CN112993984A - Large-disturbance polymerization method for distributed photovoltaic power station under condition of electrical connection - Google Patents

Abstract

The invention relates to the field of distributed photovoltaic dynamic aggregation, in particular to a large disturbance aggregation method of a distributed photovoltaic power station under the condition of electrical connection. According to the national standard of photovoltaic low voltage ride-through and the measured inverter ride-through characteristics, the invention establishes a pscad electromagnetic transient model of a single photovoltaic; according to the electrical position of the photovoltaic power station in the system and the voltage drop characteristics of each distributed photovoltaic power station when fault occurs Group photovoltaics; group photovoltaics and lines in the same group to obtain the final aggregation model: photovoltaics are aggregated according to capacity, and line impedances are aggregated according to the principle of constant power and voltage before and after equal values. It has the following advantages: aggregating multiple photovoltaic power plants into a small number of photovoltaic power plants greatly reduces the simulation time and system scale; circuit aggregation takes into account both voltage loss and power loss, greatly improving accuracy; the external characteristics of photovoltaic power plants before and after aggregation are different. It can provide a theoretical basis for subsequent protection schemes and control strategies.

Description

A large-disturbance aggregation method for distributed photovoltaic power stations with electrical connections

technical field

The invention relates to the field of distributed photovoltaic dynamic aggregation, in particular to a large disturbance aggregation method of a distributed photovoltaic power station under the condition of electrical connection.

Background technique

In recent years, clean energy such as solar energy is replacing traditional fossil energy and has been widely developed and utilized. Because of its environmental protection and renewable characteristics, it can effectively alleviate the pressure on resources and the environment. favored and valued. In the future, with the development of smart grids and the needs of environmental protection, as well as the improvement and maturity of photovoltaic power generation industry technology, the demand for large-scale access and application of photovoltaics will increase day by day.

However, the integration of photovoltaics will bring a series of problems, such as reducing the inertia of the power system, making the power system's ability to resist disturbances weakened. Therefore, it is necessary to analyze and study the stability of photovoltaics after connecting to the power system. Existing simulation platforms have limited processing capabilities for scenarios where a large number of distributed photovoltaics are connected. Specifically, when photovoltaic modeling is performed, the simulation time of power electronic models is long. When the number of photovoltaics increases, the problem of time length is more serious. Therefore, it is necessary to conduct aggregation research on distributed photovoltaics. The aggregation of distributed photovoltaics can break through the limitation of hardware simulation speed, reduce the simulation time and the scale of the simulation system, and is also the research basis for system stability analysis and all other derived problems such as frequency regulation and voltage regulation.

SUMMARY OF THE INVENTION

The present invention provides a large-disturbance aggregation method for distributed photovoltaic power stations under the condition of electrical connection. Photovoltaic system, while effectively reducing the simulation time, can also ensure that the external power characteristics of photovoltaics before and after the equivalent value remain unchanged, and then provide a theoretical basis for the stability analysis of the system under large disturbances.

The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions:

A large-disturbance aggregation method for a distributed photovoltaic power station under the condition of electrical connection, characterized in that, based on the established pscad electromagnetic transient model of a single photovoltaic, including a photovoltaic square array model, a power generation unit step-up transformer, a power collection in the station The model of the line and the model of the inverter, including the following steps:

Step 1, according to the electrical position of the photovoltaic power station in the system and the voltage sag characteristics of each distributed photovoltaic power station when the fault occurs, group photovoltaics, specifically including:

Step 1.1, build the electrical position similarity matrix:

Retain photovoltaic nodes for equivalent simplification, eliminate non-photovoltaic nodes, and obtain the equivalent admittance matrix:

Y _G represents the admittance block of photovoltaic nodes connected with non-photovoltaic nodes, Y _P represents the admittance block of non-photovoltaic nodes, and Y _T represents the mutual admittance block between them.

Step 1.2, construct the voltage drop trajectory similarity matrix:

D _ij =∑(α(D _1ij )/ _{∑D 1ij} +(1-α)/∑D _2ij )

Among them, D _ij is the voltage drop track index, D _1ij is the voltage drop depth index, D _2ij is the voltage track index of the low voltage ride through, and α is the weight of the index.

The expression of the grouping matrix elements of the voltage dip depth index is:

D _1ij =max|Δv _i (t ₀ )−Δv _j (t ₀ )|

Δv _j and Δv _i are the different degrees of voltage drop of different photovoltaic inverters at time t ₀ :

Δv _k (t ₀ )=|v _k (t ₀ )-v _k0 |

Among them, v _k (t ₀ ) and v _k0 are the grid-connected voltage values of photovoltaic power station k at time t ₀ and steady state, respectively.

The grouped matrix element expression of the voltage trajectory index of low voltage ride through is:

Step 1.3, set the weight of each indicator:

After several experiments, the matrix similarity between the grouping matrix obtained by manual analysis and the similarity matrix of each influencing factor obtained by calculation was calculated, and the average value of the similarity was used as the weight of the corresponding index.

Among them, M _Aab is the manually judged grouping matrix, M _Bab is the grouping matrix obtained by each index, H is the number of rows of the grouping matrix, and W is the number of columns of the grouping matrix.

Step 1.4, perform grouping: perform grouping according to the characteristic distance of the column elements of the judgment matrix.

Step 2: Group PVs and lines in the same group to obtain the final aggregation model: PVs are aggregated according to capacity, and line impedances are aggregated according to the principle of constant power and voltage before and after the same value.

In the above-mentioned large disturbance aggregation method of a distributed photovoltaic power station under the condition of electrical connection, in the step 2, the method for grouping and aggregation of photovoltaics and lines in the same group is as follows:

Step 2.1, the photovoltaics in the same group aggregate the control parameters and filter circuit parameters according to the capacity weighting.

Step 2.2, the equivalent line impedance is aggregated to the original bus according to the principle that the power and voltage remain unchanged before and after the equivalent value:

为待合并光伏群的集电线路上引起的平均电压降落：Among them, S _PCC is the apparent power at the photovoltaic grid connection point, S _i is the apparent power on the line, M is the number of photovoltaics to be combined,

For the average voltage drop induced on the collector lines of the PV clusters to be combined:

Among them, ΔU _i is the voltage difference between the exit point of photovoltaic power station i and the grid-connected busbar.

In step 2.3, the photovoltaic power station with electrical connection is aggregated to the connection bus.

In the above-mentioned large-disturbance aggregation method of a distributed photovoltaic power station with electrical connections, the method for establishing a pscad electromagnetic transient model of a single photovoltaic is as follows:

并联的组件数为

光伏电池组件又由单体电池串并联而成，串联的单体电池数为

并联的单体电池数为

In step A, a model of the photovoltaic cell array is established. The photovoltaic cell array is composed of photovoltaic cell modules in series and parallel, and the number of modules in series is

The number of components connected in parallel is

Photovoltaic cell modules are made up of single cells in series and parallel, and the number of single cells in series is

The number of single cells connected in parallel is

In step B, a model of the filter circuit of the photovoltaic power station is established. The filter circuit in the station includes a series inductance L _f , a series resistance R _f , and a parallel capacitor C _f ;

Step C, establish the model of the inverter, that is, the d-axis current I _d and the q-axis current I _q output by the inverter during normal and low voltage ride-through:

是光伏发电站并网点电压标幺值；I_max是光伏发电站额定装机容量/(光伏并网点额定电压)；I_dn是光伏正常运行时输出的d轴电流；I_N是额定电流。in,

is the per-unit value of the grid-connected point voltage of the photovoltaic power station; I _max is the rated installed capacity of the photovoltaic power station/(rated voltage of the photovoltaic grid-connected point); I _dn is the d-axis current output during normal operation of the photovoltaic; I _N is the rated current.

Therefore, the present invention has the following advantages: 1. Aggregating a plurality of photovoltaic power stations into a small number of photovoltaic power stations, greatly reducing the simulation time and system scale; 2. The line aggregation considers both voltage loss and power loss, greatly improving accuracy; 3. The external characteristics of the photovoltaic power station before and after polymerization remain unchanged, which can provide a theoretical basis for subsequent protection schemes and control strategies.

Description of drawings

FIG. 1 is a structural diagram of a photovoltaic power station before equivalence adopted in the embodiment of the present invention.

FIG. 2 is a structural diagram of a photovoltaic power station in the No. 1 group after the equivalent value adopted in the embodiment of the present invention.

FIG. 3 is a graph of the output active power of the photovoltaic power station before and after the middle value according to the embodiment of the present invention.

FIG. 4 is a graph showing the output reactive power of the photovoltaic power station before and after the middle value according to the embodiment of the present invention.

Fig. 5 is a working flow chart of the present invention.

Detailed ways

The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings and calculation examples. It should be noted that the embodiments are exemplary and are used to explain the present invention, rather than being construed as limiting the present invention.

Example:

A method for large-disturbance aggregation of distributed photovoltaics under the condition of electrical connection, comprising the following steps:

Step 1. According to the national standard of photovoltaic low voltage ride-through and the measured inverter ride-through characteristics, establish a pscad electromagnetic transient model of a single photovoltaic. The specific operation methods are as follows:

Step 3: Group PVs and lines in the same group to obtain the final aggregation model: PVs are aggregated according to capacity, and line impedances are aggregated according to the principle that the power and voltage remain unchanged before and after the same value. The specific operation methods are as follows:

The specific operation method is as follows:

并联的组件数为

光伏电池组件又由单体电池串并联而成，串联的单体电池数为

并联的单体电池数为

Step 1.1, build a model of the photovoltaic cell array. The photovoltaic cell array is composed of photovoltaic cell modules in series and parallel, and the number of modules in series is

The number of components connected in parallel is

Photovoltaic cell components are made up of single cells in series and parallel, and the number of single cells in series is

The number of single cells connected in parallel is

Step 1.2, establish the model of the filter circuit of the photovoltaic power station. The filter circuit in the station includes a series inductance L _f , a series resistance R _f , and a parallel capacitor C _f ;

Step 1.3, establish the model of the inverter, that is, the d-axis current I _d and the q-axis current I _q output by the inverter during normal and low voltage ride-through:

是光伏发电站并网点电压标幺值；I_max是光伏发电站额定装机容量/(光伏并网点额定电压)；I_dn是光伏正常运行时输出的d轴电流；I_N是额定电流。in,

is the per-unit value of the grid-connected point voltage of the photovoltaic power station; I _max is the rated installed capacity of the photovoltaic power station/(rated voltage of the photovoltaic grid-connected point); I _dn is the d-axis current output during normal operation of the photovoltaic; I _N is the rated current.

Step 2, according to the electrical position of the photovoltaic power station in the system and the voltage drop characteristics of each distributed photovoltaic power station when the fault occurs, the photovoltaic power station is grouped, and the specific operation method is as follows:

According to the electrical position of the photovoltaic power station in the system and the voltage sag characteristics of each distributed photovoltaic power station at the time of failure, the photovoltaic power station is grouped, including:

Step 2.1, construct the electrical position similarity matrix:

Retain photovoltaic nodes for equivalent simplification, eliminate non-photovoltaic nodes, and obtain the equivalent admittance matrix:

Y _G represents the admittance block of photovoltaic nodes connected with non-photovoltaic nodes, Y _P represents the admittance block of non-photovoltaic nodes, and Y _T represents the mutual admittance block between them.

Step 2.2, construct the voltage drop trajectory similarity matrix:

D _ij =∑(α(D _1ij )/ _{∑D 1ij} +(1-α)/∑D _2ij )

Among them, D _ij is the voltage drop track index, D _1ij is the voltage drop depth index, D _2ij is the voltage track index of the low voltage ride through, and α is the weight of the index.

The expression of the grouping matrix elements of the voltage dip depth index is:

D _1ij =max|Δv _i (t ₀ )−Δv _j (t ₀ )|

Δv _j and Δv _i are the different degrees of voltage drop of different photovoltaic inverters at time t ₀ :

Δv _k (t ₀ )=|v _k (t ₀ )-v _k0 |

Among them, v _k (t ₀ ) and v _k0 are the grid-connected voltage values of photovoltaic power station k at time t ₀ and steady state, respectively.

The grouped matrix element expression of the voltage trajectory index of low voltage ride through is:

Step 2.3, set the weight of each indicator:

After several experiments, the matrix similarity between the grouping matrix obtained by manual analysis and the similarity matrix of each influencing factor obtained by calculation was calculated, and the average value of the similarity was used as the weight of the corresponding index.

Among them, M _Aab is the manually judged grouping matrix, M _Bab is the grouping matrix obtained by each index, H is the number of rows of the grouping matrix, and W is the number of columns of the grouping matrix.

Step 2.4, perform grouping: perform grouping according to the characteristic distance of the column elements of the judgment matrix.

For example, in the implemented calculation example, for the distribution network whose structure diagram is shown in Figure 1, the similarity results of the evaluation matrix obtained based on the above method are shown in Table 1:

Table 1 Evaluation matrix similarity results

The final clustering results are shown in Table 2, where only cluster 1 has electrical connections:

Table 2 Evaluation matrix similarity results

Step 3: Group PVs and lines in the same group to obtain the final aggregation model: PVs are aggregated according to capacity, and line impedances are aggregated according to the principle that the power and voltage remain unchanged before and after the same value. The specific operation methods are as follows:

Step 3.1, the photovoltaics in the same group aggregate the control parameters and filter circuit parameters according to the capacity weighting.

Step 3.2, the impedance of the equivalent line is aggregated to the original bus according to the principle that the power and voltage before and after the equivalent value remain unchanged:

为待合并光伏群的集电线路上引起的平均电压降落：Among them, S _PCC is the apparent power at the photovoltaic grid connection point, S _i is the apparent power on the line, M is the number of photovoltaics to be combined,

For the average voltage drop induced on the collector lines of the PV clusters to be combined:

Among them, ΔU _i is the voltage difference between the exit point of photovoltaic power station i and the grid-connected busbar.

Step 3.3, aggregate the photovoltaic power station with electrical connection to the connection bus.

The two photovoltaics in photovoltaic group 1 have obvious electrical connections. Figure 3 is the active power diagram of the photovoltaic output before and after polymerization, and Figure 4 is the reactive power diagram of the photovoltaic output before and after polymerization.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which the present invention pertains can make various modifications or additions to the described specific embodiments or substitute in similar manners, but will not deviate from the spirit of the present invention or go beyond the definition of the appended claims range.

Claims (3)

1. a large disturbance aggregation method of a distributed photovoltaic power station under the condition of electrical connection, it is characterized in that, based on the established single photovoltaic pscad electromagnetic transient model, including the model of photovoltaic square array, power generation unit step-up transformer, in-station The model of the collector circuit and the model of the inverter, including the following steps: Step 1, according to the electrical position of the photovoltaic power station in the system and the voltage sag characteristics of each distributed photovoltaic power station when the fault occurs, group photovoltaics, specifically including: Step 1.1, build the electrical position similarity matrix: Retain photovoltaic nodes for equivalent simplification, eliminate non-photovoltaic nodes, and obtain the equivalent admittance matrix:

Y _G represents the admittance block of photovoltaic nodes connected with non-photovoltaic nodes, Y _P represents the admittance block of non-photovoltaic nodes, and Y _T represents the mutual admittance block between them; Step 1.2, construct the voltage drop trajectory similarity matrix: D _ij =∑(α(D _1ij )/ _{∑D 1ij} +(1-α)/∑D _2ij ) Among them, D _ij is the voltage drop track index, D _1ij is the voltage drop depth index, D _2ij is the voltage track index of low voltage ride through, and α is the weight of the index; The expression of the grouping matrix elements of the voltage dip depth index is: D _1ij =max|Δv _i (t ₀ )−Δv _j (t ₀ )| Δv _j and Δv _i are the different degrees of voltage drop of different photovoltaic inverters at time t ₀ : Δv _k (t ₀ )=|v _k (t ₀ )-v _k0 | where v _k (t ₀ ) and v _k0 are the grid-connected voltage values of photovoltaic power station k at time t ₀ and steady state, respectively; The grouped matrix element expression of the voltage trajectory index of low voltage ride through is:

Step 1.3, set the weight of each indicator: After several experiments, the matrix similarity between the grouping matrix obtained by manual analysis and the similarity matrix of each influencing factor obtained by calculation was calculated, and the average value of the similarity was used as the weight of the corresponding index;

Among them, M _Aab is the manually judged grouping matrix, M _Bab is the grouping matrix obtained by each index, H is the number of rows of the grouping matrix, and W is the number of columns of the grouping matrix; Step 1.4, perform grouping: perform grouping according to the characteristic distance of the column elements of the judgment matrix; Step 2: Group PVs and lines in the same group to obtain the final aggregation model: PVs are aggregated according to capacity, and line impedances are aggregated according to the principle of constant power and voltage before and after the same value. 2 . The method for large disturbance aggregation of a distributed photovoltaic power station in the case of electrical connection according to claim 1 , wherein in the step 2, the method for grouping and aggregation of photovoltaics and lines in the same group is performed. 3 . as follows: Step 2.1, PVs in the same group aggregate control parameters and filter circuit parameters according to capacity weighting; Step 2.2, the equivalent line impedance is aggregated to the original bus according to the principle that the power and voltage remain unchanged before and after the equivalent value:

Among them, S _PCC is the apparent power at the photovoltaic grid connection point, S _i is the apparent power on the line, M is the number of photovoltaics to be combined,

For the average voltage drop induced on the collector lines of the PV clusters to be combined:

Among them, ΔU _i is the voltage difference between the exit point of photovoltaic power station i and the grid-connected bus; In step 2.3, the photovoltaic power station with electrical connection is aggregated to the connection bus. 3. the large disturbance aggregation method of a kind of distributed photovoltaic power station according to claim 1 in the case of electrical connection, it is characterized in that, the pscad electromagnetic transient model method of establishing single photovoltaic is as follows: Step A, establish a model of the photovoltaic cell array; the photovoltaic cell array is formed of photovoltaic cell components in series and parallel, and the number of components in series is

The number of components connected in parallel is

Photovoltaic cell modules are made up of single cells in series and parallel, and the number of single cells in series is

The number of single cells connected in parallel is

Step B, establishing a model of the filter circuit of the photovoltaic power station; the filter circuit in the station includes a series inductance L _f , a series resistance R _f , and a parallel capacitor C _f ; Step C, establish the model of the inverter, that is, the d-axis current I _d and the q-axis current I _q output by the inverter during normal and low voltage ride-through:

in,

is the voltage per unit at the grid-connected point of the photovoltaic power station; I _max is the rated installed capacity of the photovoltaic power station/(rated voltage of the photovoltaic grid-connected point); I _dn is the d-axis current output when the photovoltaic is in normal operation; _IN is the rated current.

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