A method for accurate time synchronization of distribution network fault indicators based on acquisition system

Abstract

The present invention proposes a method for accurate time synchronization of a distribution network fault indicator based on a collection system. The collection system includes a collection unit and a collection unit. The collection unit first calculates the frequency deviation change rate of the collection unit, calculates the frequency deviation change rate clock error of the collection unit according to the frequency deviation change rate of the collection unit, and calculates the maximum interval time for sending the synchronization time data frame of the collection unit according to the frequency deviation change rate of the collection unit; then adjusts the period of the broadcast time synchronization data frame of the collection unit according to the real-time effective value of the distribution line current; finally, within the period of the broadcast time synchronization data frame, the time of sending the synchronization time data frame request and response between the collection unit and the collection unit is calculated by the maximum likelihood estimation algorithm, and the phase deviation and frequency deviation of the collection unit within the period of the broadcast time synchronization data frame are estimated, and the initial phase and clock frequency of the collection unit within the period of the broadcast time synchronization data frame are corrected.

Description

Technical Field

[0001] The invention belongs to the technical field of distribution network, and in particular relates to a distribution network fault indicator accurate time synchronization method based on an acquisition system. Background Art

[0002] The distribution network is the link in the power system that directly faces users and has a direct impact on the reliability of power supply to users. The distribution line is an important part of the distribution network. It has many topological branches and a harsh operating environment. Once a fault occurs, it is difficult to quickly locate the fault, which seriously affects the improvement of power supply reliability.

[0003] As an important part of the distribution automation system, the distribution network fault indicator can be easily mounted on the distribution line. Once a short circuit fault or single-phase grounding fault occurs, the distribution network fault can be located.

[0004] The distribution network fault indicator system consists of a background positioning system, a collection unit, and a collection unit. In order to achieve accurate and reliable fault positioning, each collection unit and each collection unit and the three matching collection units must meet precise time synchronization to ensure the accuracy of synchronous sampling of each phase current and zero-sequence current synthesis.

[0005] In the distribution network fault indicator system, each collection unit directly uses high-power time synchronization technology, such as GPS / Beidou, to achieve accurate time synchronization. The traditional practice for each collection unit and its three matching collection units is that the collection unit broadcasts the synchronization time data frame regularly. After receiving the broadcast synchronization time frame, the three matching collection units perform their own time calibration to complete time synchronization. The field operation results show that:

[0006] After adopting the traditional time synchronization method, the time synchronization error between each collection unit and the three matching acquisition units is about 100 milliseconds;

[0007] The current at the end and branch of the distribution line cannot meet the requirements of regular time synchronization between the collection unit and the collection unit due to the small line load current.

[0008] At this time, the distribution network fault indicator system cannot achieve high-precision fault section positioning based on transient current sampling values. Summary of the invention

[0009] The purpose of the present invention is to provide a distribution network fault indicator precise time synchronization method based on an acquisition system, which can be used to significantly improve the time synchronization accuracy between each collection unit and its three matching acquisition units in the distribution network fault indicator system, so as to overcome the problems existing in the background technology.

[0010] In order to achieve the above object, the technical solution of the present invention is:

[0011] The collection system comprises: a collection unit and a collection unit;

[0012] The collection unit is connected to the acquisition unit wirelessly;

[0013] The distribution network fault indicator accurate time synchronization method comprises the following steps:

[0014] Step 1: The acquisition unit is used to collect the real-time current of the distribution line in real time and transmit it wirelessly to the collection unit; the collection unit calculates the real-time effective value of the distribution line current according to the real-time current of the distribution line;

[0015] Step 2: The collection unit calculates the frequency deviation change rate of the collection unit, calculates the frequency deviation change rate clock error of the collection unit according to the frequency deviation change rate of the collection unit, calculates the maximum interval time for sending the synchronization time data frame of the collection unit according to the frequency deviation change rate of the collection unit, and sets the period of the broadcast time synchronization data frame of the collection unit according to the real-time effective value of the distribution line current and the maximum interval time for sending the synchronization time data frame of the collection unit;

[0016] Step 3: within the period of the broadcast time synchronization data frame, the collection unit sends a synchronization time data frame request to the collection unit, and after receiving the synchronization time data frame request, the collection unit further sends a synchronization time data frame response to the collection unit; the time of sending the synchronization time data frame request and response is calculated by the maximum likelihood estimation algorithm to obtain an estimate of the phase deviation and frequency deviation of the collection unit within the period of the broadcast time synchronization data frame, and correct the initial phase and clock frequency of the collection unit within the period of the broadcast time synchronization data frame;

[0017] Preferably, the real-time current of the distribution line in step 1 is:

[0018] X(1),X(2),X(3),X(4),…,X(N Ts )

[0019] Where X(k) represents the current of the distribution line at time k, N Ts represents the number of sampling moments, k∈[1,N Ts ];

[0020] The real-time effective value of the distribution line current calculated in step 1 is:

[0021]

[0022] In the formula, X(k) represents the current of the distribution line at time k, and X(eq) represents the real-time effective value of the current of the distribution line;

[0023] Preferably, the frequency deviation change rate of the calculation acquisition unit in step 2 is:

[0024] The collecting unit and the collecting unit are respectively connected at t i ,t i+1 ,t i+2 Perform clock synchronization;

[0025] Then the acquisition unit is at Δt i+1 =t i+1 -t i The time offset caused by frequency deviation in a time period is expressed as:

[0026] θ(t i+1 )=[T'(t i+1 )-T'(t i )]-(t i+1 -t i )

[0027] In the above formula, t i+1 represents the time of the aggregation unit during the i+1th clock synchronization process, t i represents the time of the collection unit in the i-th clock synchronization process, T'(t i+1 ) represents the time of the acquisition unit during the i+1th clock synchronization process; T'(t i ) represent the time of the acquisition unit during the i-th clock synchronization process;

[0028] The acquisition unit is at Δt i+2 =t i+2 -t i+1 The time offset caused by frequency deviation in a time period is expressed as:

[0029] θ(t i+2 )=[T'(t i+2 )-T'(t i+1 )]-(t i+2 -t i+1 )

[0030] In the above formula, t i+2 represents the time of the aggregation unit during the i+2th clock synchronization process, t i+1 represents the time of the collection unit during the i+1th clock synchronization process, T'(t i+2 ) represents the time of the acquisition unit during the i+2th clock synchronization process, T'(t i+1 ) represents the time of the acquisition unit during the i+1th clock synchronization process;

[0031] The frequency deviation change rate of the acquisition unit in step 2 is:

[0032]

[0033] Wherein, γ represents the frequency deviation change rate of the acquisition unit in step 2;

[0034] The frequency deviation change rate clock error of the acquisition unit calculated in step 2 is:

[0035]

[0036] In the above formula, T op represents the running time period, and e represents the clock error;

[0037] The maximum interval time for sending the synchronization time data frame of the calculation collection unit in step 2 is:

[0038]

[0039] In the above formula, T int.max Indicates the maximum interval time for the synchronous time data frame of the acquisition unit to send, E L.max Represents the minimum requirement for accurate fault location on the time synchronization error between the distribution network fault indicator aggregation unit and the acquisition unit;

[0040] The period of the broadcast time synchronization data frame of the aggregation unit is set as follows:

[0041]

[0042] In the above formula, T int.per represents the period of the broadcast time synchronization data frame of the aggregation unit, X(eq) represents the real-time effective value of the distribution line current, I L.min It indicates the minimum current flowing through the corresponding distribution line when the fault indicator acquisition unit is working normally, I L.max Indicates the maximum current flowing through the corresponding distribution line when the fault indicator acquisition unit is working normally, T int.min represents the minimum period of the aggregation unit broadcasting time synchronization data frame, X(eq) represents the real-time effective value of the distribution line current;

[0043] Preferably, in step 3, the time of sending the synchronization time data frame request and response is calculated by the maximum likelihood estimation algorithm, and the estimation of the phase deviation and frequency deviation of the acquisition unit within the broadcast time synchronization data frame period is obtained as follows:

[0044] According to the communication process between the collection unit and the acquisition unit, the time T is obtained. 1,i+1 and T 4,i+1 The calculation expression is:

[0045] T 1,i+1 =T 2,i+1 -dx i+1 +θ B,i+1 (T 2,i+1 -T4,i -dx i+1 )+θ A,i+1

[0046] =(1+θ B,i+1 )(T 2,i+1 -T 4,i -dx i+1 )+θ A,i+1 +T 4,i

[0047] T 4,i+1 =T 3,i+1 +d+y i+1 +θ B,i+1 (T 3,i+1 -T 4,i +d+y i+1 )+θ A,i+1

[0048] =(1+θ B,i+1 )(T 3,i+1 -T 4,i +d+y i+1 )+θ A,i+1 +T 4,i

[0049] In the above formula, during the (i+1)th clock synchronization process, the time when the acquisition unit responds to the synchronization time data frame to the collection unit is T 1,i+1 The time when the collection unit receives the synchronization time data frame from the collection unit is T 2,i+1 , and send the synchronous time data frame to the acquisition unit. This moment is T 3,i+1 ; The time when the acquisition unit receives the synchronization time data frame sent back by the collection unit is T 4,i+1 At the same time, the proposed estimation method also needs to use the time T when the acquisition unit receives the synchronization time data frame sent back by the collection unit during the i-th clock synchronization process. 4,i ; d represents the deterministic part of the path delay; x i+1 It represents the uncertain part of the path delay when the acquisition unit sends the synchronization data frame to the collection unit during the i+1th clock synchronization process, which generally obeys random distribution; θ A,i+1 represents the initial clock phase deviation between the collection unit and the acquisition unit during the i+1th clock synchronization process; θ B,i+1 represents the frequency deviation between the collection unit and the acquisition unit during the i+1th clock synchronization process, θ B,i+1 (T 1,i+1 -T 4,i +d+x i+1 ) represents the clock deviation caused by frequency deviation; y i+1It represents the uncertain part of the path delay when the aggregation unit sends the synchronization data frame to the acquisition unit during the i+1th clock synchronization process, which generally also obeys random distribution.

[0050] Let S1 = T 1,i+1 -T 4,i ; S2 = T 2,i+1 -T 4,i ; S3 = T 3,i+1 -T 4,i ; S4 = T 4,i+1 -T 4,i ; Using the maximum likelihood estimation method, the initial clock phase deviation θ between the collection unit and the acquisition unit in the i+1th clock synchronization process is obtained A,i+1 and frequency deviation θ B,i+1 expression:

[0051]

[0052]

[0053] In the above formula, d represents the deterministic part of the path delay, and the calculation formula is d = L dis / vc,L dis represents the distance between the collection unit and the acquisition unit, and vc represents the communication speed, which is generally taken as 3×10 8 m / s.

[0054] Step 3, in which the initial phase and clock frequency of the acquisition unit are corrected within the broadcast time synchronization data frame period, is specifically:

[0055] The initial phase deviation θ between the collection unit and the acquisition unit in the i+1th clock synchronization process is obtained. A,i+1 , adjust the clock signal phase of the acquisition unit to θ rev,i+1 =θ init,i+1 +θ A,i+1 , to ensure synchronization, where θ init,i+1 is the initial phase of the acquisition unit during the i+1th clock synchronization process, θ rev,i+1 is the phase of the acquisition unit after adjustment in the i+1th clock synchronization process; the clock frequency deviation θ between the collection unit and the acquisition unit in the i+1th clock synchronization process is obtained B,i+1 , adjust the clock frequency of the acquisition unit to f rev,i+1 =f init,i+1 +θ B,i+1 , where f init,i+1 is the initial clock frequency of the acquisition unit during the i+1th clock synchronization process, f rev,i+1is the clock frequency adjusted by the collection unit in the (i+1)th clock synchronization process. Finally, accurate time synchronization between the collection unit and the collection unit is achieved within the cycle of each broadcast time synchronization data frame.

[0056] Therefore, the present invention has the following advantages:

[0057] The proposed precise time synchronization method for distribution network fault indicators is based on the calculated frequency deviation change rate between the clocks of the aggregation unit and the collection unit, as well as the load current flowing through the distribution line. It adaptively adjusts the synchronization period of the broadcast time synchronization data frame between the aggregation unit and the collection unit, which can greatly improve the time synchronization accuracy between the aggregation unit and the collection unit while ensuring the normal power supply of the collection unit.

[0058] The proposed precise time synchronization method for distribution network fault indicators uses the maximum likelihood estimation method to obtain the clock initial phase deviation and frequency deviation between the aggregation unit and the acquisition unit at the starting time of each synchronization period within the time synchronization period between the aggregation unit and the acquisition unit. The acquisition unit clock is corrected based on this, which can greatly improve the precise time synchronization accuracy between the aggregation unit and the acquisition unit within each adaptive synchronization period. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 :Flow chart of accurate time synchronization of distribution network fault indicator proposed by the method of the present invention

[0060] Figure 2 : Schematic diagram of the clock synchronization principle between the distribution network fault indicator collection unit and the collection unit within the broadcast time synchronization data frame period proposed by the method of the present invention.

[0061] Figure 3 : Schematic diagram of the distribution network fault indicator aggregation unit and the collection unit proposed by the method of the present invention broadcasting time synchronization data frames for the i, i+1, and i+2 times.

[0062] Figure 4 : The principle of the synchronization process of the distribution network fault indicator collection unit and the collection unit proposed by the method of the present invention. DETAILED DESCRIPTION

[0063] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0064] Combine the following Figures 1 to 4 The specific implementation modes of the present invention are introduced.

[0065] The system of the present invention comprises: a collection unit and a collection unit;

[0066] The collection unit is connected to the acquisition unit wirelessly;

[0067] The acquisition unit is selected as follows: an inductive power transient recording type fault indicator acquisition unit containing a 433MHz wireless communication module;

[0068] The selection of the collection unit is: a fault indicator collection unit including a 433MHz wireless communication module, a GPS module, a 2G / 4G communication module, and a light storage power supply module;

[0069] A method for accurate time synchronization of a distribution network fault indicator, characterized in that it includes:

[0070] Step 1: The acquisition unit is used to collect the real-time current of the distribution line in real time and transmit it wirelessly to the collection unit; the collection unit calculates the real-time effective value of the distribution line current according to the real-time current of the distribution line;

[0071] The real-time current of the distribution line in step 1 is:

[0072] X(1),X(2),X(3),X(4),…,X(N Ts )

[0073] Where X(k) represents the current of the distribution line at time k, N Ts =1024 represents the number of sampling moments, k∈[1,N Ts ];

[0074] The real-time effective value of the distribution line current calculated in step 1 is:

[0075]

[0076] In the formula, X(k) represents the current of the distribution line at time k, and X(eq) represents the real-time effective value of the current of the distribution line. It is calculated that X(eq) = 30A at this time;

[0077] Step 2: The collection unit calculates the frequency deviation change rate of the collection unit, calculates the frequency deviation change rate clock error of the collection unit according to the frequency deviation change rate of the collection unit, calculates the maximum interval time for sending the synchronization time data frame of the collection unit according to the frequency deviation change rate of the collection unit, and sets the period of the broadcast time synchronization data frame of the collection unit according to the real-time effective value of the distribution line current and the maximum interval time for sending the synchronization time data frame of the collection unit;

[0078] The frequency deviation change rate of the acquisition unit calculated in step 2 is:

[0079] The collecting unit and the collecting unit are respectively connected at t i ,t i+1 ,t i+2 Perform clock synchronization; the time of the collection unit is t i = 12 hours 30 minutes 53 seconds 867.5 microseconds, t i+1 = 12 hours 40 minutes 54 seconds 865.6 microseconds, t i+2 = 12 hours 50 minutes 54 seconds 880.5 microseconds, the time of the acquisition unit is T'(t i )=12 hours 30 minutes 53 seconds 862.5 microseconds, T'(t i+1 )=12 hours 40 minutes 54 seconds 861.6 microseconds, T'(t i+2 ) = 12 hours 50 minutes 54 seconds 877.8 microseconds.

[0080] Then the acquisition unit is at Δt i+1 =t i+1 -t i = The time offset caused by frequency deviation in the time period of 10 minutes, 0 seconds, 99998.1 microseconds: θ(t i+1 )=T'(t i+1 )-T'(t i )-Δt i+1 =1 microsecond; the acquisition unit is at Δt i+2 =t i+2 -t i+1 The time offset caused by frequency deviation in the time period: θ(t i+2 )=1.3 microseconds.

[0081] The frequency deviation change rate of the acquisition unit in step 2 is:

[0082]

[0083] Set the requirements for the time synchronization accuracy of the three acquisition units for accurate fault location E L.max Take 20 microseconds, and the maximum interval time for sending the synchronization time data frame of the acquisition unit in step 2 is calculated as:

[0084]

[0085] The calculation process of setting the period of the broadcast time synchronization data frame of the aggregation unit in step 2 includes: L.min Indicates the minimum current flowing through the corresponding distribution line when the fault indicator acquisition unit can work normally, which is taken as 3A; I L.max It indicates the current flowing through the corresponding distribution line when the induction power energy of the fault indicator acquisition unit reaches the maximum value, which is taken as 600A; T int.minIndicates the minimum period of the aggregation unit broadcasting time synchronization data frame, which is generally taken as 5 minutes, that is, 300s. Then, the aggregation unit and the three matching collection units adaptively adjust the period T of the aggregation unit broadcasting time synchronization data frame according to the current flowing through the distribution line. int.per for:

[0086]

[0087] In the above formula, X(eq) represents the real-time effective value of the distribution line current. If it is equal to 30A at this time, the period T of the broadcast time synchronization data frame of the aggregation unit is adaptively adjusted. int.per It is 6597s.

[0088] Step 3: within the period of the broadcast time synchronization data frame, the collection unit sends a synchronization time data frame request to the collection unit, and after receiving the synchronization time data frame request, the collection unit further sends a synchronization time data frame response to the collection unit; the time of sending the synchronization time data frame request and response is calculated by the maximum likelihood estimation algorithm to obtain an estimate of the phase deviation and frequency deviation of the collection unit within the period of the broadcast time synchronization data frame, and correct the initial phase and clock frequency of the collection unit within the period of the broadcast time synchronization data frame;

[0089] In step 3, the maximum likelihood estimation algorithm is used to calculate the time of sending the synchronization time data frame request and response, and the phase deviation and frequency deviation estimation of the acquisition unit within the broadcast time synchronization data frame period are obtained as follows:

[0090] According to the communication process between the collection unit and the acquisition unit, the time T is obtained. 1,i+1 and T 4,i+1 The calculation expression is:

[0091] T 1,i+1 =T 2,i+1 -dx i+1 +θ B,i+1 (T 2,i+1 -T 4,i -dx i+1 )+θ A,i+1

[0092] =(1+θ B,i+1 )(T 2,i+1 -T 4,i -dx i+1 )+θ A,i+1 +T 4,i

[0093] T 4,i+1 =T 3,i+1 +d+y i+1 +θ B,i+1 (T3,i+1 -T 4,i +d+y i+1 )+θ A,i+1

[0094] =(1+θ B,i+1 )(T 3,i+1 -T 4,i +d+y i+1 )+θ A,i+1 +T 4,i

[0095] In the above formula, during the (i+1)th clock synchronization process, the time when the acquisition unit responds to the synchronization time data frame to the collection unit is T 1,i+1 The time when the collection unit receives the synchronization time data frame from the collection unit is T 2,i+1 , and send the synchronous time data frame to the acquisition unit. This moment is T 3,i+1 ; The time when the acquisition unit receives the synchronization time data frame sent back by the collection unit is T 4,i+1 At the same time, the proposed estimation method also needs to use the time T when the acquisition unit receives the synchronization time data frame sent back by the collection unit during the i-th clock synchronization process. 4,i ; d represents the deterministic part of the path delay; x i+1 It represents the uncertain part of the path delay when the acquisition unit sends the synchronization data frame to the collection unit during the i+1th clock synchronization process, which generally obeys random distribution; θ A,i+1 represents the initial clock phase deviation between the collection unit and the acquisition unit during the i+1th clock synchronization process; θ B,i+1 represents the frequency deviation between the collection unit and the acquisition unit during the i+1th clock synchronization process, θ B,i+1 (T 1,i+1 -T 4,i +d+x i+1 ) represents the clock deviation caused by frequency deviation; y i+1 It represents the uncertain part of the path delay when the aggregation unit sends the synchronization data frame to the acquisition unit during the i+1th clock synchronization process, which generally also obeys random distribution. In the actual process, it is measured that T 1,i+1 = 12 hours 40 minutes 54 seconds 865.400 microseconds; T 2,i+1 = 12 hours 40 minutes 54 seconds 865.402 microseconds; T 3,i+1 = 12 hours 40 minutes 54 seconds 865.403 microseconds; T 4,i+1 = 12 hours 40 minutes 54 seconds 865.404 microseconds; T 4,i =12 hours, 30 minutes, 53 seconds, 867.500 microseconds.

[0096] Let S1 = T 1,i+1 -T 4,i; S2 = T 2,i+1 -T 4,i ; S3 = T 3,i+1 -T 4,i ; S4 = T 4,i+1 -T 4,i ; Then, S1 = T 1,i+1 -T 4,i =10 minutes 999997.900 microseconds; S2 = T 2,i+1 -T 4,i =10 minutes 999997.902 microseconds; S3 = T 3,i+1 -T 4,i =10 minutes 999997.903 microseconds; S4 = T 4,i+1 -T 4,i = 10 minutes 999997.904 microseconds. Calculate the deterministic part d of the path delay, d = L dis / vc=3.33×10 -9 s, L dis represents the distance between the collection unit and the acquisition unit, 1 m; vc represents the communication speed, which is 3×10 8 m / s.

[0097] Using the maximum likelihood estimation method, the initial clock phase deviation θ between the collection unit and the acquisition unit in the i+1th clock synchronization process is obtained: A,i+1 and frequency deviation θ B,i+1 expression:

[0098]

[0099]

[0100] Step 3, in which the initial phase and clock frequency of the acquisition unit are corrected within the broadcast time synchronization data frame period, is specifically:

[0101] The initial phase deviation θ between the collection unit and the acquisition unit in the i+1th clock synchronization process is obtained. A,i+1 , adjust the clock signal phase of the acquisition unit to θ rev,i+1 =θ init,i+1 +θ A,i+1 , to ensure synchronization, where θ init,i+1 is the initial phase of the acquisition unit during the i+1th clock synchronization process, θ rev,i+1 is the phase of the acquisition unit after adjustment in the i+1th clock synchronization process; the clock frequency deviation θ between the collection unit and the acquisition unit in the i+1th clock synchronization process is obtained B,i+1 , adjust the clock frequency of the acquisition unit to f rev,i+1 =f init,i+1 +θ B,i+1 , where finit,i+1 is the initial clock frequency of the acquisition unit during the i+1th clock synchronization process, f rev,i+1 is the clock frequency adjusted by the collection unit in the (i+1)th clock synchronization process. Finally, accurate time synchronization between the collection unit and the collection unit is achieved within the cycle of each broadcast time synchronization data frame.

[0102] The above specific examples are used to illustrate the present invention, which is only used to help understand the present invention and is not intended to limit the present invention. For technicians in the technical field to which the present invention belongs, some simple deductions, deformations or substitutions can also be made based on the ideas of the present invention. It is easy for technicians in this field to understand that the above is only a preferred embodiment of the present invention patent, and is not intended to limit the present invention patent. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention patent should be included in the protection scope of the present invention patent.

Claims

1. A distribution network fault indicator accurate time synchronization method based on an acquisition system, characterized in that: The collection system comprises: a collection unit and a collection unit; The collection unit is connected to the acquisition unit wirelessly; The distribution network fault indicator accurate time synchronization method comprises the following steps: Step 1: The acquisition unit is used to collect the real-time current of the distribution line in real time and transmit it wirelessly to the collection unit; the collection unit calculates the real-time effective value of the distribution line current according to the real-time current of the distribution line; Step 2: The collection unit calculates the frequency deviation change rate of the collection unit, calculates the frequency deviation change rate clock error of the collection unit according to the frequency deviation change rate of the collection unit, calculates the maximum interval time for sending the synchronization time data frame of the collection unit according to the frequency deviation change rate of the collection unit, and sets the period of the broadcast time synchronization data frame of the collection unit according to the real-time effective value of the distribution line current and the maximum interval time for sending the synchronization time data frame of the collection unit; Step 3: Within the period of the broadcast time synchronization data frame, the collection unit sends a synchronization time data frame request to the collection unit. After receiving the synchronization time data frame request, the collection unit further sends a synchronization time data frame response to the collection unit; the time of sending the synchronization time data frame request and response is calculated through the maximum likelihood estimation algorithm to obtain an estimate of the phase deviation and frequency deviation of the collection unit within the period of the broadcast time synchronization data frame, and correct the initial phase and clock frequency of the collection unit within the period of the broadcast time synchronization data frame.

2. The distribution network fault indicator accurate time synchronization method based on the acquisition system according to claim 1 is characterized in that: The real-time current of the distribution line in step 1 is: X(1),X(2),X(3),X(4),……,X(N Ts ) Where X(k) represents the current of the distribution line at time k, N Ts represents the number of sampling moments, k∈[1,N Ts ]; The real-time effective value of the distribution line current calculated in step 1 is: Where X(k) represents the current of the distribution line at time k, and X(eq) represents the real-time effective value of the current of the distribution line.

3. The distribution network fault indicator accurate time synchronization method based on the acquisition system according to claim 1 is characterized in that: The frequency deviation change rate of the calculation acquisition unit in step 2 is: The collecting unit and the collecting unit are respectively connected at t i ,t i+1 ,t i+2 Perform clock synchronization; Then the acquisition unit is at Δt i+1 =t i+1 -t i The time offset caused by frequency deviation in a time period is expressed as: θ(t i+1 )=[T'(t i+1 )-T'(t i )]-(t i+1 -t i ) In the above formula, t i+1 represents the time of the aggregation unit during the i+1th clock synchronization process, t i represents the time of the collection unit in the i-th clock synchronization process, T'(t i+1 ) represents the time of the acquisition unit during the i+1th clock synchronization process; T'(t i ) represent the time of the acquisition unit during the i-th clock synchronization process; The acquisition unit is at Δt i+2 =t i+2 -t i+1 The time offset caused by frequency deviation in a time period is expressed as: θ(t i+2 )=[T'(t i+2 )-T'(t i+1 )]-(t i+2 -t i+1 ) In the above formula, t i+2 represents the time of the aggregation unit during the i+2th clock synchronization process, t i+1 represents the time of the collection unit during the i+1th clock synchronization process, T'(t i+2 ) represents the time of the acquisition unit during the i+2th clock synchronization process, T'(t i+1 ) represents the time of the acquisition unit during the i+1th clock synchronization process; The frequency deviation change rate of the acquisition unit in step 2 is: Wherein, γ represents the frequency deviation change rate of the acquisition unit in step 2; The frequency deviation change rate clock error of the acquisition unit calculated in step 2 is: In the above formula, T op represents the running time period, and e represents the clock error; The maximum interval time for sending the synchronization time data frame of the calculation collection unit in step 2 is: In the above formula, T int.max Indicates the maximum interval time for the synchronous time data frame of the acquisition unit to send, E L.max Represents the minimum requirement for accurate fault location on the time synchronization error between the distribution network fault indicator aggregation unit and the acquisition unit; The period of the broadcast time synchronization data frame of the aggregation unit is set as follows: In the above formula, T int.per represents the period of the broadcast time synchronization data frame of the aggregation unit, X(eq) represents the real-time effective value of the distribution line current, I L.min It indicates the minimum current flowing through the corresponding distribution line when the fault indicator acquisition unit is working normally, I L.max Indicates the maximum current flowing through the corresponding distribution line when the fault indicator acquisition unit is working normally, T int.min It represents the minimum period of the aggregation unit broadcasting time synchronization data frame, and X(eq) represents the real-time effective value of the distribution line current.

4. The distribution network fault indicator accurate time synchronization method based on the acquisition system according to claim 1 is characterized in that: In step 3, the maximum likelihood estimation algorithm is used to calculate the time of sending the synchronization time data frame request and response, and the phase deviation and frequency deviation estimation of the acquisition unit within the broadcast time synchronization data frame period are obtained as follows: According to the communication process between the collection unit and the acquisition unit, the time T is obtained. 1,i+1 and T 4,i+1 The calculation expression is: T 1,i+1 =T 2,i+1 -d-x i+1 +θ B,i+1 (T 2,i+1 -T 4,i -d-x i+1 )+θ A,i+1 =(1+θ B,i+1 )(T 2,i+1 -T 4,i -d-x i+1 )+θ A,i+1 +T 4,i T 4,i+1 =T 3,i+1 +d+y i+1 +θ B,i+1 (T 3,i+1 -T 4,i +d+y i+1 )+θ A,i+1 =(1+θ B,i+1 )(T 3,i+1 -T 4,i +d+y i+1 )+θ A,i+1 +T 4,i In the above formula, during the i+1th clock synchronization process, the time when the acquisition unit responds to the synchronization time data frame to the collection unit is T 1,i+1 The time when the collection unit receives the synchronization time data frame from the collection unit is T 2,i+1 , and send the synchronous time data frame to the acquisition unit. This moment is T 3,i+1 ; The time when the acquisition unit receives the synchronization time data frame sent back by the collection unit is T 4,i+1 At the same time, the proposed estimation method also needs to use the time T when the acquisition unit receives the synchronization time data frame sent back by the collection unit during the i-th clock synchronization process. 4,i ; d represents the determined part of the path delay; x i+1 represents the uncertain part of the path delay when the acquisition unit sends the synchronization data frame to the aggregation unit during the i+1th clock synchronization process, which obeys the random distribution; θ A,i+1 represents the initial clock phase deviation between the collection unit and the acquisition unit during the i+1th clock synchronization process; θ B,i+1 represents the frequency deviation between the collection unit and the acquisition unit during the i+1th clock synchronization process, θ B,i+1 (T 1,i+1 -T 4,i +d+x i+1 ) represents the clock deviation caused by frequency deviation; y i+1 It represents the uncertain part of the path delay when the aggregation unit sends the synchronization data frame to the acquisition unit during the i+1th clock synchronization process, which also obeys the random distribution; Let S1 = T 1,i+1 -T 4,i ; Let S2 = T 2,i+1 -T 4,i ; Let S3 = T 3,i+1 -T 4,i ; Let S4 = T 4,i+1 -T 4,i ; Using the maximum likelihood estimation method, the initial clock phase deviation θ between the collection unit and the acquisition unit in the i+1th clock synchronization process is obtained: A,i+1 and frequency deviation θ B,i+1 expression: In the above formula, d represents the deterministic part of the path delay, and the calculation formula is d = L dis / vc,L dis represents the distance between the collection unit and the acquisition unit, vc represents the communication speed, which is 3×10 8 m / s; Step 3, in which the initial phase and clock frequency of the acquisition unit are corrected within the broadcast time synchronization data frame period, is specifically: The initial phase deviation θ between the collection unit and the acquisition unit in the i+1th clock synchronization process is obtained. A,i+1 , adjust the clock signal phase of the acquisition unit to θ rev,i+1 =θ init,i+1 +θ A,i+1 , to ensure synchronization, where θ init,i+1 is the initial phase of the acquisition unit during the i+1th clock synchronization process, θ rev,i+1 is the phase of the acquisition unit after adjustment in the i+1th clock synchronization process; the clock frequency deviation θ between the collection unit and the acquisition unit in the i+1th clock synchronization process is obtained B,i+1 , adjust the clock frequency of the acquisition unit to f rev,i+1 =f init,i+1 +θ B,i+1 , where f init,i+1 is the initial clock frequency of the acquisition unit during the i+1th clock synchronization process, f rev,i+1 It is the clock frequency adjusted by the collection unit during the (i+1)th clock synchronization process; and finally, accurate time synchronization between the collection unit and the collection unit is achieved within the cycle of each broadcast time synchronization data frame.

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