Fault collaborative control method and system for power distribution network in neutral point low resistance grounding system

Abstract

The present invention relates to a coordinated control method and system for faults in a power distribution network of a neutral point low-resistance grounding system, the coordinated control method including a voltage oscillation and harmonic excess control method and a single-phase grounding fault identification method. On the one hand, the present invention can control the output voltage when voltage oscillation and harmonics occur during the operation of a power distribution network of a neutral point low-resistance grounding system through the voltage oscillation and harmonic excess control method, thereby improving the operation stability and safety. On the other hand, through the single-phase grounding fault identification method, the single-phase grounding fault and the faulty phase can be determined through the high similarity between the phase current and the zero-sequence current, thereby improving the accuracy of determination and identification.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrified railways, and in particular relates to a method and system for coordinated control of power distribution network faults in a neutral point low-resistance grounding system. Background Art

[0002] The power electronics of the power system is the direction of future power system development, because power electronics has flexible control capabilities and can effectively control various system parameters, states, trends, power quality, etc. Therefore, it has become a trend for power systems, including distribution networks, to move towards power electronics, and many types of power electronic equipment have been used in distribution networks. In particular, power router equipment has been widely used from high voltage to low voltage.

[0003] However, the applicant found that: in the actual application process, there are still many problems, such as: the oscillation problem of the power electronic system, the problem of controlling the harmonic load, and the problem of satisfying various types of neutral point operation modes of the existing distribution system, especially the problem of handling single-phase grounding faults under the neutral point operation mode. Because in the field of power distribution, single-phase grounding faults have become a common fault among many faults, it is very necessary to solve the oscillation and harmonic problems of the distribution network in the power electronic system, as well as the identification of single-phase grounding faults. Summary of the invention

[0004] In order to solve the above-mentioned problems existing in the prior art, the present invention provides a coordinated control method and system for a distribution network fault in a neutral point low-resistance grounding system, which can control the output voltage when voltage oscillation and harmonics occur during the operation of the distribution network in the neutral point low-resistance grounding system, and can determine single-phase grounding faults and faulty phases through the high similarity between phase current and zero-sequence current.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The invention discloses a method for coordinated control of power distribution network faults in a neutral point low resistance grounding system, which is used in a single power supply operation network powered by a high voltage power electronic power supply, and includes a voltage oscillation and harmonic over-limit control method and a single-phase grounding fault identification method;

[0007] The voltage oscillation and harmonic excess control method described herein cuts off the connection between the power supply and the network when the power supply voltage of the distribution network oscillates, and performs the magnitude calculation of the harmonic distribution and harmonic frequency when the power supply voltage of the distribution network does not oscillate, and reverses and superimposes the harmonic frequency exceeding the standard on the power supply voltage control instruction to control the output voltage;

[0008] The single-phase grounding fault identification method calculates the current error frequency sum between the phase current and the zero-sequence current of each phase and the frequency sum of the square of the phase current and the zero-sequence current of each phase according to the change of the phase current and the zero-sequence current of each phase on the power supply side of the distribution network, and then calculates the similarity between the phase current and the zero-sequence current of each phase to determine whether there is a single-phase grounding fault and the fault phase.

[0009] In a possible design, the voltage oscillation and harmonic excess control method specifically includes:

[0010] S101. Collecting power supply voltage of power distribution network;

[0011] S102. Voltage oscillation judgment: determine whether the system has voltage oscillation according to the collected power supply voltage of the power distribution network. If oscillation occurs, cut off the power supply and network connection; if no oscillation occurs, execute S103;

[0012] S103. Calculate harmonic components: perform harmonic distribution and harmonic frequency calculations on the collected power supply voltage of the distribution network to obtain harmonic components;

[0013] S104. Screening excessive harmonic frequency signals: judging whether the harmonic components obtained in S103 exceed the requirements of the set power quality standard, and executing S105 for the harmonic frequencies exceeding the set power quality standard;

[0014] S105. Superimpose harmonic frequency signal: compare the excessive harmonic frequency filtered by S104 with the control and sampling frequency of the power supply. When the 10 times excessive harmonic frequency is less than or equal to the control and sampling frequency of the power supply, the signal of the excessive harmonic frequency is reversed and superimposed on the power supply voltage control instruction, and the output voltage is controlled.

[0015] In a possible design, the single-phase grounding fault identification method specifically includes:

[0016] S201. Sampling phase current and zero-sequence current: the phase current and zero-sequence current of the three phases ABC on the power supply side of the distribution network are ia(k), ib(k), ic(k), i0(k), respectively, where k represents the current sampling period;

[0017] S202. Calculate the sampling change: Calculate the sampling change of the phase current and zero-sequence current of the three phases ABC according to the following formula, where Δia(k) represents the sampling change of the phase current of phase A, Δib(k) represents the sampling change of the phase current of phase B, Δic(k) represents the sampling change of the phase current of phase C, Δi0(k) represents the sampling change of the zero-sequence current, and k represents the current sampling period.

[0018]

[0019] S203. Calculate the error cycle sum: Calculate the error cycle sum between the phase current and the zero-sequence current of the three phases ABC according to the following formula, where N represents the number of sampling points in each power frequency cycle, Xa0 represents the error cycle sum between the phase current and the zero-sequence current of phase A, Xb0 represents the error cycle sum between the phase current and the zero-sequence current of phase B, Xc0 represents the error cycle sum between the phase current and the zero-sequence current of phase C, k represents the current sampling period,

[0020]

[0021] S204. Calculate the sum of squares of the cycle errors: Calculate the sum of squares of the cycle errors of the phase currents and the zero-sequence currents of the three phases ABC according to the following formula, where N represents the number of sampling points in each power frequency cycle, XXa represents the sum of squares of the cycle errors of the phase currents of phase A, XXb represents the sum of squares of the cycle errors of the phase currents of phase B, XXc represents the sum of squares of the cycle errors of the phase currents of phase C, XX0 represents the sum of squares of the cycle errors of the zero-sequence current, and k represents the current sampling cycle.

[0022]

[0023] S205. Calculate similarity: Calculate the similarity coefficients of the phase currents and the zero-sequence currents of the three phases ABC according to the following formula, where Pa0 represents the similarity coefficient between the A phase and the zero-sequence current, Pb0 represents the similarity coefficient between the B phase and the zero-sequence current, and Pc0 represents the similarity coefficient between the C phase and the zero-sequence current.

[0024]

[0025] S206. Determine the occurrence of a single-phase grounding fault and the faulty phase: When only one of the similarity coefficients Pa0, Pb0 and Pc0 calculated in S205 is greater than the set threshold, it is considered that a single-phase grounding fault has occurred, and the phase corresponding to the similarity coefficient greater than the set threshold is the faulty phase.

[0026] The present invention also provides a coordinated control system for power distribution network faults in a neutral point low-resistance grounding system, which is used in a single-power supply operation network powered by a high-voltage power electronic power supply, and includes a voltage oscillation and harmonic over-limit control unit and a single-phase grounding fault identification unit;

[0027] Wherein, the voltage oscillation and harmonic excess control unit is used to implement the steps of the above-mentioned voltage oscillation and harmonic excess control method when executing a computer program;

[0028] The single-phase grounding fault identification unit is used to implement the steps of the above-mentioned single-phase grounding fault identification method when executing a computer program.

[0029] The present invention mainly has the following beneficial effects:

[0030] (1) The present invention adopts a method for controlling voltage oscillation and harmonic excess, and can control the output voltage when voltage oscillation and harmonics occur during the operation of a distribution network of a neutral point low-resistance grounding system, thereby improving operation stability and safety;

[0031] (2) The present invention adopts the above-mentioned single-phase grounding fault identification method, and can determine the single-phase grounding fault and the faulty phase through the high similarity between the phase current and the zero-sequence current, thereby improving the accuracy of determination and identification. In particular, it can identify which phase has a grounding fault, greatly improving the efficiency of fault detection and reducing the difficulty of fault finding. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a flow chart of a method for controlling voltage oscillation and excessive harmonics in a coordinated control method for faults in a power distribution network of a neutral point low-resistance grounding system according to the present invention;

[0033] Figure 2 It is a flow chart of a single-phase grounding fault identification method in a coordinated control method for a power distribution network fault in a neutral point low-resistance grounding system of the present invention;

[0034] Figure 3 It is a structural schematic diagram of the method for coordinated control of power distribution network faults in a neutral point low-resistance grounding system of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, 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.

[0036] like Figure 1 As shown in the embodiment of the present invention, the coordinated control method for distribution network faults in a neutral point low-resistance grounding system is used in a single-power supply operation network powered by a high-voltage power electronic power supply, including a voltage oscillation and harmonic excess control method and a single-phase grounding fault identification method.

[0037] Among them, the voltage oscillation and harmonic excess control method cuts off the power supply and network connection when the power supply voltage of the distribution network oscillates, and performs the magnitude calculation of each harmonic distribution and harmonic frequency when the power supply voltage of the distribution network does not oscillate, and reverses and superimposes the harmonic frequency exceeding the standard on the power supply voltage control instruction to control the output voltage; Figure 1 As shown, specifically including:

[0038] Step S101: Collect the power supply voltage of the power distribution network.

[0039] Step S102. Voltage oscillation judgment: judge whether the system has voltage oscillation based on the collected distribution network power supply voltage (the method for judging the occurrence of voltage oscillation is an existing method, belongs to the prior art, and will not be described in detail here). If oscillation occurs, cut off the power supply and network connection (the specific control action can be tripping); if no oscillation occurs, execute S103.

[0040] Step S103. Calculate harmonic components: perform harmonic distribution and harmonic frequency calculations on the collected distribution network power supply voltage to obtain harmonic components; there are many methods for said calculations, such as Fourier analysis, instantaneous reactive power method, phase detection method, etc. These methods can all calculate harmonics and will not be described in detail here.

[0041] Step S104. Screening out excessive harmonic frequency signals: judging whether the harmonic components obtained in S103 exceed the set power quality standard (national standard GBT 14549-1993 "Power Quality Public Grid Harmonics", which stipulates the value that the harmonic components at each frequency cannot exceed), and executing S105 for the harmonic frequencies that exceed the set power quality standard.

[0042] Step S105. Superimpose harmonic frequency signal: compare the excessive harmonic frequency screened by S104 with the control and sampling frequency of the power supply. When 10 times the excessive harmonic frequency is less than or equal to the control and sampling frequency of the power supply (when fs≥10*fh, fs is the control and sampling frequency of the power supply, and fh is the harmonic frequency exceeding the standard obtained after calculation and comparison by S103 and S104), the signal of the excessive harmonic frequency is reversed (i.e., the sign is reversed), superimposed (i.e., added) to the power supply voltage control instruction, and the output voltage control is performed.

[0043] The voltage oscillation and harmonic excess control method can control the output voltage when voltage oscillation and harmonics occur during the operation of the distribution network of the neutral point low-resistance grounding system, thereby improving the operation stability and safety.

[0044] The single-phase grounding fault identification method calculates the current error frequency sum between the phase current and the zero-sequence current of each phase and the frequency sum of the phase current and the zero-sequence current of each phase according to the change in the phase current and the zero-sequence current of each phase on the power supply side of the distribution network, and then calculates the similarity between the phase current and the zero-sequence current of each phase to determine whether there is a single-phase grounding fault and the fault phase. Figure 2 As shown, specifically including:

[0045] Step S201. Sample phase current and zero-sequence current: the phase current and zero-sequence current of the three phases ABC on the power supply side of the distribution network are ia(k), ib(k), ic(k), i0(k), respectively, where k represents the current sampling period;

[0046] Step S202. Calculate the sampling change: Calculate the sampling change of the phase current and zero-sequence current of the three phases ABC according to the following formula, where Δia(k) represents the sampling change of the phase current of phase A, Δib(k) represents the sampling change of the phase current of phase B, Δic(k) represents the sampling change of the phase current of phase C, Δi0(k) represents the sampling change of the zero-sequence current, and k represents the current sampling period.

[0047]

[0048] Step S203. Calculate the error cycle sum: Calculate the error cycle sum between the phase current and the zero-sequence current of the three phases ABC according to the following formula, where N represents the number of sampling points in each power frequency cycle, Xa0 represents the error cycle sum between the phase current and the zero-sequence current of phase A, Xb0 represents the error cycle sum between the phase current and the zero-sequence current of phase B, Xc0 represents the error cycle sum between the phase current and the zero-sequence current of phase C, and k represents the current sampling period.

[0049]

[0050] Step S204. Calculate the sum of squares of the cycle errors: Calculate the sum of squares of the cycle errors of the phase currents and the zero-sequence currents of the three phases ABC according to the following formula, where N represents the number of sampling points in each power frequency cycle, XXa is the sum of squares of the cycle errors of the phase currents of phase A, XXb is the sum of squares of the cycle errors of the phase currents of phase B, XXc is the sum of squares of the cycle errors of the phase currents of phase C, XX0 is the sum of squares of the cycle errors of the zero-sequence current, k represents the current sampling cycle,

[0051]

[0052] Step S205. Calculate similarity: Calculate the similarity coefficients of the phase currents and the zero-sequence currents of the three phases ABC according to the following formula, where Pa0 represents the similarity coefficient between the A phase and the zero-sequence current, Pb0 represents the similarity coefficient between the B phase and the zero-sequence current, and Pc0 represents the similarity coefficient between the C phase and the zero-sequence current.

[0053]

[0054] Step S206. Determine whether a single-phase grounding fault and a faulty phase have occurred: when only one of the similarity coefficients Pa0, Pb0 and Pc0 calculated in S205 is greater than a set threshold, it is considered that a single-phase grounding fault has occurred, and the phase corresponding to the similarity coefficient greater than the set threshold is the faulty phase; wherein the threshold is an empirical value, which is 0.9.

[0055] The single-phase grounding fault identification method of the present invention adopts correlation determination, which is different from the traditional correlation method. The traditional correlation method is to determine the correlation between the phase currents of A, B, and C. When a single-phase grounding fault occurs, the fault phase has passed the grounding current, so the fault phase current must be different from the similar situation of the other two phases. This difference causes the phase current correlation to decrease, thereby reducing the accuracy of the single-phase grounding fault and the fault phase judgment; while the correlation determination of the single-phase grounding fault identification method of the present invention does not measure the correlation between the phase currents, but determines the correlation between the phase current and the zero-sequence current, because the phase current correlation is affected by harmonics and asymmetry, and the zero-sequence current is not affected by the arc suppression coil in the low-resistance grounding system, so the high similarity between the phase current and the zero-sequence current can be used to improve the accuracy of the single-phase grounding fault and the fault phase.

[0056] like Figure 3 As shown, the present invention also provides a coordinated control system for distribution network faults in a neutral point low-resistance grounding system, which is used in a single-power supply operation network powered by a high-voltage power electronic power supply, and includes a voltage oscillation and harmonic excess control unit 1 and a single-phase grounding fault identification unit 2. The voltage oscillation and harmonic excess control unit 1 is used to implement the steps of the above-mentioned voltage oscillation and harmonic excess control method when executing a computer program; the single-phase grounding fault identification unit 2 is used to implement the steps of the above-mentioned single-phase grounding fault identification method when executing a computer program.

[0057] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for coordinated control of power distribution network faults in a neutral point low resistance grounding system, characterized in that: The collaborative control method is used for a single-power supply operation network powered by a high-voltage power electronic power supply, including a voltage oscillation and harmonic excess control method and a single-phase ground fault identification method; The voltage oscillation and harmonic excess control method described herein cuts off the connection between the power supply and the network when the power supply voltage of the distribution network oscillates, and performs the magnitude calculation of the harmonic distribution and harmonic frequency when the power supply voltage of the distribution network does not oscillate, and reverses and superimposes the harmonic frequency exceeding the standard on the power supply voltage control instruction to control the output voltage; The single-phase grounding fault identification method calculates the current error frequency sum between the phase current and the zero-sequence current of each phase and the frequency sum of the phase current and the zero-sequence current of each phase according to the change of the phase current and the zero-sequence current of each phase on the power supply side of the distribution network, and then calculates the similarity between the phase current and the zero-sequence current of each phase to determine whether there is a single-phase grounding fault and the fault phase; The voltage oscillation and harmonic excess control method specifically includes: S101. Collecting power supply voltage of power distribution network; S102. Voltage oscillation judgment: determine whether the system has voltage oscillation according to the collected power supply voltage of the power distribution network. If oscillation occurs, cut off the power supply and network connection; if no oscillation occurs, execute S103; S103. Calculate harmonic components: perform harmonic distribution and harmonic frequency calculations on the collected power supply voltage of the distribution network to obtain harmonic components; S104. Screening excessive harmonic frequency signals: judging whether the harmonic components obtained in S103 exceed the requirements of the set power quality standard, and executing S105 for the harmonic frequencies exceeding the set power quality standard; S105. Superimpose harmonic frequency signal: compare the excessive harmonic frequency filtered by S104 with the control and sampling frequency of the power supply. When the 10 times excessive harmonic frequency is less than or equal to the control and sampling frequency of the power supply, the signal of the excessive harmonic frequency is reversed and superimposed on the power supply voltage control instruction, and the output voltage is controlled.

2. The collaborative control method according to claim 1, characterized in that: The single-phase grounding fault identification method specifically includes: S201. Sample phase current and zero-sequence current: The phase current and zero-sequence current of the three phases ABC on the power supply side of the distribution network are respectively , where k represents the current sampling period; S202. Calculate the sampling change: Calculate the sampling change of the phase current and zero-sequence current of the three phases ABC according to the following formula, where Indicates the sampling change of phase current of phase A, Indicates the sampling change of the phase current of phase B, Indicates the sampling change of the phase current of phase C, Indicates the sampling change of zero-sequence current, k indicates the current sampling period, S203. Calculate the error frequency sum: Calculate the error frequency sum between the phase current and the zero-sequence current of the three phases ABC according to the following formula: N Indicates the number of sampling points in each power frequency cycle, XA 0 represents the error frequency sum between the phase current of phase A and the zero-sequence current. Xb 0 represents the error frequency sum between the phase current of phase B and the zero-sequence current. XC 0 represents the error frequency sum between the phase current of phase C and the zero-sequence current. k Indicates the current sampling period. S204. Calculate the sum of squares of the frequency error: Calculate the sum of squares of the frequency error of the phase current and the zero-sequence current of the three phases ABC according to the following formula: N Indicates the number of sampling points in each power frequency cycle, XXa is the sum of squares of the phase current cycle error of phase A, XB is the sum of squares of the frequency error of the phase current of phase B, XX is the sum of squares of the cyclic error of the phase current of phase C, XX0 is the sum of squares of the zero-sequence current cycle errors, k Indicates the current sampling period. S205. Calculate similarity: Calculate the similarity coefficient between the phase current and the zero-sequence current of the three phases ABC according to the following formula: Pa 0 represents the similarity coefficient between phase A and zero-sequence current, Pb 0 represents the similarity coefficient between phase B and zero-sequence current, Pc 0 represents the similarity coefficient between phase C and zero-sequence current, S206. Determine the occurrence of a single-phase grounding fault and a faulty phase: When the similarity coefficient calculated in S205 Pa 0. Pb 0 and Pc 0 is greater than the set threshold, it is considered that a single-phase grounding fault has occurred, and the phase corresponding to the similarity coefficient greater than the set threshold is the fault phase.

3. A coordinated control system for power distribution network faults in a neutral point low resistance grounding system, characterized in that: The coordinated control system is used for a single-power supply operation network powered by a high-voltage power electronic power supply, and includes a voltage oscillation and harmonic excess control unit and a single-phase ground fault identification unit; Wherein, the voltage oscillation and harmonic excess control unit is used to implement the steps of the voltage oscillation and harmonic excess control method described in any one of claims 1-2 when executing a computer program; The single-phase grounding fault identification unit is used to implement the steps of the single-phase grounding fault identification method described in any one of claims 1-2 when executing a computer program.

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