Doubly-fed wind power plant series compensation line protection method based on differential current digital-form characteristics

Abstract

With the continuous increase of the access number of double-fed wind power plants and the continuous increase of the number of the double-fed wind power plants, the technology upgrade and scale expansion of a new energy power generation system for grid connection and the like, the complex fault characteristics of the new energy power generation system bring challenges to traditional relay protection, and consequently the performance of a traditional relay protection method is reduced and even refusal operation occurs. In order to solve the problem, the invention discloses a protection method based on the digital-form characteristic of the differential current. According to the protection method, numerical characteristics and shape characteristics of differential current are represented through a specific algorithm, so that the difference of current sequences at the two ends is reflected. According to the method, numerical value coefficients are constructed to identify internal and external faults, good reliability is shown in the face of various internal faults on a series compensation line of the doubly-fed wind power plant, and good tolerance is achieved for interference such as CT saturation, CT errors and abnormal data.

Description

Technical Field

[0001] The invention relates to a double-fed wind farm series compensation line protection method based on differential current digital-shape characteristics, and belongs to the technical field of power system relay protection. Background Art

[0002] Amid the accelerated construction of new power systems, the large-scale application and development of renewable energy provides a crucial guarantee for achieving the "carbon peak" and "carbon neutrality" goals on schedule. Among the many new energy power generation methods, wind power is one of the most mature and plays an increasingly important role in my country's energy structure. Among wind power generation equipment, the doubly fed induction generator (DFIG) is a relatively mature technology offering numerous advantages, including high efficiency, strong adaptability, high reliability, excellent controllability, and low maintenance costs. It is a key piece of wind power equipment. With technological advancements and the annual expansion of scale, it has demonstrated broad development potential and application prospects. Summary of the Invention

[0003] Aiming at the problem of performance degradation or even refusal to operate of existing traditional relay protection in double-fed wind farm series compensation lines, the present invention provides a double-fed wind farm series compensation line protection method based on differential current shape characteristics.

[0004] The protection method for series compensation lines of a doubly-fed wind farm based on the digital-shape characteristics of differential current includes the following steps:

[0005] Step 1: Sample the current on both sides of the series compensation line. The data window size is one sampling period, and the number of sampling points in the data window is N. T , get the sampling current point set i r and i g , for i r and i g Perform normalization operation to obtain point set i r ′ and i g ′; where the subscripts r and g represent the wind farm side and the grid side of the series compensation line respectively;

[0006] Step 2: Use the current sequences on both sides to calculate the differential current sequence i df and the normalized differential current sequence i dfn , delaying the two by a quarter cycle to obtain the delayed differential current i de and the normalized delayed differential current i den ;

[0007] Step 3: Calculate the numerical coefficient B v ;

[0008] Step 4: Determine the numerical coefficient B vIs it greater than or equal to the protection threshold B? vset , if it is greater than or equal to the protection threshold B vset Then go to step 5; if it is less than the protection threshold B vset It is determined to be an out-of-area fault; considering the reliability and safety of protection, B vset Set to 0.5;

[0009] Step 5: Get four special moments, among which in the first half of the data window: |i df (k)-i de (k)|The differential current i corresponding to the minimum moment clei and the delayed differential current is i cdlei ,|i df (k)-i de The differential current corresponding to the maximum moment of (k)| is i clea and the delayed differential current is i cdlea In the second half of the data window, we get: |i df (k)-i de (k)|The differential current i corresponding to the minimum moment clai and the delayed differential current is i cdlai ,|i df (k)-i de The differential current corresponding to the maximum moment of (k)| is i claa and the delayed differential current is i cdlaa The coefficient a is calculated using the differential current corresponding to the four special moments and the delayed differential current. ls and c ls ;

[0010] Step 6: Through a ls and c ls The left calculated eccentricity e l (k) and right calculate the eccentricity e r (k), and then calculate the shape coefficient B s ;

[0011] Step 7: Determine the shape factor B s Is it greater than or equal to the protection threshold B? sset , if it is greater than or equal to the protection threshold B sset It is determined to be an internal fault; if it is less than the protection threshold B sset It is determined to be an out-of-area fault; considering the reliability and safety of protection, B sset Set to 0.16.

[0012] The present invention discloses a protection method for a doubly-fed wind farm series compensation line based on the digital-shape characteristics of differential current. The method solves the problem of performance degradation or even refusal to operate of traditional relay protection in a doubly-fed wind farm series compensation line, and can ensure the correct operation of the doubly-fed wind farm series compensation line protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of the series compensation line of a doubly fed wind farm;

[0014] Figure 2 The flowchart of the protection method for series compensation lines in a doubly fed wind farm based on the differential current shape characteristics is shown in FIG. DETAILED DESCRIPTION

[0015] The present invention will be further described below with reference to the accompanying drawings.

[0016] The protection method for series compensation lines of a doubly-fed wind farm based on the digital-shape characteristics of differential current includes the following steps:

[0017] Step 1: If Figure 1 and Figure 2 , the current on both sides of the series compensation line is sampled, the data window size is one sampling period, and the number of sampling points in the data window is N T , get the sampling current point set i r and i g , for i r and i g Perform normalization operation to obtain point set i r ′ and i g ′; where the subscripts r and g represent the wind farm side and the grid side of the series compensation line respectively; the specific formula of the normalization operation process is as follows:

[0018]

[0019] Step 2: If Figure 2 , use the current sequences on both sides to find the differential current sequence i df and the normalized differential current sequence i dfn , delaying the two by a quarter cycle to obtain the delayed differential current i de and the normalized delayed differential current i den The specific formulas for differential current and normalized differential current are as follows:

[0020]

[0021] Step 3: If Figure 2 , calculate the numerical coefficient B v ; Calculate the numerical coefficient B v The specific formula is as follows:

[0022] D(k)=idfn (k) 2 +i den (k) 2 (3)

[0023]

[0024] Step 4: If Figure 2 , determine the numerical coefficient B v Is it greater than or equal to the protection threshold B? vset , if it is greater than or equal to the protection threshold B vset Then go to step 5; if it is less than the protection threshold B vset It is determined to be an out-of-area fault; considering the reliability and safety of protection, B vset Set to 0.5;

[0025] Step 5: If Figure 2 , and obtain four special moments, among which in the first half of the data window: |i df (k)-i de (k)|The differential current i corresponding to the minimum moment clei and the delayed differential current is i cdlei ,|i df (k)-i de The differential current corresponding to the maximum moment of (k)| is i clea and the delayed differential current is i cdlea In the second half of the data window, we get: |i df (k)-i de (k)|The differential current i corresponding to the minimum moment clai and the delayed differential current is i cdlai ,|i df (k)-i de The differential current corresponding to the maximum moment of (k)| is i claa and the delayed differential current is i cdlaa The coefficient a is calculated using the differential current corresponding to the four special moments and the delayed differential current. ls and c ls ; Calculate coefficient a ls and c ls The specific formula is as follows:

[0026]

[0027]

[0028] Step 6: If Figure 2 , through a ls and c ls The left calculated eccentricity e l (k) and right calculate the eccentricity er (k), and then calculate the shape coefficient B s ; Left calculation of eccentricity e l (k) and right calculate the eccentricity e r (k) and shape factor B s The specific formula is as follows:

[0029]

[0030]

[0031] Step 7: If Figure 2 , determine the shape coefficient B s Is it greater than or equal to the protection threshold B? sset , if it is greater than or equal to the protection threshold B sset It is determined to be an internal fault; if it is less than the protection threshold B sset It is determined to be an out-of-area fault; considering the reliability and safety of protection, B sset Set to 0.16.

[0032] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements, replacements, modifications and embellishments can be made without departing from the principles and purpose of the present invention. These improvements, replacements, modifications and embellishments should also be regarded as the scope of protection of the present invention.

[0033] The contents not described in detail in this specification belong to the prior art known to those skilled in the art.

Claims

1. A protection method for series compensation lines in a doubly-fed wind farm based on the differential current shape characteristic comprises the following steps: Step 1: Sample the current on both sides of the series compensation line. The data window size is one sampling period, and the number of sampling points in the data window is N. T , get the sampling current point set i r and i g , for i r and i g Perform normalization operation to obtain point set i r ′ and i g ′; where the subscripts r and g represent the wind farm side and the grid side of the series compensation line respectively; Step 2: Use the current sequences on both sides to calculate the differential current sequence i df and the normalized differential current sequence i dfn , delaying the two by a quarter cycle to obtain the delayed differential current i de and the normalized delayed differential current i den ; Step 3: Calculate the numerical coefficient B v ; Step 4: Determine the numerical coefficient B v Is it greater than or equal to the protection threshold B? vset , if it is greater than or equal to the protection threshold B vset Then go to step 5; if it is less than the protection threshold B vset It is determined to be an out-of-area fault; considering the reliability and safety of protection, B vset Set to 0.5; Step 5: Get four special moments, among which in the first half of the data window: |i df (k)-i de (k)|The differential current i corresponding to the minimum moment clei and the delayed differential current is i cdlei ,|i df (k)-i de The differential current corresponding to the maximum moment of (k)| is i clea and the delayed differential current is i cdlea In the second half of the data window, we get: |i df (k)-i de (k)|The differential current i corresponding to the minimum moment clai and the delayed differential current is i cdlai ,|i df (k)-i de The differential current corresponding to the maximum moment of (k)| is i claa and the delayed differential current is i cdlaa The coefficient a is calculated using the differential current corresponding to the four special moments and the delayed differential current. ls and c ls ; Step 6: Through a ls and c ls The left calculated eccentricity e l (k) and right calculate the eccentricity e r (k), and then calculate the shape coefficient B s ; Step 7: Determine the shape factor B s Is it greater than or equal to the protection threshold B? sset , if it is greater than or equal to the protection threshold B sset It is determined to be an internal fault; if it is less than the protection threshold B sset It is determined to be an out-of-area fault; considering the reliability and safety of protection, B sset Set to 0.

16.

2. The method for protecting a doubly-fed wind farm series compensation line based on differential current shape characteristics according to claim 1, characterized in that: The specific formula for the normalization operation process in step 1 is as follows:

3. The method for protecting a doubly-fed wind farm series compensation line based on differential current shape characteristics according to claim 1, characterized in that: The specific formulas for the differential current and normalized differential current in step 2 are as follows:

4. The method for protecting a doubly-fed wind farm series compensation line based on differential current shape characteristics according to claim 1, characterized in that: Calculate the numerical coefficient B as described in step 3 v The specific formula is as follows: D(k)=i dfn (k) 2 +i den (k) 2 (3) 5. The method for protecting a doubly-fed wind farm series compensation line based on differential current shape characteristics according to claim 1, characterized in that: Calculate the coefficient a as described in step 5 ls and c ls The specific formula is as follows:

6. The method for protecting a doubly-fed wind farm series compensation line based on differential current shape characteristics according to claim 1, characterized in that: Step 6: Calculate the eccentricity e l (k) and right calculate the eccentricity e r (k) and shape factor B s The specific formula is as follows:

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