CN105846408B - Power distribution network longitudinal protection method containing distributed DFIG types wind turbine - Google Patents

Abstract

The invention discloses a distribution network longitudinal protection method including a distributed DFIG type wind motor, which comprises the following steps: extracting and analyzing the fault current waveform at the protection installation place at both ends of the line, and calculating the discrete data of the current through the Prony algorithm The size of the attenuation factor of the fault current at both ends, and compare the attenuation factors at both ends to obtain the difference of the attenuation factor of the current at both ends in the case of a fault, and compare it with the setting value of the protection, which can correctly determine the difference between the fault area and the fault. Out of zone failure. The method provided by the invention can effectively and reliably distinguish faults inside and outside the circuit, can effectively utilize the unique properties of distributed power sources, and has certain application value in actual engineering.

Description

Pilot protection method for distribution network with distributed DFIG type wind turbines

technical field

The invention belongs to the technical field of distribution network relay protection, and in particular relates to a distribution network longitudinal protection method including a distributed DFIG type wind motor.

Background technique

After the wind turbines are connected to the distribution network, the distribution network becomes a multi-source system, especially as the penetration rate of wind power generation increases, making its impact on the distribution network more obvious; at the same time, due to the random output of wind turbines The characteristics and uncertainties make it difficult to adapt to the traditional overcurrent protection, which makes the protection setting of distribution network more difficult. In practical engineering applications, the doubly-fed induction generator (DFIG, Doubly-fed Induction Generator) is the mainstream model, and the fault characteristics of the doubly-fed wind turbine are more complicated than that of the inverter distributed power supply. Therefore, the study of its fault transient characteristics is very important.

At present, there are mainly protection methods for distributed power sources at home and abroad: (1) A directional overcurrent protection scheme is proposed, which solves the protection direction problem caused by the access of distributed power sources and avoids the protection (2) Using fault location and analysis methods to improve the distribution network protection, and achieved certain results; (3) To limit the output capacity of distributed power, So that it will not affect the original protection of the distribution network; (4) Protection for the transient characteristics of the distributed power supply. For (1), it uses the power direction to solve the multi-source fault direction discrimination, but it uses the voltage quantity, which is difficult to realize in the actual distribution network. In (2), the communication method is used to deal with the faults of the distribution network, which has great uncertainty in terms of reliability. Limiting the output capacity of distributed power in (3) does not meet the country's purpose of energy development. Although the last one studies the transient characteristics of distributed power generation, there is almost no aspect of combining the transient characteristics of doubly-fed wind turbines with distribution network protection.

Contents of the invention

The purpose of the present invention is to provide a distribution network longitudinal protection method containing distributed DFIG type wind generators, which solves the temporary problem of complex protection methods for distribution networks connected with DFIG and inability to adapt to DFIG in the prior art. The problem of state characteristics.

The technical scheme adopted in the present invention is a method for longitudinal connection protection of distribution network including distributed DFIG type wind motor, which is specifically implemented according to the following steps:

Step 1: Collect the current values at the head-end circuit breaker and the end-end circuit breaker respectively through the head-end current transformer and end-end current transformer of the distribution network of the DFIG wind turbine, and transmit the measured current values to the head-end respectively Programmable processor, terminal programmable processor for data processing;

Step 2: The head-end programmable processor and the end-end programmable processor send control instructions to the head-end circuit breaker action controller and the end-end circuit breaker action controller to control the head-end circuit breaker and the end circuit breaker respectively according to the data processing results of step 1 , to realize the longitudinal protection method of the distribution network of the DFIG type wind turbine.

The present invention is also characterized in that:

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

Step 1.1: first use the Prony algorithm to calculate the current attenuation factor values corresponding to the current values at the head-end circuit breaker and the end-end circuit breaker, which are recorded as α ₁ and α ₂ respectively;

Step 1.2: Calculate the difference between α ₁ and α ₂ , and compare the absolute value of the difference with α _set to realize the longitudinal protection of the line:

1) When |α ₁ -α ₂ |＞α _set , it is judged that the fault occurs between the lines, and the protection devices at both ends of the line act to cut off the fault;

2) When |α ₁ -α ₂ |<α _set , it is judged that the fault occurs outside the line, and the protection devices at both ends of the line do not operate.

Step 1.1 Use the Prony algorithm to calculate the current attenuation factor value corresponding to the current value at the head-end circuit breaker and the end-end circuit breaker. The specific process is as follows:

Through the PSCAD simulation experiment, different types of faults in the distribution network are simulated, and the obtained fault current transient data is imported into the matlab program, and the values of the attenuation factors of the head-end circuit breaker and the end-end circuit breaker current under different faults are calculated through the Prony algorithm;

The principle of the Prony algorithm is as follows:

In the formula: n—number of sine components decomposed; p—order of Prony model; N—number of sampling data points; A _m —amplitude; α _m —damping factor; f _m —oscillation frequency; θ _m —phase ;Δt—sampling interval;

The specific process of calculating the attenuation factor using the above principles is as follows:

(1) Definition:

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

(2) Using the fault current transient data obtained from the simulation test, combined with the formula (2), the matrix is constructed:

(3) Use the SVD-TLS method to determine the autoregressive parameters a ₁ ,...,a _p of R;

(4) Solving polynomials

1+a ₁ z ^-1 +...+a _p z ^-p = 0 (4)

Get the root z _i (i=1,...,p)

(5) Calculation parameter b

in,

but:

(6) Calculate the attenuation factor α _i

α _i =ln|z _i /Δt| (6)

where i=1,...,p.

The distribution network system of the DFIG type wind turbine includes a power supply, the power supply is connected to the first busbar through a step-down transformer, a feeder line is drawn from the first busbar, and a second busbar is set on the feeder line, and the DFIG wind farm passes through the first step-up transformer 1. The second step-up transformer is connected to the second busbar; at the exit of the first busbar, a headend circuit breaker and a headend current transformer for detecting the current value at the headend circuit breaker are arranged, and the headend circuit breaker is connected with the headend The circuit breaker action controller is connected, and the head-end current transformer and the head-end circuit breaker action controller are connected to the head-end programmable processor; the end circuit breaker is installed at the second bus outlet to detect the current value at the end circuit breaker The terminal current transformer, the terminal circuit breaker is connected with the terminal circuit breaker action controller, and the terminal current transformer and the terminal circuit breaker action controller are connected with the terminal programmable processor.

The beneficial effects of the present invention are: 1) the present invention takes into account the inherent transient characteristics of the distributed power supply, and can be more accurate for the setting of the protection, and can greatly improve the reliability and selectivity of the protection of the distribution network connected with the DFIG; 2) In the form of dual power supply, the longitudinal protection is used, and only the current is used, and the calculation process is relatively simple. Compared with the traditional longitudinal protection, it has higher adaptability to lines with branch lines. It has high practicability in distribution network.

Description of drawings

Fig. 1 is the structural representation of the distribution network system of DFIG type wind generator among the present invention;

Fig. 2 is the flowchart of distribution network longitudinal protection method of the present invention;

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

In the figure, 1. Power supply, 2. Step-down transformer, 3. First busbar, 4. DFIG wind farm, 5. Second busbar, 6. First step-up transformer, 7. Second step-up transformer, 8. Terminal Circuit breaker, 9. Head end circuit breaker, 10. End current transformer, 11. Head end current transformer, 12. End programmable processor, 13. Head end programmable processor, 14. End circuit breaker action controller , 15. Head-end circuit breaker action controller.

Detailed ways

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

The distribution network system of DFIG type wind generator in the present invention, structure as shown in Figure 1, comprises power supply 1, and power supply 1 is connected with the first bus bar 3 through step-down transformer 2, draws a feeder line from the first bus bar 3 place, in the feeder line There is a second bus 5 on the top, and the DFIG wind farm 4 is connected to the second bus 5 through the first step-up transformer 6 and the second step-up transformer 7; a head-end circuit breaker 9 is set at the exit of the first bus 3 and the head-end current transformer 11 for detecting the current value at the head-end circuit breaker 9, the head-end circuit breaker 9 is connected with the head-end circuit breaker action controller 15, the head-end current transformer 11 and the head-end circuit breaker action controller 15 Both are connected to the head-end programmable processor 13; at the exit of the second bus 5, a terminal circuit breaker 8 and a terminal current transformer 10 for detecting the current value at the terminal circuit breaker 8 are arranged, and the terminal circuit breaker 8 and the terminal circuit breaker are controlled The terminal current transformer 10 and the terminal circuit breaker action controller 14 are both connected to the terminal programmable processor 12 .

According to the present invention, a distribution network longitudinal protection method containing distributed DFIG type wind motors, the process flow is shown in Figure 2, and it is specifically implemented according to the following steps:

Step 1: through the head-end current transformer 11 and the end-end current transformer 10 of the distribution network of the DFIG type wind turbine, respectively collect the current values at the head-end circuit breaker 9 and the end-end circuit breaker 8, and record the measured current values respectively Transfer to the head-end programmable processor 13 and the end programmable processor 12 for data processing, the specific process is:

Step 1.1: First use the Prony algorithm to calculate the current attenuation factor values corresponding to the current values at the head circuit breaker 9 and the end circuit breaker 8, which are recorded as α ₁ and α ₂ respectively. The specific process is as follows:

Through the PSCAD simulation experiment, different types of faults in the distribution network are simulated, and the obtained fault current transient data is imported into the matlab program, and the values of the attenuation factors of the head-end circuit breaker and the end-end circuit breaker current under different faults are calculated through the Prony algorithm;

The principle of the Prony algorithm is as follows:

In the formula: n—number of sine components decomposed; p—order of Prony model; N—number of sampling data points; A _m —amplitude; α _m —damping factor; f _m —oscillation frequency; θ _m —phase ;Δt—sampling interval;

The specific process of calculating the attenuation factor using the above principles is as follows:

(1) Definition:

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

(2) Using the fault current transient data obtained from the simulation test, combined with the formula (2), the matrix is constructed:

(3) Use the SVD-TLS method to determine the autoregressive parameters a ₁ ,...,a _p of R;

(4) Solving polynomials

1+a ₁ z ^-1 +...+a _p z ^-p = 0 (4)

Get the root z _i (i=1,...,p)

(5) Calculation parameter b(5)

in,

but:

(6) Calculate the attenuation factor α _i

α _i =ln|z _i /Δt| (6)

where i=1,...,p.

Step 1.2: Calculate the difference between α ₁ and α ₂ , and compare the absolute value of the difference with α _set to realize the longitudinal protection of the line:

1) When |α ₁ -α ₂ |＞α _set , it is judged that the fault occurs between the lines, and the protection devices at both ends of the line act to cut off the fault;

2) When |α ₁ -α ₂ |<α _set , it is judged that the fault occurs outside the line, and the protection devices at both ends of the line do not operate.

Step 2: The head-end programmable processor 13 and the end-end programmable processor 12 respectively issue control instructions to the head-end circuit breaker action controller 15 and the end-end circuit breaker action controller 14 according to the data processing results of step 1 to control the head-end circuit breaker 9. The terminal circuit breaker 8 realizes the longitudinal protection method of the distribution network of the DFIG type wind generator.

Example:

Step 1: Take the fault current of the DFIG wind farm output under the three-phase ground fault shown in Figure 3(a) and the fault current of the large power supply under the three-phase ground fault shown in Figure 3(b) as examples for testing , the algorithm time window takes into account the rapidity of protection, choose 20ms. Filter the current waveform to filter out severe waveform distortion points.

Step 2: Use the above-mentioned Prony algorithm to calculate the attenuation factors of the above data, and obtain the respective corresponding attenuation factors as α ₁ and α ₂ .

Step 3: Find the value of |α ₁ -α ₂ |, denoted as Δα.

Step 4: Considering the actual measurement error, set α _set = 0.5 here, and the calculation results of the program are shown in Table 1:

Table 1 Protection discrimination results

It can be seen from the above table that Δα>0.5, the protection can operate correctly.

Step 5: A large number of test results for protection under different capacities are shown in Table 2:

Table 2 A large number of test results of protection

It can be known from the above table that the method for longitudinal protection of the distribution network of the present invention can operate correctly.

Claims (3)

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;

the specific process of the data processing is as follows:

step 1.1, calculating current attenuation factor values corresponding to current values at 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 of alpha₁、α₂difference between the absolute value of the difference and alpha_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_setJudging that the fault occurs outside the line and the protection devices at two ends of the line do not act;

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 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:

in the formula: n-number of sinusoidal components of the decomposition; p-the order of the Prony model; n-number of samplesThe number of data points; a. the_mamplitude alpha_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:

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):

(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

Wherein,

then:

(6) calculating the attenuation factor alpha_i

α_i＝ln|z_i/Δt| (6)

Where i 1.

3. 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).