power grid voltage control strategy obviously improves the power grid overvoltage phenomenon.
In the description provided herein, numerous specific details are set forth. It is understood, however, that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.
Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. However, the disclosed method should not be interpreted as reflecting an intention that: that the invention as claimed requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.
Those skilled in the art will appreciate that the modules or units or groups of devices in the examples disclosed herein may be arranged in a device as described in this embodiment, or alternatively may be located in one or more devices different from the devices in this example. The modules in the foregoing examples may be combined into one module or may be further divided into multiple sub-modules.
Those skilled in the art will appreciate that the modules in the device in an embodiment may be adaptively changed and disposed in one or more devices different from the embodiment. Modules or units or groups in embodiments may be combined into one module or unit or group and may furthermore be divided into sub-modules or sub-units or sub-groups. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and all of the processes or elements of any method or apparatus so disclosed, may be combined in any combination, except combinations where at least some of such features and/or processes or elements are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise.
Furthermore, those skilled in the art will appreciate that while some embodiments described herein include some features included in other embodiments, rather than other features, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the following claims, any of the claimed embodiments may be used in any combination.
Furthermore, some of the described embodiments are described herein as a method or combination of method elements that can be performed by a processor of a computer system or by other means of performing the described functions. A processor having the necessary instructions for carrying out the method or method elements thus forms a means for carrying out the method or method elements. Further, the elements of the apparatus embodiments described herein are examples of the following apparatus: the apparatus is used to implement the functions performed by the elements for the purpose of carrying out the invention.
The various techniques described herein may be implemented in connection with hardware or software or, alternatively, with a combination of both. Thus, the methods and apparatus of the present invention, or certain aspects or portions thereof, may take the form of program code (i.e., instructions) embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, or any other machine-readable storage medium, wherein, when the program is loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention.
In the case of program code execution on programmable computers, the computing device will generally include a processor, a storage medium readable by the processor (including volatile and non-volatile memory and/or storage elements), at least one input device, and at least one output device. Wherein the memory is configured to store program code; the processor is configured to execute the method for evaluating photovoltaic absorption capacity of the present invention according to instructions in the program code stored in the memory.
By way of example, and not limitation, computer readable media may comprise computer storage media and communication media. Computer-readable media includes both computer storage media and communication media. Computer storage media store information such as computer readable instructions, data structures, program modules or other data. Communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. Combinations of any of the above are also included within the scope of computer readable media.
As used herein, unless otherwise specified the use of the ordinal adjectives "first", "second", "third", etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this description, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as described herein. Furthermore, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter. Accordingly, many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the appended claims. The present invention has been disclosed in an illustrative rather than a restrictive sense, and the scope of the present invention is defined by the appended claims.

Claims (8)

1. A photovoltaic power generation voltage control method based on impedance measurement is characterized by comprising the following steps:
step 1, monitoring the power grid impedance ratio under the fundamental frequency of a power grid, and specifically comprising the following steps:
step 2, controlling the photovoltaic power generation voltage according to the impedance ratio of the line power grid;
the step 2 specifically comprises the following steps:
s201, defining the impedance ratio at the time t
Figure FDA0002616732760000011
Is formula (5):
Figure FDA0002616732760000012
s202, controlling the actual active power of the system according to alpha (t);
and S203, controlling the actual reactive power of the system according to alpha (t).
Step S202 specifically includes the following steps:
2021) active power p corresponding to maximum power point tracking point of system at t moment is collected0(t)；
2022) Based on the time point α (t), calculating the actual active power given p (t) corresponding to the system according to the formula (6):
Figure FDA0002616732760000013
in the formula, kpDroop control parameter, v, for active power0Setting a component of a rated control voltage corresponding to the d axis, v, for the systemdAnd (t) is the component of the actual voltage under the d-axis at time t.
2. The photovoltaic power generation voltage control method based on impedance measurement according to claim 1,
the step 1 specifically comprises the following steps:
s101, controlling harmonic current to be injected into a power grid, wherein the amplitude of the harmonic current is B, the action time of the harmonic current is T, adding a control signal of which the amplitude is B and the action time of the harmonic current is T under the control of an original fundamental wave dq coordinate system, and injecting the harmonic current into the power grid is a formula (1):
Figure FDA0002616732760000021
in the formula id.refAnd iq.refIs a d-axis given signal and a q-axis given signal i after injection of harmonicsd.ref.50And iq.ref.50D-axis control signals and q-axis control signals of fundamental waves, B is a harmonic current amplitude, and t is a time variable;
s102, calculating harmonic voltage components v in network access voltage and current by using discrete Fourier analysisg75And harmonic current component iL75；
S103, monitoring the power grid impedance ratio R/X under the fundamental frequency.
3. The photovoltaic power generation voltage control method based on impedance measurement according to claim 1,
step S102 specifically includes the following steps:
1021) measuring the actual three-phase voltage v of the grida，vb，vcThe actual voltage of the grid is denoted vg，vg＝[va,vb,vc]The actual current i of the gridLa，iLb，iLcIs represented by iL，iL＝[iLa，iLb，iLc]；
1022) Calculating the actual voltage v of the harmonic by using DFT formulag75And harmonic actual current iL75
Figure FDA0002616732760000022
In the formula, N is the number of sampling points of the harmonic current action time T, vg(n) and iLAnd (n) is the sampling data of each point.
4. The photovoltaic power generation voltage control method based on impedance measurement according to claim 1,
step S103 specifically includes:
1031) method for solving system impedance Z under original fundamental wave by using approximate formulag(50Hz)；
Figure FDA0002616732760000023
R [ ], X [ ] are impedance coefficients;
1032) according to Zg(50Hz) and vg75And iL75Solves the impedance ratio R/X as formula (4):
Figure FDA0002616732760000031
where Re () and Im () represent the real and imaginary parts of the complex number, respectively.
5. The photovoltaic power generation voltage control method based on impedance measurement according to claim 1,
step S203 specifically includes the following steps:
2031) calculating system reactive current command deviation △ iq(t), formula (7):
Figure FDA0002616732760000032
in the formula, kqDroop control parameter, v, for reactive power0Setting a component of a rated control voltage corresponding to the d axis, v, for the systemd(t) is the component of the actual voltage under the d-axis at time t;
2032) △ iq(t) as a compensation quantity, adding the compensation quantity into the given of harmonic current injection power grid network, and obtaining a formula (8):
iq.ref＝iq.ref.50+B sin(2π25t)+Δiq(t) (8)。
6. a photovoltaic power generation voltage control system based on impedance measurement is characterized in that,
the photovoltaic power generation voltage control unit comprises a reactive power controller, an active power controller and an active power communication unit;
the power grid impedance ratio observer, the DFT calculation unit, the harmonic current generator, the reactive power controller, the active power controller and the active power communication unit are sequentially connected; and the DFT calculation unit and the harmonic current generator are connected with a power grid impedance ratio observation trigger.
7. Photovoltaic power generation voltage control system based on impedance measurement according to claim 6, characterized in that
The power grid impedance ratio observation trigger triggers a harmonic current generator to generate harmonic current, the amplitude of the harmonic current is B, the action time of the harmonic current is T, the injection method is that a control signal with the amplitude of B, the frequency of 25Hz and the action time of the harmonic current is T is added under the control of an original fundamental wave dq coordinate system, and the injection of the harmonic current into the power grid is a formula (1):
Figure FDA0002616732760000041
in the formula id.refAnd iq.refIs a d-axis given signal and a q-axis given signal i after injection of harmonicsd.ref.50And iq.ref.50Is d-axis control signal and q-axis control signal of fundamental wave (50Hz), B is harmonic current amplitude, t is time variable;
the DFT calculating unit calculates harmonic voltage components v in the network access voltage and the currentg75And harmonic current component iL75(ii) a Calculating the harmonic actual voltage v using DFT equation 2g75And harmonic actual current iL75；
Figure FDA0002616732760000042
In the formula (2), N is the number of sampling points of the harmonic current action time T, vg(n) and iL(n) the sampled data for each point;
measuring actual three-phase voltage v of power grid by power grid impedance ratio observera，vb，vcThe actual voltage of the grid is denoted vg，vg＝[va,vb,vc]The actual current i of the gridLa，iLb，iLcIs represented by iL，iL＝[iLa，iLb，iLc]；
The impedance ratio observer of the power grid monitors the impedance ratio at the moment t
Figure FDA0002616732760000043
Is formula (5):
Figure FDA0002616732760000044
a power grid impedance ratio observer monitors a power grid impedance ratio R/X under fundamental frequency;
the photovoltaic power generation voltage control unit controls the photovoltaic power generation voltage according to the impedance ratio of the line power grid;
the power grid impedance ratio observer sends alpha (t) to an active power controller through an active power communication unit to control the actual active power of the system,
obtaining the active power p corresponding to the maximum power tracking point of the system at the moment t0(t)；
According to the alpha (t), the active power controller obtains the actual active power given p (t) corresponding to the system:
Figure FDA0002616732760000051
in the formula, kpDroop control parameter, v, for active power0Setting a component of a rated control voltage corresponding to the d axis, v, for the systemd(t) is the component of the actual voltage under the d-axis at time t;
and the reactive power controller receives alpha (t) and controls the actual reactive power of the system.
8. Photovoltaic power generation voltage control system based on impedance measurement according to claim 6, characterized in that
The observation and monitoring process of the power grid impedance ratio observer specifically comprises the following steps:
1031) method for solving system impedance Z under original fundamental wave 50Hz by applying approximate formula (3)g(50Hz)；
Figure FDA0002616732760000052
According to Zg(50Hz) and vg75And iL75Solves the impedance ratio R/X as formula (4):
Figure FDA0002616732760000053
wherein Re () and Im () represent the real and imaginary parts of the complex number, respectively;
the specific control process of the reactive power controller comprises the following steps:
2031) calculating system reactive current command deviation △ iq(t), formula (7):
Figure FDA0002616732760000054
in the formula, kqDroop control parameter, v, for reactive power0Setting a component of a rated control voltage corresponding to the d axis, v, for the systemd(t) is the component of the actual voltage under the d-axis at time t;
2032) adding Δ iq (t) as a compensation quantity into the given process of injecting harmonic current into the power grid network, and obtaining a formula (8):
iq.ref＝iq.ref.50+B sin(2π25t)+Δiq(t) (8)。
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