CN105846408A - Pilot protection method for power distribution network having distributed DFIG type wind motor - Google Patents

Abstract

The invention discloses a pilot protection method for a power distribution network having a distributed DFIG type wind motor. The method comprises the following steps: fault current waveforms at protection installation places positioned at two ends of a line are extracted and analyzed, a Prony algorithm is applied to discrete data of currents, magnitude of attenuation factors of fault currents at the two ends is calculated, attenuation factor difference between the currents at the two ends under failure conditions can be obtained after the attenuation factors of the two ends are compared with each other, and whether an internal fault or an external fault occurs can be corrected determined after the attenuation factor difference is compared with a protection setting value. The method provided in the invention can effectively and reliably distinguish internal and external faults in the line, specific characteristics of a distributed power source can be effectively utilized, and the method has certain application value in practical engineering.

Description

Pilot protection method for power distribution network containing distributed DFIG type wind turbine

Technical Field

The invention belongs to the technical field of relay protection of power distribution networks, and particularly relates to a pilot protection method for a power distribution network containing distributed DFIG type wind turbines.

Background

After the wind driven generator is connected to the power distribution network, the power distribution network becomes a multi-source system, and particularly, the influence of the wind driven generator on the power distribution network is more obvious along with the increase of the wind power generation permeability; meanwhile, due to the randomness and uncertainty of the output of the wind driven generator, the traditional over-current protection is difficult to adapt, and the protection setting of the power distribution network is more difficult. In practical engineering applications, a double-fed Induction Generator (DFIG) is a mainstream model, and the fault characteristics of the double-fed wind turbine Generator are more complicated than those of an inverter distributed power supply, so that the double-fed wind turbine Generator is very important for the research on the fault transient characteristics of the double-fed wind turbine Generator.

At present, the protection method for the distributed power supply at home and abroad mainly comprises the following steps: (1) the method solves the problem of protection directivity caused by the access of a distributed power supply and avoids the situation of reverse misoperation of a protection element; (2) the fault location and analysis method is utilized to improve the protection of the power distribution network to a certain extent, and a certain effect is achieved; (3) the output capacity of the distributed power supply is limited to a certain extent, so that the original protection of the power distribution network is not influenced; (4) protection against transient characteristics of distributed power supplies. For (1), the discrimination of the multi-source fault direction is solved by utilizing the power direction, but the voltage quantity is used, and the discrimination is difficult to realize in an actual power distribution network. (2) The fault of the power distribution network is processed by utilizing a communication mode, and the reliability is relatively uncertain. The output capacity of the distributed power supply is limited in the step (3), which is not in line with the purpose of energy development in China. The last method is to study the transient characteristics of the distributed power source, but there is little to combine the transient characteristics of the doubly-fed wind generator with the protection of the distribution network.

Disclosure of Invention

The invention aims to provide a pilot protection method for a power distribution network containing distributed DFIG type wind turbines, and solves the problems that the protection method for the power distribution network connected with the DFIG is complex and cannot adapt to the transient characteristic of the DFIG in the prior art.

The technical scheme adopted by the invention is that the pilot protection method for the power distribution network containing the distributed DFIG type wind turbine is implemented according to the following steps:

step 1: respectively acquiring current values at a head-end circuit breaker and a tail-end circuit breaker through a head-end current transformer and a tail-end current transformer of a power distribution network of the DFIG type wind turbine, and respectively transmitting the measured current values to a head-end programmable processor and a tail-end programmable processor for data processing;

step 2: and respectively sending a regulating instruction to the head-end circuit breaker action controller and the tail-end circuit breaker action controller by the head-end programmable processor and the tail-end programmable processor according to the data processing result in the step 1 to control the head-end circuit breaker and the tail-end circuit breaker, thereby realizing the pilot protection method of the power distribution network of the DFIG type wind turbine.

The invention is also characterized in that:

the specific process of data processing in the step 1 is as follows:

step 1.1, calculating current attenuation factor values corresponding to current values of the head-end circuit breaker and the tail-end circuit breaker by using a Prony algorithm, and respectively recording the current attenuation factor values as α₁、α₂；

Step 1.2 calculation α₁、α₂The absolute value of the difference is compared with α_setAnd comparing to realize pilot protection of the line:

1) when | α₁-α₂|＞α_setJudging that the fault occurs between the lines, and the protection devices at two ends of the lines act to cut off the fault;

2) when | α₁-α₂|＜α_setIf the fault occurs outside the line, the protection devices at both ends of the line are not operated.

Step 1.1, calculating to obtain current attenuation factor values corresponding to current values of the head-end circuit breaker and the tail-end circuit breaker by adopting a Prony algorithm, wherein the specific process is as follows:

simulating different types of faults of the power distribution network through a PSCAD simulation experiment, importing the obtained fault current transient data into a matlab program, and calculating values of attenuation factors of current of a head-end circuit breaker and a tail-end circuit breaker under different faults through a Prony algorithm;

the principle of the Prony algorithm is as follows:

$\begin{array}{c}\hat{x}\left(n\right)=\underset{m=1}{\overset{p}{\Σ}}{b}_m{z}_m^n,\left(n=0,1,\mathrm{...},N-1,\mathrm{...}\right)\\ b_m=A_m\exp \left({\mathrm{j\θ}}_m\right)\\ z_m=\exp \[\left({\mathrm{\α}}_m+j2{\mathrm{\πf}}_m\right)\mathrm{\Δ}t\]\end{array}---\left(1\right)$

in the formula: n-number of sinusoidal components of the decomposition; p-the order of the Prony model; n is the number of sampled data points; a. the_mAmplitude α_m-a damping factor; f. of_m-the oscillation frequency; theta_m-a phase; Δ t-sampling interval;

the specific process of calculating the attenuation factor by using the principle comprises the following steps:

(1) defining:

$r(i,j)=\underset{n=p}{\overset{N-1}{\Σ}}x(n-j)x^{*}(n-i)---\left(2\right)$

in the formula: x is the number of^*(.) is the complex conjugate of x (.);

(2) and (3) constructing a matrix by utilizing fault current transient data obtained by a simulation test and combining a formula (2):

$R=\left[\begin{array}{cccc}r\left(1,0\right)& r\left(1,1\right)& \mathrm{...}& r\left(1,p_e\right)\\ r\left(2,0\right)& r\left(2,1\right)& & r\left(2,p_e\right)\\ \mathrm{...}& \mathrm{...}& & \mathrm{...}\\ \mathrm{...}& \mathrm{...}& & \mathrm{...}\\ r\left(p_e,0\right)& r\left(p_e,0\right)& \mathrm{...}& r\left(p_e,p_e\right)\end{array}\right],p_e>>p---\left(3\right)$

(3) determining autoregressive parameter a of R by SVD-TLS method₁,...,a_p；

(4) Solving a polynomial

1+a₁z^-1+...+a_pz^-p＝0 (4)

Root of Degen Z_i(i＝1,...,p)

(5) Calculating the parameter b

$\left[\begin{array}{cccc}1& 1& \mathrm{...}& 1\\ z_1& z_2& \mathrm{...}& z_p\\ .& .& & .\\ .& .& \mathrm{...}& .\\ .& .& & .\\ .& .& & .\\ .& .& \mathrm{...}& .\\ .& .& & .\\ z_1^{N-1}& z_2^{N-1}& \mathrm{...}& z_p^{N-1}\end{array}\right]\·\left[\begin{array}{c}{b}_1\\ b_2\\ .\\ .\\ .\\ .\\ .\\ .\\ b_p\end{array}\right]=\left[\begin{array}{c}\hat{x}\left(0\right)\\ \hat{x}\left(1\right)\\ .\\ .\\ .\\ .\\ .\\ .\\ \hat{x}\left(N-1\right)\end{array}\right]---\left(5\right)$

Wherein,

$\hat{x}\left(n\right)=\underset{i=1}{\overset{p}{\Σ}}{\mathrm{\α}}_i\hat{x}\left(n-i\right),n=0,1,2,\mathrm{...}N-1;$

then:

(6) calculating an attenuation factor α_i

α_i＝ln|z_i/Δt| (6)

Where i 1.

The power distribution network system of the DFIG type wind turbine comprises a power supply, wherein the power supply is connected with a first bus through a step-down transformer, a feeder line is led out from the first bus, a second bus is arranged on the feeder line, and a DFIG wind power plant is connected to the second bus through a first step-up transformer and a second step-up transformer; a head end breaker and a head end current transformer for detecting the current value at the head end breaker are arranged at an outlet of the first bus, the head end breaker is connected with a head end breaker action controller, and the head end current transformer and the head end breaker action controller are both connected with a head end programmable processor; and a tail end circuit breaker and a tail end current transformer for detecting the current value of the tail end circuit breaker are arranged at the outlet of the second bus, the tail end circuit breaker is connected with a tail end circuit breaker action controller, and the tail end current transformer and the tail end circuit breaker action controller are both connected with a tail end programmable processor.

The invention has the beneficial effects that: 1) the invention considers the inherent transient characteristic of the distributed power supply, can set the protection more accurately, can greatly improve the reliability and the selectivity of the protection of the distribution network connected with the DFIG; 2) the pilot protection is utilized in a double-power-supply mode, only the current amount is used, the calculation process is simpler, and compared with the traditional pilot protection, the pilot protection circuit has higher adaptability to a line with a branch line and high practicability in a power distribution network.

Drawings

FIG. 1 is a schematic diagram of a power distribution grid system for a DFIG type wind turbine according to the present invention;

FIG. 2 is a flow chart of a pilot protection method for a power distribution network according to the present invention;

fig. 3 is a schematic diagram of the fault current characteristics of the distribution network of a DFIG type wind turbine according to the present invention.

In the figure, 1 is a power supply, 2 is a step-down transformer, 3 is a first bus, 4 is a DFIG wind power plant, 5 is a second bus, 6 is a first step-up transformer, 7 is a second step-up transformer, 8 is a tail end breaker, 9 is a head end breaker, 10 is a tail end current transformer, 11 is a head end current transformer, 12 is a tail end programmable processor, 13 is a head end programmable processor, 14 is a tail end breaker action controller, and 15 is a head end breaker action controller.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

The distribution network system of the DFIG type wind turbine is structurally shown in figure 1 and comprises a power supply 1, wherein the power supply 1 is connected with a first bus 3 through a step-down transformer 2, a feeder line is led out from the first bus 3, a second bus 5 is arranged on the feeder line, and a DFIG wind power plant 4 is connected to the second bus 5 through a first step-up transformer 6 and a second step-up transformer 7; a head end circuit breaker 9 and a head end current transformer 11 for detecting the current value at the head end circuit breaker 9 are arranged at the outlet of the first bus 3, the head end circuit breaker 9 is connected with a head end circuit breaker action controller 15, and the head end current transformer 11 and the head end circuit breaker action controller 15 are both connected with a head end programmable processor 13; a tail end breaker 8 and a tail end current transformer 10 for detecting the current value of the tail end breaker 8 are arranged at the outlet of the second bus 5, the tail end breaker 8 is connected with a tail end breaker action controller 14, and the tail end current transformer 10 and the tail end breaker action controller 14 are both connected with a tail end programmable processor 12.

The invention discloses a pilot protection method for a power distribution network containing distributed DFIG type wind turbines, which is implemented according to the following steps, wherein the flow is shown in figure 2:

step 1: the current value of head end circuit breaker 9, end circuit breaker 8 department is gathered respectively to head end current transformer 11, the end current transformer 10 through the distribution network of DFIG type wind-powered electricity generation machine to transmit the current value that records respectively to head end programmable processor 13, end programmable processor 12, carry out data processing, concrete process is:

step 1.1, calculating current attenuation factor values corresponding to current values of the head-end breaker 9 and the tail-end breaker 8 by using a Prony algorithm, and respectively recording the current attenuation factor values as α₁、α₂The specific process is as follows:

simulating different types of faults of the power distribution network through a PSCAD simulation experiment, importing the obtained fault current transient data into a matlab program, and calculating values of attenuation factors of current of a head-end circuit breaker and a tail-end circuit breaker under different faults through a Prony algorithm;

the principle of the Prony algorithm is as follows:

$\begin{array}{c}\hat{x}\left(n\right)=\underset{m=1}{\overset{p}{\Σ}}{b}_m{z}_m^n,\left(n=0,1,\mathrm{...},N-1,\mathrm{...}\right)\\ b_m=A_m\exp \left({\mathrm{j\θ}}_m\right)\\ z_m=\exp \[\left({\mathrm{\α}}_m+j2{\mathrm{\πf}}_m\right)\mathrm{\Δ}t\]\end{array}---\left(1\right)$

in the formula: n-number of sinusoidal components of the decomposition; p-the order of the Prony model; n is the number of sampled data points; a. the_mAmplitude α_m-a damping factor; f. of_m-the oscillation frequency; theta_m-a phase; Δ t-sampling interval;

the specific process of calculating the attenuation factor by using the principle comprises the following steps:

(1) defining:

$r(i,j)=\underset{n=p}{\overset{N-1}{\Σ}}x(n-j)x^{*}(n-i)---\left(2\right)$

in the formula: x is the number of^*(.) is the complex conjugate of x (.);

(2) and (3) constructing a matrix by utilizing fault current transient data obtained by a simulation test and combining a formula (2):

$R=\left[\begin{array}{cccc}r\left(1,0\right)& r\left(1,1\right)& \mathrm{...}& r\left(1,p_e\right)\\ r\left(2,0\right)& r\left(2,1\right)& & r\left(2,p_e\right)\\ \mathrm{...}& \mathrm{...}& & \mathrm{...}\\ \mathrm{...}& \mathrm{...}& & \mathrm{...}\\ r\left(p_e,0\right)& r\left(p_e,0\right)& \mathrm{...}& r\left(p_e,p_e\right)\end{array}\right],p_e>>p---\left(3\right)$

(3) determining autoregressive parameter a of R by SVD-TLS method₁,...,a_p；

(4) Solving a polynomial

1+a₁z^-1+...+a_pz^-p＝0 (4)

Root of Degen Z_i(i＝1,...,p)

(5) Calculating parameter b (5)

$\left[\begin{array}{cccc}1& 1& \mathrm{...}& 1\\ z_1& z_2& \mathrm{...}& z_p\\ .& .& & .\\ .& .& \mathrm{...}& .\\ .& .& & .\\ .& .& & .\\ .& .& \mathrm{...}& .\\ .& .& & .\\ z_1^{N-1}& z_2^{N-1}& \mathrm{...}& z_p^{N-1}\end{array}\right]\·\left[\begin{array}{c}{b}_1\\ b_2\\ .\\ .\\ .\\ .\\ .\\ .\\ b_p\end{array}\right]=\left[\begin{array}{c}\hat{x}\left(0\right)\\ \hat{x}\left(1\right)\\ .\\ .\\ .\\ .\\ .\\ .\\ \hat{x}\left(N-1\right)\end{array}\right]---\left(5\right)$

Wherein,

$\hat{x}\left(n\right)=\underset{i=1}{\overset{p}{\Σ}}{\mathrm{\α}}_i\hat{x}\left(n-i\right),n=0,1,2,\mathrm{...}N-1;$

then:

(6) calculating an attenuation factor α_i

α_i＝ln|z_i/Δt| (6)

Where i 1.

Step 1.2 calculation α₁、α₂The absolute value of the difference is compared with α_setAnd comparing to realize pilot protection of the line:

1) when | α₁-α₂|＞α_setJudging that the fault occurs between the lines, and the protection devices at two ends of the lines act to cut off the fault;

2) when | α₁-α₂|＜α_setIf the fault occurs outside the line, the protection devices at both ends of the line are not operated.

Step 2: and the head end programmable processor 13 and the tail end programmable processor 12 respectively send a regulation and control instruction to the head end breaker action controller 15 and the tail end breaker action controller 14 according to the data processing result in the step 1 to control the head end breaker 9 and the tail end breaker 8, so that the pilot protection method of the power distribution network of the DFIG type wind turbine is realized.

Example (b):

step 1: taking the fault current of the three-phase earth fault output by the DFIG wind power plant shown in fig. 3(a) and the fault current of the large power supply shown in fig. 3(b) under the three-phase earth fault as an example, the algorithm time window is selected to be 20ms in consideration of the rapidity of protection. And filtering the current waveform to filter out serious waveform distortion points.

Step 2, using the Prony algorithm to calculate attenuation factors of the data to obtain the magnitude of the corresponding attenuation factor α₁、α₂。

Step 3, solve | α₁-α₂The value of | is noted as Δ α.

Step 4. taking into account the actual measurement error, α is set here_setProgram calculation results are shown in table 1, where 0.5:

TABLE 1 protection discrimination results

As can be seen from the above table, if Δ α is greater than 0.5, the protection can operate correctly.

And 5: the results of a number of tests on protection with different capacities are shown in table 2:

table 2 results of a number of tests for protection

From the above table, it can be known that the pilot protection method for the power distribution network can correctly act.

Claims (4)

1. A pilot protection method for a power distribution network containing distributed DFIG type wind turbines is characterized by being implemented according to the following steps:

step 1: respectively acquiring current values of a head end breaker (9) and a tail end breaker (8) through a head end current transformer (11) and a tail end current transformer (10) of a power distribution network of the DFIG type wind turbine, and respectively transmitting the measured current values to a head end programmable processor (13) and a tail end programmable processor (12) for data processing;

step 2: and the head end programmable processor (13) and the tail end programmable processor (12) respectively send a regulation and control instruction to the head end circuit breaker action controller (15) and the tail end circuit breaker action controller (14) according to the data processing result in the step 1 to control the head end circuit breaker (9) and the tail end circuit breaker (8), so that the pilot protection method of the power distribution network of the DFIG type wind turbine is realized.

2. The pilot protection method for the power distribution network containing the distributed DFIG type wind turbine generator as claimed in claim 1, wherein the specific data processing process in step 1 is as follows:

step 1.1, calculating current attenuation factor values corresponding to current values of a head-end circuit breaker (9) and a tail-end circuit breaker (8) by adopting a Prony algorithm, and respectively recording the current attenuation factor values as α₁、α₂；

Step 1.2 calculation α₁、α₂The absolute value of the difference is compared with α_setAnd comparing to realize pilot protection of the line:

1) when | α₁-α₂|＞α_setJudging that the fault occurs between the lines, and the protection devices at two ends of the lines act to cut off the fault;

2) when | α₁-α₂|＜α_setIf the fault occurs outside the line, the protection devices at both ends of the line are not operated.

3. The pilot protection method for the power distribution network containing the distributed DFIG type wind turbines as recited in claim 2, wherein the step 1.1 adopts a Prony algorithm to calculate and obtain current attenuation factor values corresponding to current values at a head-end breaker (9) and a tail-end breaker (8), and the specific process is as follows:

simulating different types of faults of the power distribution network through a PSCAD simulation experiment, importing the obtained fault current transient data into a matlab program, and calculating values of attenuation factors of current of a head-end circuit breaker and a tail-end circuit breaker under different faults through a Prony algorithm;

the principle of the Prony algorithm is as follows:

$\hat{x}\left(n\right)=\underset{m=1}{\overset{p}{\Σ}}{b}_m^n{z}_m,(n=0,1,...,N-1,...)$

b_m＝A_mexp(jθ_m) (1)

z_m＝exp[(α_m+j2πf_m)Δt]

in the formula: n-number of sinusoidal components of the decomposition; p-the order of the Prony model; n is the number of sampled data points; a. the_mAmplitude α_m-a damping factor; f. of_m-the oscillation frequency; theta_m-a phase; Δ t-sampling interval;

the specific process of calculating the attenuation factor by using the principle comprises the following steps:

(1) defining:

$r(i,j)=\underset{n=p}{\overset{N-1}{\Σ}}x(n-j)x^{*}(n-i)---\left(2\right)$

in the formula: x is the number of^*(.) is the complex conjugate of x (.);

(2) and (3) constructing a matrix by utilizing fault current transient data obtained by a simulation test and combining a formula (2):

$R=\left[\begin{array}{cccc}r\left(1,0\right)& r\left(1,1\right)& \mathrm{...}& r\left(1,p_e\right)\\ r\left(2,0\right)& r\left(2,1\right)& & r\left(2,p_e\right)\\ \mathrm{...}& \mathrm{...}& & \mathrm{...}\\ \mathrm{...}& \mathrm{...}& & \mathrm{...}\\ r\left(p_e,0\right)& r\left(p_e,0\right)& \mathrm{...}& r\left(p_e,p_e\right)\end{array}\right],p_e>>p---\left(3\right)$

(3) determining autoregressive parameter a of R by SVD-TLS method₁,...,a_p；

(4) Solving a polynomial

1+a₁z^-1+...+a_pz^-p＝0 (4)

Root of Degen Z_i(i＝1,...,p)

(5) Calculating the parameter b

$\left[\begin{array}{cccc}1& 1& \mathrm{...}& 1\\ z_1& z_2& \mathrm{...}& z_p\\ .& .& & .\\ .& .& \mathrm{...}& .\\ .& .& & .\\ .& .& & .\\ .& .& \mathrm{...}& .\\ .& .& & .\\ z_1^{N-1}& z_2^{N-1}& \mathrm{...}& z_p^{N-1}\end{array}\right]\·\left[\begin{array}{c}{b}_1\\ b_2\\ .\\ .\\ .\\ .\\ .\\ .\\ b_p\end{array}\right]=\left[\begin{array}{c}\hat{x}\left(0\right)\\ \hat{x}\left(1\right)\\ .\\ .\\ .\\ .\\ .\\ .\\ \hat{x}\left(N-1\right)\end{array}\right]---\left(5\right)$

Wherein,

$\hat{x}\left(n\right)=\underset{i=1}{\overset{p}{\Σ}}{\mathrm{\α}}_i\hat{x}\left(n-i\right),n=0,1,2,\mathrm{...}N-1;$

then:

(6) calculating an attenuation factor α_i

α_i＝ln|z_i/Δt| (6)

Where i 1.

4. The power distribution network pilot protection method containing the distributed DFIG type wind turbines is characterized in that the power distribution network system of the DFIG type wind turbines comprises a power supply (1), the power supply (1) is connected with a first bus (3) through a step-down transformer (2), a feeder line is led out from the first bus (3), a second bus (5) is arranged on the feeder line, and a DFIG wind power plant (4) is connected to the second bus (5) through a first step-up transformer (6) and a second step-up transformer (7); a head end breaker (9) and a head end current transformer (11) for detecting the current value of the head end breaker (9) are arranged at the outlet of the first bus (3), the head end breaker (9) is connected with a head end breaker action controller (15), and the head end current transformer (11) and the head end breaker action controller (15) are both connected with a head end programmable processor (13); and a tail end breaker (8) and a tail end current transformer (10) for detecting the current value of the tail end breaker (8) are arranged at the outlet of the second bus (5), the tail end breaker (8) is connected with a tail end breaker action controller (14), and the tail end current transformer (10) and the tail end breaker action controller (14) are both connected with a tail end programmable processor (12).