CN110263481B - Distributed photovoltaic transient characteristic test method - Google Patents
Distributed photovoltaic transient characteristic test method Download PDFInfo
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Abstract
The invention provides a distributed photovoltaic transient characteristic test method, which comprises the following steps: s1: constructing a digital simulation model of the photovoltaic power supply based on the power system simulation system; s2: connecting the digital simulation model with the photovoltaic controller to form a digital physical hybrid simulation model, and carrying out fault simulation on the photovoltaic power supply according to the digital physical hybrid simulation model; s3: and inputting the fault simulation result into a photovoltaic transient current equation set to obtain a full-current expression of light Fu Zantai corresponding to the photovoltaic power supply so as to represent the photovoltaic transient characteristic of the photovoltaic power supply. Compared with the traditional method which simply relies on digital simulation, the method can obtain the transient fault characteristic of the photovoltaic power supply more accurately, and can be effectively applied to relay protection setting calculation of the distribution network containing the distributed photovoltaic power supply.
Description
Technical Field
The invention relates to the technical field of power systems, in particular to a distributed photovoltaic transient characteristic test method.
Background
In recent years, along with development and utilization of clean energy advocated by China, a photovoltaic power supply is used as an emerging renewable clean energy, the proportion of the photovoltaic power supply in a power grid is higher and higher, and according to statistics of the national energy agency, the solar power generation grid-connected amount of China reaches 130.25GW by 2017, and is increased by 68.7% in the same way. Particularly in a power distribution network, photovoltaic power sources are connected into a power grid in a distributed mode in a large quantity, and the influence on relay protection of a power system caused by the photovoltaic power sources is paid attention to.
The fixed value calculation of the power grid relay protection is based on the short-circuit current of the system flowing protection when the fault occurs. The grid connection points of the photovoltaic power supply access power distribution network are usually close to the load area, namely the line end, so that the transmission form and the topological structure of the original system power distribution network are changed, and the power distribution network is powered by the original single-ended power supply and is changed into multi-terminal power supply. Therefore, the photovoltaic power supply is connected to bring adaptability to the original relay protection setting principle and method based on the single-ended power supply of the power grid.
Meanwhile, unlike the conventional synchronous generator power supply, photovoltaic power generation is used as an inversion type power supply to realize grid-connected output of power supply power through an inverter. When the power grid fails, the transient characteristics of the inverter are related to the control mode and parameters of the inverter, and the capacity of providing short-circuit current to the power grid is limited by the current capacity of the power electronic switching tube. Therefore, in the event of a grid fault, the calculation of the short-circuit current provided by the photovoltaic power supply cannot be solved according to conventional algorithms suitable for synchronous power supplies. This requires finding a more efficient way to calculate the short circuit current of the photovoltaic power supply, and at the same time, testing the transient characteristics of different photovoltaic power supplies by means of a test platform.
Disclosure of Invention
The present invention aims to solve at least one of the above technical problems.
Therefore, the invention aims to provide a distributed photovoltaic transient characteristic test method, which is based on RTDS hybrid simulation, can obtain the transient fault characteristic of a photovoltaic power supply more accurately compared with the traditional method of purely digital simulation, and can be effectively applied to relay protection setting calculation of a power distribution network containing the distributed photovoltaic power supply.
In order to achieve the above objective, an embodiment of the present invention provides a method for testing transient characteristics of distributed photovoltaic, including the following steps: s1: constructing a digital simulation model of the photovoltaic power supply based on the power system simulation system; s2: connecting the digital simulation model with a photovoltaic controller to form a digital physical hybrid simulation model, and carrying out fault simulation on the photovoltaic power supply according to the digital physical hybrid simulation model; s3: and inputting a fault simulation result into a photovoltaic transient current equation set to obtain a light Fu Zantai full current expression corresponding to the photovoltaic power supply so as to represent the photovoltaic transient characteristic of the photovoltaic power supply.
In addition, the distributed photovoltaic transient characteristic test method according to the above embodiment of the present invention may further have the following additional technical features:
in some examples, the S1 further comprises: the step S1, further comprises: s11: creating an engineering in a human-computer interface of the power system simulation system; s12: adding a hierarchical structure component and a special sub-model of power electronic equipment into the engineering; s13: building a photovoltaic array in the hierarchical structure component; s14: constructing a converter model in the special sub-model of the power electronic equipment; s15: an interface transformer is built, wherein the interface transformer is connected with a converter model through a first circuit breaker, and the interface transformer is connected with a power grid through a second circuit breaker so as to build a distributed photovoltaic grid-connected power generation model; s16: and constructing the input output quantity of the distributed photovoltaic grid-connected power generation model.
In some examples, the converter model includes: the device comprises an unloading circuit, a precharge circuit, a direct current bus, a 6-pulse commutation bridge and a filter.
In some examples, the output of the distributed photovoltaic grid-connected power generation model includes an analog output and a switching output; each analog output quantity is output to the power amplification unit through the GTIO board of the power amplification unit, each analog output quantity output by the power amplification unit is input as an analog quantity of the tested photovoltaic grid-connected controller, and each switch output quantity is output through the GTIO board of the power amplification unit and is input as a digital quantity of the unipolar photovoltaic grid-connected controller; the analog output comprises: three-phase voltage at the outlet of the converter, three-phase current at the outlet of the converter, direct-current bus current and direct-current bus voltage; the switching output quantity comprises a state signal of the second circuit breaker and a state signal of the first circuit breaker; the input quantity of the distributed photovoltaic grid-connected power generation model comprises digital input quantity, wherein the digital input quantity comprises trigger pulses of 6 bridge arms at the grid side of the converter, trigger pulses of an unloading circuit, control commands of a second circuit breaker, control commands of a first circuit breaker and trigger pulses of a pre-charging loop.
In some examples, the S2 further comprises: s21: connecting the distributed photovoltaic grid-connected power generation model with a tested photovoltaic grid-connected controller; s22: the tested photovoltaic grid-connected controller obtains fault sampling current of the distributed photovoltaic grid-connected power generation model to form a matrix
In some examples, the S21 further comprises: the three-phase voltage at the outlet of the converter and the three-phase current at the outlet of the converter are connected with a grid-connected control function module of the tested photovoltaic grid-connected controller; the direct current bus current is connected with a converter control function module of the tested photovoltaic grid-connected controller, and the direct current bus voltage is connected with an MPPT module of the tested photovoltaic grid-connected controller; the state signal of the second circuit breaker and the state signal of the first circuit breaker are respectively connected with a grid-connected control function module of the tested photovoltaic grid-connected controller; the grid-connected control function module of the tested photovoltaic grid-connected controller transmits a control command of a second circuit breaker to the second circuit breaker; the grid-connected control function module of the tested photovoltaic grid-connected controller transmits a control command of a first circuit breaker to the first circuit breaker; the grid-connected control function module of the tested photovoltaic grid-connected controller transmits trigger pulses of a pre-charging loop to the pre-charging loop; the method comprises the steps that a converter protection module of a tested photovoltaic grid-connected controller transmits trigger pulses of an unloading circuit to the unloading circuit; and the converter control function module of the tested photovoltaic grid-connected controller transmits trigger pulses of the 6 bridge arms at the converter grid side to the 6 bridge arms at the converter grid side.
In some examples, the S3 further comprises: s31: constructing the photovoltaic transient current equation set; s32: converting the photovoltaic transient current equation set to obtain a variable to be solved, and calculating the value of the variable to be solved; s33: substituting the calculated value of the variable to be solved into the photovoltaic transient current equation set to obtain a light Fu Zantai full current expression.
In some examples, the photovoltaic transient current equation set is:
i fg ＝i g +Δi g (1)；
wherein i is g For a normal operating current before a fault,
r is the initial phase angle of current g Is the equivalent resistance of the photovoltaic grid-connected loop, L g The equivalent inductance of the photovoltaic grid-connected loop;
ΔI fgmax the maximum value of fault current generated in the photovoltaic access loop for the grid fault voltage is calculated by the following formula:
wherein, the liquid crystal display device comprises a liquid crystal display device,
is the per unit value of the loop impedance.
In some examples, in the S32, a conversion formula for converting the photovoltaic transient current equation set is:
[ΔI g ]＝[A][X] (4)；
wherein matrix [ X ]]Comprises two variables to be solved, x respectively 1 ＝ΔI fgmax And (3) with
[A]Is a corresponding coefficient matrix;
the calculation formula for calculating the value of the variable to be solved is as follows:
[X]＝[A] + [ΔI g ] (5)；
[A] + ＝{[A] T ·[A]} -1 ·[A] T (6)。
in some examples, the light Fu Zantai full current expression is:
wherein i is fg Is the light Fu Zantai full current expression.
According to the distributed photovoltaic transient characteristic test method provided by the embodiment of the invention, the digital simulation model of the photovoltaic power supply is built on the power system simulation system, and then the digital simulation model is connected with the tested photovoltaic controller through the external hardware interface to form a closed-loop test circuit, so that transient characteristic test and analysis are carried out on different types of photovoltaic power supplies. The method is mainly based on circuit parameters of the photovoltaic power supply, a mixed simulation test system consistent with physical characteristics of an actual photovoltaic power supply system is built based on a mathematical model of the photovoltaic power supply, so that transient characteristics of different photovoltaic power supplies are analyzed, and data support is provided for short circuit calculation of the photovoltaic power supply and relay protection setting of a photovoltaic power distribution network. Compared with the traditional method which simply relies on digital simulation, the method can obtain the transient fault characteristic of the photovoltaic power supply more accurately, and can be effectively applied to relay protection setting calculation of the distribution network containing the distributed photovoltaic power supply.
Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.
Drawings
The foregoing and/or additional aspects and advantages of the invention will become apparent and may be better understood from the following description of embodiments taken in conjunction with the accompanying drawings in which:
FIG. 1 is a flow chart of a distributed photovoltaic transient characteristic test method according to one embodiment of the present invention;
FIG. 2 is a schematic diagram of a simulation model of a photovoltaic array according to one embodiment of the present invention;
FIG. 3 is a schematic diagram of a simulation model of an inverter according to one embodiment of the invention;
FIG. 4 is a schematic diagram of a distributed photovoltaic grid-tie generation model according to one specific embodiment of the present invention;
FIG. 5 is a schematic diagram of a logical connection of a distributed photovoltaic grid-tie generation model to a photovoltaic grid-tie controller under test, according to one embodiment of the present invention;
FIG. 6 is a schematic diagram of electrical quantity connections of a distributed photovoltaic grid-tie generation model to a photovoltaic grid-tie controller under test, according to one specific embodiment of the present invention;
fig. 7 is a schematic diagram of the main electrical transient of a photovoltaic power supply according to one embodiment of the present invention.
Detailed Description
Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative only and are not to be construed as limiting the invention.
In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
The following describes a distributed photovoltaic transient characteristic test method according to an embodiment of the present invention with reference to the accompanying drawings.
Fig. 1 is a flow chart of a distributed photovoltaic transient characteristic test method according to one embodiment of the present invention. As shown in fig. 1, the method for testing transient characteristics of distributed photovoltaic comprises the following steps:
step S1: a digital simulation model of the photovoltaic power source is constructed based on a power system simulation system (Real Time Digital Simulator, RTDS). Specifically, a software model of a photovoltaic power supply primary system is built by using an electric power system simulation system RTDS, and a control hardware interface of the photovoltaic power supply is set.
In one embodiment of the present invention, step S1 further comprises:
step S11: an engineering (circle) is newly built in a human-machine interface (Draft) of a power system simulation system (RTDS).
Step S12: a hierarchy component (HIERARCHY COMPONENT) and a power electronics specific sub-model (vsc _BRIDGE_BOX) are added to the project (circle).
Step S13: a photovoltaic array is built in a hierarchical assembly (HIERARCHY COMPONENT).
The specific structure of the photovoltaic array is shown in fig. 2, which comprises pvv2.Def elements and buscon 1 elements; the pvv2.Def element has two external inputs and two outputs. Two external inputs are determined values, namely INSTRATION and TEMPERATURE, and the input values are directly given by two slide elements respectively, wherein the INSTRATION has an initial value of 1000, a maximum value of 2000, a minimum value of 0 and a unit of W/M2; the initial value of TEMPERATURE is set to 25, the maximum value is set to 80, the minimum value is set to-40, and the unit is set to Degree.
The two outputs are respectively connected with a bus identification element (BUSCONN 1) through a WIRE connection line; p and N, respectively, are connected to the buscon N1 element with a "WIRE" connection, the parameters "Name", "numc", "grafc" of which are set to "CBUS1", "2", "NONE", respectively.
Step S14: constructing a converter model in a power electronic equipment special sub-model vsc _bridge_box;
the converter model is connected with the photovoltaic array model data through vsc _ifctli1 elements, and element internal parameters of the converter model, namely, "Name", "prc12", "Lnm1", "numc", "dtyp", "Lgrd", "Rgrd", "Laer" and "rae", are respectively set as "PVC1", "CBUS1", "2", "Local", "0.0011", "0.0", "0.001", "0.0".
Specifically, as shown in connection with fig. 3, the converter model includes: the device comprises an unloading circuit, a precharge circuit, a direct current bus, a 6-pulse commutation bridge and a filter.
The unloading circuit comprises a vsc _VALVE1 element and a vsc _RES1 element which are connected in series, wherein parameters "vtype", "vswt", "iswt", "dswt", "bfreq", "prllr" of the vsc _VALVE1 element are respectively set to be "2", "0.5", "0.7", "50.0", "1.0". The parameter "R" of sc_res1 is set to "0.4".
The precharge circuit includes an embedded voltage source element (vsc _brc3) and a relay element (vsc _valv1), and is disposed in parallel with the unload circuit. The parameters "bty", "nmbr", "R", "L" of the embedded voltage source element (vsc _brc3) are set to "RL", "1", "0.1", "0.001", respectively. Parameters "vtype", "vswt", "iswt", "dswt", "bfreq", "prllr", "holdi" of the relay element (vsc _vale1) are set as "break", "2", "0.5", "0.7", "50.0", "1.0", "100", respectively.
The DC bus comprises an embedded branch element (vsc _BRC3) connected in parallel with the unloading circuit. Parameters "bty", "nmbr", "CMF" of the embedded branch element (vsc _BRC3) are respectively set as "C", "1", "25000", wherein the CMF is a capacitance value of the bus capacitor, preset as 25000MicroF, and the value can be modified according to different actual projects.
The 6-pulse commutation bridge comprises a three-phase six-pulse commutation bridge element (vsc _ph3 lev2) consisting of 6 insulated gate bipolar transistor elements. The parameters "nmlg1", "valvn", "sepr", "vswt", "dswt", "bfreq", "prllr" of VSC _ph3lev2 are set to "3", "VSC", "3", "2", "4", "0.7", "50", "1.0", respectively.
The filter comprises an embedded branching element (vsc _brc3) connected in series with one vsc _brc3 element at each phase output of the 6-pulse commutation bridge, the parameters "bty", "vsrc", "nmbr", "R", "L" of the current vsc _brc3 element being set to "RL", "No", "3", "0.001", "280e-6", respectively; the series connection is then connected to ground via a further vsc _brc3 element, the parameters "bty", "vsrc", "nmbr", "R", "C" of which are respectively designated "RC", "No", "3", "0.01", "200".
Step S15: and constructing an interface transformer, wherein the interface transformer is connected with the converter model through a first breaker BRK2, and the interface transformer is connected with a power grid through a second breaker BRK1 so as to construct a distributed photovoltaic grid-connected power generation model. For example, as shown in fig. 4, the interface transformer includes 3 single-phase transformer interface elements (vsc _ifctrf1), and the parameters "vtpri", "vtsec", "TMVA", "freqb", "trpos", "txpos" are set to "35", "0.2194", "0.83333", "50.0", "0.02743", "0.06", respectively.
Step S16: and constructing an input output quantity of the distributed photovoltaic grid-connected power generation model.
The output quantity of the distributed photovoltaic grid-connected power generation model comprises an analog output quantity and a switching output quantity.
Each analog output quantity is output to the power amplification unit through the GTIO board of the analog output unit, each analog output quantity output by the power amplification unit is input as an analog quantity of the tested photovoltaic grid-connected controller, and each switch output quantity is output through the GTIO board of the analog output unit and is input as a digital quantity of the unipolar photovoltaic grid-connected controller.
The analog output includes: the three-phase voltage VSA/B/C at the outlet of the converter (RTDS output transformation ratio is 0.69 kV/5V), the three-phase current CRTA/B/C at the outlet of the converter (RTDS output transformation ratio is 2.5 kA/5V), the direct current bus current IPV (RTDS output transformation ratio is 2 kV/5V) and the direct current bus voltage PVCAP (RTDS output transformation ratio is 3 kV/5V).
The switching output includes a status signal B1ST of the second circuit breaker BRK1 and a status signal B2ST of the first circuit breaker BRK2. And outputting the output quantity of each switch through a GTIO board of the switch as the digital quantity input of the unipolar photovoltaic grid-connected controller.
The input of the distributed photovoltaic grid-connected power generation model comprises a digital input. The digital input quantity comprises trigger pulses W1-6 of 6 bridge arms at the converter network side, trigger pulse CHOPCNTL of an unloading circuit VLV3, a control command B1CNTL of a second circuit breaker BRK1, a control command B2CNTL of a first circuit breaker BRK2 and trigger pulse V5CNTL of a pre-charging circuit VLV5.
Step S2: and connecting the digital simulation model with the photovoltaic controller to form a digital physical hybrid simulation model, and carrying out fault simulation on the photovoltaic power supply according to the digital physical hybrid simulation model. Specifically, the digital simulation model and the photovoltaic controller can be physically connected through a preset hardware interface, and fault simulation is performed.
In one embodiment of the present invention, step S2 further comprises:
step S21: and connecting the distributed photovoltaic grid-connected power generation model with the tested photovoltaic grid-connected controller.
Specifically, as shown in fig. 5 and 6, the three-phase voltage VSA/B/C at the outlet of the converter and the three-phase current CRTA/B/C at the outlet of the converter are connected with the grid-connected control function module of the tested photovoltaic grid-connected controller.
The direct current bus current IPV is connected with a converter control function module of the tested photovoltaic grid-connected controller, and the direct current bus voltage PVCAP is connected with an MPPT module of the tested photovoltaic grid-connected controller.
The state signal B1ST of the second circuit breaker BRK1 and the state signal B2ST of the first circuit breaker BRK2 are respectively connected with the grid-connected control function module of the tested photovoltaic grid-connected controller.
The grid-connected control function module of the tested photovoltaic grid-connected controller transmits a control command B1CNTL of the second circuit breaker BRK1 to the second circuit breaker BRK1; and the grid-connected control function module of the tested photovoltaic grid-connected controller transmits a control command B2CNTL of the first circuit breaker BRK2 to the first circuit breaker BRK2.
And the grid-connected control function module of the tested photovoltaic grid-connected controller pre-charges the trigger pulse V5CNTL of the loop VLV5 to the pre-charge loop VLV5 of the distributed photovoltaic grid-connected simulation model.
The converter protection module of the tested photovoltaic grid-connected controller transmits trigger pulse CHOPCNTL of the unloading circuit VLV3 to the unloading circuit VLV3 of the distributed photovoltaic grid-connected simulation model.
The converter control function module of the tested photovoltaic grid-connected controller transmits trigger pulses W1-6 of 6 bridge arms of the converter grid side to the 6 bridge arms of the converter grid side of the distributed photovoltaic grid-connected simulation model.
The electrical and switching values in a distributed photovoltaic grid-connected power generation model (namely a digital simulation model) are led out through an RTDS hardware loop, and the parameter names and the channel transformation ratios are respectively set as follows: the method comprises the steps of outputting an analog quantity inverter outlet three-phase voltage VSA/B/C (RTDS output transformation ratio is 0.69 kV/5V), an inverter outlet three-phase current CRTA/B/C (RTDS output transformation ratio is 2.5 kA/5V), a photovoltaic direct current bus current IPV (RTDS output transformation ratio is 2 kV/5V) and a photovoltaic direct current bus voltage PVCAP (RTDS output transformation ratio is 3 kV/5V) in a model to a power amplifying unit (model is PAV-120B, wherein voltage channel amplification factor is 1V/20V, current channel amplification factor is 1V/4A) through a GTIO board, and using each analog quantity output by the power amplifying unit for analog quantity input of a tested photovoltaic controller; the RTDS output switching value is state signals B1ST and B2ST of circuit breakers BRK1 and BRK2, the state signals are directly output by the RTDS through a GTIO circuit board of the RTDS, the RTDS is used as digital input of a unipolar photovoltaic controller, and the level range is +/-5V; the RTDS photovoltaic model reserves digital quantity input quantities which are respectively trigger pulses W1-6 of 6 bridge arms at the converter network side, trigger pulse CHOPCNTL of an unloading circuit VLV3, a control command B1CNTL of a circuit breaker BRK1, a control command B2CNTL of a circuit breaker BRK2 and trigger pulse V5CNTL of a precharge circuit VLV5, and the level ranges of the quantities are +/-5V.
Step S22: the tested photovoltaic grid-connected controller obtains fault sampling current of a distributed photovoltaic grid-connected power generation model to form a matrix
Further, the main electric quantity of the distributed photovoltaic grid-connected simulation model (i.e. the distributed photovoltaic grid-connected power generation model) can be obtained simultaneously, for example, as shown in fig. 7. Fig. 7 shows a transient waveform of the main electrical quantity of the photovoltaic power supply when a three-phase short-circuit fault occurs at the midpoint of the transmission LINE1 in the system shown in fig. 3.
Step S3: and inputting the fault simulation result into a photovoltaic transient current equation set to obtain a full-current expression of light Fu Zantai corresponding to the photovoltaic power supply so as to represent the photovoltaic transient characteristic of the photovoltaic power supply. Specifically, the simulation result in the step S2 is substituted into a photovoltaic transient current equation set, coefficients in the equation set are solved through a matrix, so that a transient full current expression of the photovoltaic power supply is obtained, and the photovoltaic transient characteristic of the photovoltaic power supply is represented through the transient full current expression.
In one embodiment of the present invention, step S3 further comprises:
step S31: and constructing a photovoltaic transient current equation set.
Specifically, the photovoltaic transient current equation set is:
i fg ＝i g +Δi g (1)；
wherein i is g For a normal operating current before a fault,
r is the initial phase angle of current g Is the equivalent resistance of the photovoltaic grid-connected loop, L g The equivalent inductance of the photovoltaic grid-connected loop;
ΔI fgmax the maximum value of fault current generated in the photovoltaic access loop for the grid fault voltage is calculated by the following formula:
wherein, the liquid crystal display device comprises a liquid crystal display device,
is the per unit value of the loop impedance.
Due to R g 、L g The method cannot be accurately obtained in actual engineering, and is obtained by solving an equation through amplitude sampling of transient current, so that step S32 is performed for solving.
Step S32: and (3) converting the photovoltaic transient current equation set in the step S31 to obtain a variable to be solved, and calculating the value of the variable to be solved. Specifically, the equation 2 in step S31 is converted to obtain the variable to be solved.
In step S32, a conversion formula for converting formula 2 in the photovoltaic transient current equation set is:
[ΔI g ]＝[A][X] (4)；
wherein matrix [ X ]]Comprising two variables to be solved for,respectively x 1 ＝ΔI fgmax And (3) with
[A]Is a corresponding coefficient matrix;
further, the calculation formula for calculating the value of the variable to be calculated is:
[X]＝[A] + [ΔI g ] (5)；
[A] + ＝{[A] T ·[A]} -1 ·[A] T (6)。
s33: substituting the calculated value of the to-be-solved variable into a photovoltaic transient current equation set to obtain a light Fu Zantai full-current expression. Specifically, the calculated variable to be calculated is substituted into a formula 1 in a photovoltaic transient current equation set, so that an estimated analysis expression of the photovoltaic transient current is obtained, namely a full current expression of light Fu Zantai is obtained, and the photovoltaic transient characteristic of the photovoltaic power supply is represented.
Specifically, the full current expression of light Fu Zantai is:
wherein i is fg Is a light Fu Zantai full current expression.
In summary, the distributed photovoltaic transient characteristic test method is based on the RTDS, and a digital physical hybrid simulation system is built with an actual photovoltaic controller by building a digital model on the actual photovoltaic power supply and presetting a hardware interface so as to test the transient characteristics of different photovoltaic power supplies; and finally, solving an analytic equation of the photovoltaic transient current through simulation experiment results and a general expression of the photovoltaic transient current, and effectively applying the analytic equation to relay protection setting calculation of the distributed photovoltaic power distribution network.
According to the distributed photovoltaic transient characteristic test method provided by the embodiment of the invention, the digital simulation model of the photovoltaic power supply is built on the power system simulation system, and then the digital simulation model is connected with the tested photovoltaic controller through the external hardware interface to form a closed-loop test circuit, so that transient characteristic test and analysis are carried out on different types of photovoltaic power supplies. The method is mainly based on circuit parameters of the photovoltaic power supply, a mixed simulation test system consistent with physical characteristics of an actual photovoltaic power supply system is built based on a mathematical model of the photovoltaic power supply, so that transient characteristics of different photovoltaic power supplies are analyzed, and data support is provided for short circuit calculation of the photovoltaic power supply and relay protection setting of a photovoltaic power distribution network. Compared with the traditional method which simply relies on digital simulation, the method can obtain the transient fault characteristic of the photovoltaic power supply more accurately, and can be effectively applied to relay protection setting calculation of the distribution network containing the distributed photovoltaic power supply.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiments or examples. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
While embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that: many changes, modifications, substitutions and variations may be made to the embodiments without departing from the spirit and principles of the invention, the scope of which is defined by the claims and their equivalents.
Claims (6)
1. The distributed photovoltaic transient characteristic testing method is characterized by comprising the following steps of:
s1: constructing a digital simulation model of the photovoltaic power supply based on the power system simulation system;
s2: connecting the digital simulation model with a photovoltaic controller to form a digital physical hybrid simulation model, and carrying out fault simulation on the photovoltaic power supply according to the digital physical hybrid simulation model;
s3: inputting a fault simulation result into a photovoltaic transient current equation set to obtain a light Fu Zantai full current expression corresponding to the photovoltaic power supply so as to represent the photovoltaic transient characteristic of the photovoltaic power supply; the step S3 further comprises:
s31: constructing the photovoltaic transient current equation set;
s32: converting the photovoltaic transient current equation set to obtain a variable to be solved, and calculating the value of the variable to be solved;
s33: substituting the calculated value of the variable to be solved into the photovoltaic transient current equation set to obtain a light Fu Zantai full current expression;
the photovoltaic transient current equation set is as follows:
i fg ＝i g +Δi g (1)；
wherein i is g For a normal operating current before a fault,
r is the initial phase angle of current g Is the equivalent resistance of the photovoltaic grid-connected loop, L g The equivalent inductance of the photovoltaic grid-connected loop;
ΔI fgmax the maximum value of fault current generated in the photovoltaic access loop for the grid fault voltage is calculated by the following formula:
wherein, the liquid crystal display device comprises a liquid crystal display device,
is the per unit value of the loop impedance;
in S32, a conversion formula for converting the photovoltaic transient current equation set is as follows:
[ΔI g ]＝[A][X] (4)；
wherein matrix [ X ]]Comprises two variables to be solved, x respectively 1 ＝ΔI fgmax And (3) with
[A]]Is a corresponding coefficient matrix;
the calculation formula for calculating the value of the variable to be solved is as follows:
[X]＝[A] + [ΔI g ] (5)；
[A] + ＝{[A] T ·[A]} -1 ·[A] T (6)；
the light Fu Zantai full current expression is:
wherein i is fg Is the light Fu Zantai full current expression.
2. The distributed photovoltaic transient characteristic test method according to claim 1, wherein S1 further comprises:
s11: creating an engineering in a human-computer interface of the power system simulation system;
s12: adding a hierarchical structure component and a special sub-model of power electronic equipment into the engineering;
s13: building a photovoltaic array in the hierarchical structure component;
s14: constructing a converter model in the special sub-model of the power electronic equipment;
s15: an interface transformer is built, wherein the interface transformer is connected with a converter model through a first circuit breaker, and the interface transformer is connected with a power grid through a second circuit breaker so as to build a distributed photovoltaic grid-connected power generation model;
s16: and constructing the input output quantity of the distributed photovoltaic grid-connected power generation model.
3. The distributed photovoltaic transient characteristic test method according to claim 2, wherein the converter model comprises: the device comprises an unloading circuit, a precharge circuit, a direct current bus, a 6-pulse commutation bridge and a filter.
4. The method for testing the transient characteristics of the distributed photovoltaic system according to claim 3, wherein the output of the distributed photovoltaic grid-connected power generation model comprises an analog output and a switching output;
each analog output quantity is output to the power amplification unit through the GTIO board of the power amplification unit, each analog output quantity output by the power amplification unit is input as an analog quantity of the tested photovoltaic grid-connected controller, and each switch output quantity is output through the GTIO board of the power amplification unit and is input as a digital quantity of the unipolar photovoltaic grid-connected controller;
the analog output comprises: three-phase voltage at the outlet of the converter, three-phase current at the outlet of the converter, direct-current bus current and direct-current bus voltage;
the switching output quantity comprises a state signal of the second circuit breaker and a state signal of the first circuit breaker;
the input quantity of the distributed photovoltaic grid-connected power generation model comprises digital input quantity, wherein the digital input quantity comprises trigger pulses of 6 bridge arms at the grid side of the converter, trigger pulses of an unloading circuit, control commands of a second circuit breaker, control commands of a first circuit breaker and trigger pulses of a pre-charging loop.
5. The distributed photovoltaic transient characteristic test method according to claim 4, wherein S2 further comprises:
s21: connecting the distributed photovoltaic grid-connected power generation model with a tested photovoltaic grid-connected controller;
s22: the tested photovoltaic grid-connected controller obtains fault sampling current of the distributed photovoltaic grid-connected power generation model to form a matrix
Wherein I is fg Current is sampled for the fault.
6. The method for testing the transient characteristics of distributed photovoltaic according to claim 5, wherein S21 further comprises:
the three-phase voltage at the outlet of the converter and the three-phase current at the outlet of the converter are connected with a grid-connected control function module of the tested photovoltaic grid-connected controller;
the direct current bus current is connected with a converter control function module of the tested photovoltaic grid-connected controller, and the direct current bus voltage is connected with an MPPT module of the tested photovoltaic grid-connected controller;
the state signal of the second circuit breaker and the state signal of the first circuit breaker are respectively connected with a grid-connected control function module of the tested photovoltaic grid-connected controller;
the grid-connected control function module of the tested photovoltaic grid-connected controller transmits a control command of a second circuit breaker to the second circuit breaker;
the grid-connected control function module of the tested photovoltaic grid-connected controller transmits a control command of a first circuit breaker to the first circuit breaker;
the grid-connected control function module of the tested photovoltaic grid-connected controller transmits trigger pulses of a pre-charging loop to the pre-charging loop;
the method comprises the steps that a converter protection module of a tested photovoltaic grid-connected controller transmits trigger pulses of an unloading circuit to the unloading circuit;
and the converter control function module of the tested photovoltaic grid-connected controller transmits trigger pulses of the 6 bridge arms at the converter grid side to the 6 bridge arms at the converter grid side.
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