A feeder protection method for a flexible DC traction power supply system

Abstract

The present invention discloses a feeder protection method for a flexible DC traction power supply system. The line reactor and DC support capacitor in the main circuit of the locomotive traction inverter in the flexible DC traction power supply system are used as boundary elements. The feeder current is collected based on the 4-20mA current loop of the unilateral traction station to perform fault judgment. The feeder protection start-up constant, delay time constant and protection action constant are set by calculating the transient quantity of the identification criterion and the direction criterion, thereby realizing ultra-high-speed identification of small short-circuit current faults and locomotive start-up in the flexible DC traction power supply system. Compared with the prior art, the present invention optimizes the protection method implementation process, and is simple to implement, highly adaptable, low in investment, economically friendly, and has a strong ability to resist transition resistance.

Description

Technical Field

[0001] The invention belongs to the field of relay protection of flexible DC traction power supply systems in urban rail transit, and in particular relates to a feeder protection method for a flexible DC traction power supply system. Background Art

[0002] Feeder protection of flexible DC traction power supply system is crucial to the safe and reliable operation of flexible DC traction power supply system. Rapid and reliable identification of DC side faults is one of the key technologies for the development of flexible DC traction power supply system, and it is also a key link in the green and intelligent integration development of urban rail flexible DC traction power supply system. Feeder protection is mainly used to identify short-circuit faults in DC traction network, quickly isolate faults within a small time window after the fault occurs, and avoid the phenomenon of large fault current impacting important power supply equipment in DC traction substation, such as damaging converters, traction networks, DC fast circuit breakers, power supply cables, etc. Traditional ROR (rate of raise) protection based on current change rate di / dt and current increment ΔI can realize fault identification by judging the current change rate di / dt, current increment ΔI and delay, but it has the problems of low speed and sensitivity for the identification of small and medium short-circuit current faults. In the traditional DC traction power supply system based on uncontrolled rectification, when a small short-circuit current fault occurs in the traction network, the current change rate di / dt and current increment ΔI of the fault current may be less than or equal to the locomotive starting current, resulting in a long delay for the ROR protection to realize fault identification and thus remove the fault. This situation is a major safety hazard and poses a severe challenge to the reliability of the system.

[0003] Since the DC side of the bidirectional converter of the flexible DC traction power supply system is equipped with a large DC support capacitor, when a fault occurs in the DC traction network, the DC support capacitor discharges quickly, which makes the fault characteristics of the flexible DC traction power supply system and the traditional DC traction power supply system very different. At the same time, as the departure time interval of urban rail transit locomotives is getting shorter and shorter, the locomotive load is getting heavier, so the locomotive start-up, especially the simultaneous start-up current of multiple vehicles, is very similar to the current of small short-circuit current fault, and there is a risk of false operation or refusal of ROR protection. This puts forward new requirements for the speed and sensitivity of the feeder protection of the flexible DC traction power supply system, and it is necessary to study the new principle of feeder protection of the flexible DC traction power supply system to ensure the safe and reliable power supply of the system. Summary of the invention

[0004] In view of this, in order to solve the problems of slow identification speed, low accuracy, and easy false operation and refusal to operate of the existing ROR protection in the flexible DC traction power supply system for small short-circuit current faults and simultaneous starting of multiple vehicles, the present invention proposes a feeder protection method for a flexible DC traction power supply system, which calculates the transient quantity identification criterion and direction criterion, sets the feeder protection starting constant, delay time constant and protection action constant, and aims to achieve ultra-high-speed identification of small short-circuit current faults and locomotive starting in the flexible DC traction power supply system.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A feeder protection method for a flexible DC traction power supply system, which uses the line reactor and DC support capacitor in the main circuit of the locomotive traction inverter in the flexible DC traction power supply system as boundary elements, collects the feeder current based on the 4-20mA current loop of the unilateral traction station, calculates the identification criterion and the direction criterion, sets the feeder protection starting value, delay time value and protection action value according to the identification criterion and direction criterion of the transient quantity, and performs the traction network short-circuit current fault judgment and locomotive starting current identification of the flexible DC traction power supply system; the specific steps are as follows:

[0007] The process of collecting feeder current based on the 4-20mA current loop of the single-side traction station specifically includes the following processing:

[0008] S21, establish a 4-20mA current loop to provide feeder current analog data to the DC protection device feeder current acquisition and control system;

[0009] S22, initializing the DC protection device feeder current collection and control system, including, in sequence, initializing the FPGA phase-locked loop PLL to generate a sampling clock clk0, initializing the sampling interval t0, initializing the sampling interrupt int0, and initializing the sampling buffers buf0 and buf1;

[0010] S23, the feeder current collection control system obtains the sampling interval t0 according to the rising edge count of clk0 set in the sensitive list, samples periodically according to the sampling interval t0, and caches the sampling results in the two sampling buffers buf0 or buf1;

[0011] S24, the feeder current collection and control system sends an interrupt instruction int0 to the CPU at the end of the sampling interval t0, and the CPU responds to the interrupt instruction int0 and reads the feeder current sampling data from the two buffers buf0 or buf1 in a time-sharing manner;

[0012] S25, repeat steps S23 to S25;

[0013] The process of calculating the amount identification criterion and the direction criterion specifically includes the following processing:

[0014] S31, after the CPU reads the feeder current sampling data in time-sharing, according to the feeder protection task beat, after accumulating t1 time, the calculation data window is obtained, and the data in the calculation data window is decomposed into wavelet components of different scales by wavelet transform to obtain the wavelet coefficients C of each component. j (k); where j represents the decomposition scale of the feeder current and k represents the time domain position of the coefficient in the calculation data window;

[0015] S32, calculate the increase vector ΔI of the feeder current, ΔI is used as the direction criterion, and the direction criterion threshold ΔI is set th ;

[0016] S33, calculate the wavelet energy entropy E of the feeder current s , as shown below:

[0017]

[0018] E s As the identification criterion, set the identification criterion threshold E sth ;

[0019] S34, if the current increment ΔI<ΔI th , it is determined to be a reverse interval disturbance, then the current feeder protection process is exited and returned to S31; if ΔI>ΔI th , it is determined to be a forward interval disturbance, and further judgment is needed E s With E sth , to identify whether the forward section is a traction network short-circuit fault or a locomotive start, where ΔI represents the current increment, ΔI th Indicates the current increment threshold;

[0020] S35, if E s <E sth , it is determined that the locomotive is started and it is a normal load current, then the current feeder protection process is exited and returned to S31; if E s >E sth , it is determined that there is a short-circuit fault in the traction network in the forward section, the feeder protection is activated, and the output is tripped;

[0021] According to the identification criteria and direction criteria of transient quantities, the starting setting, delay time setting and protection action setting of the feeder protection are set to perform small short-circuit current fault judgment of the traction network of the flexible DC traction power supply system and locomotive starting current identification.

[0022] The 4-20mA current loop includes a DC feeder, a shunt, a DC current transmitter, a DC protection device, a DC bus and a high-speed circuit breaker HSCB, the high-speed circuit breaker is connected to the shunt, the shunt is connected to the DC feeder, the DC feeder is connected to the DC traction network, the shunt is connected to the DC current transmitter, and the DC current transmitter is connected to the DC protection device.

[0023] The starting setting value of the set feeder protection is the setting value at which the protection device detects and triggers the corresponding protection action when a fault or locomotive starts; the delay time setting value of the set feeder protection is the setting value at which the corresponding protection action is triggered after the delay time after the protection device detects the fault or locomotive starts to avoid false operation of the protection; the action setting value of the set feeder protection is the threshold required to determine the protection device to trigger the protection action.

[0024] Compared with the prior art, the feeder protection method of a flexible DC traction power supply system described in the present invention can achieve the following beneficial technical effects:

[0025] The protection method implementation process has been optimized to achieve ultra-high-speed identification of small short-circuit current faults and locomotive start-up in the flexible DC traction power supply system. The protection principle is simple, adaptable, requires low investment, and is economically friendly. It also has a strong ability to tolerate transition resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of an embodiment of a high-frequency component path of a small short-circuit current fault and locomotive startup of a flexible DC traction power supply system of the present invention;

[0027] Figure 2 A schematic diagram of an implementation path of a method for protecting feeder lines of a flexible DC traction power supply system according to the present invention;

[0028] Figure 3 It is a state flow chart of collecting feeder current in a 4-20mA current loop of a DC protection device of a flexible DC traction power supply system of the present invention;

[0029] Figure 4 It is a fault judgment flow chart of the present invention;

[0030] Reference numerals:

[0031] 1. High-frequency component path of small short-circuit current fault, 2. High-frequency component path of locomotive starting current, 3. Contact rail, 4. Rail. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0033] The invention discloses a feeder protection method for a flexible DC traction power supply system. Firstly, a 4-20mA current loop of a DC protection device of the flexible DC traction power supply system is used to collect feeder current. By using a time-varying non-stationary signal time-frequency analysis tool, feeder current characteristic quantities are calculated and extracted. Then, transient quantity identification criteria and direction criteria are calculated. Feeder protection starting constants, delay time constants and protection action constants are set, thereby realizing ultra-high-speed identification of small short-circuit current faults in the traction network of the flexible DC traction power supply system and locomotive starting current. Compared with the prior art, the present invention uses the line reactor and DC support capacitor in the main circuit of the locomotive traction inverter of the flexible DC traction power supply system as boundary elements, and utilizes the boundary characteristics of the boundary elements that block the high-frequency components of the locomotive starting current. By using the time-varying non-stationary signal time-frequency analysis tool to extract characteristic quantities, reliable and ultra-high-speed identification of small short-circuit current faults in the traction network is achieved. This method collects feeder current data through a 4-20mA current loop for single-sided traction for fault identification, does not rely on communication, and has a novel and efficient acquisition and control method. The protection principle is simple to implement, has strong adaptability, and is economical, and has a strong ability to resist transition resistance.

[0034] like Figure 1 As shown, the high-frequency component path of the small short-circuit current fault of the flexible DC traction power supply system in the prior art and the high-frequency component path of the locomotive starting current are listed respectively. For the locomotive starting situation, since the three-phase asynchronous motor IM will generate a large amount of high-frequency components when starting and transmit them from the traction inverter to the traction network, but there are boundary elements in the main circuit of the traction inverter, namely the line reactor FL and the DC support capacitor FC, and the boundary elements have a strong blocking boundary characteristic for the high-frequency components of the locomotive starting current, then after propagating through the traction network, the high-frequency transient energy entropy detected by the DC protection devices M and N installed in the flexible DC traction stations A and B is small. On the contrary, if a small short-circuit current fault occurs, due to the absence of boundary elements, a large amount of high-frequency components propagate to the DC protection devices M and N of the flexible DC traction stations A and B, and then the high-frequency transient energy entropy detected by M and N is large. Therefore, a time-varying non-stationary signal time-frequency analysis tool is used to extract high-frequency feature quantities, that is, wavelet transform is used to extract the difference in high-frequency feature quantities of the locomotive starting current and the small short-circuit current fault current, so as to realize the ultra-high-speed identification of the small short-circuit current fault and the locomotive starting current of the flexible DC traction power supply system.

[0035] like Figure 2 As shown, the DC protection device of the flexible DC traction power supply system collects feeder current through a 4-20mA current loop. The 4-20mA current loop includes a DC feeder, a shunt, a DC current transmitter, a DC protection device, a DC bus and a high-speed circuit breaker HSCB, the high-speed circuit breaker is connected to the shunt, the shunt is connected to the DC feeder, the DC feeder is connected, and the DC traction network is composed of Figure 1 The contact rail and the steel rail are composed of the shunt and the DC current transmitter, and the DC current transmitter is connected to the DC protection device to ensure the accuracy and reliability of the DC feeder current data collection.

[0036] Further, such as Figure 3 As shown, the specific steps of the DC protection device of the flexible DC traction power supply system collecting the feeder current through the 4-20mA current loop include:

[0037] S21, establish a 4-20mA current loop to provide feeder current analog data to the DC protection device feeder current acquisition and control system;

[0038] S22, initializing the DC protection device feeder current collection and control system, including, in sequence, initializing the FPGA phase-locked loop PLL to generate a sampling clock clk0, initializing the sampling interval t0, initializing the sampling interrupt int0, and initializing the sampling buffers buf0 and buf1;

[0039] S23, the feeder current collection control system obtains the sampling interval t0 according to the rising edge count of clk0 set in the sensitive list, samples periodically according to the sampling interval t0, and caches the sampling results in the two sampling buffers buf0 or buf1;

[0040] S24, the feeder current collection and control system sends an interrupt instruction int0 to the CPU at the end of the sampling interval t0, and the CPU responds to the interrupt instruction int0 and reads the feeder current sampling data from the two buffers buf0 or buf1 in a time-sharing manner;

[0041] S25. Repeat steps S23 to S25.

[0042] like Figure 4 As shown, a feeder protection method for a flexible DC traction power supply system of the present invention utilizes wavelet transform to extract feeder current characteristic quantities, obtains transient quantity identification criteria and direction criteria through calculation, sets feeder protection start-up constants, delay time constants and protection action constants, and thereby realizes ultra-high-speed identification of small short-circuit current faults and locomotive starting currents of the flexible DC traction power supply system.

[0043] The purpose of setting the feeder protection start-up setting value is to ensure that when a fault or locomotive start-up occurs, the protection device can detect and trigger the corresponding protection action in a timely and accurate manner. The specific steps of setting the feeder protection start-up setting value include:

[0044] SX1. System characteristics analysis: Conduct a comprehensive analysis of the characteristics of the flexible DC traction power supply system, including power supply voltage, locomotive load characteristics, system capacity and small current fault characteristics, and conduct steady-state and transient characteristics analysis of the system;

[0045] SX2, Fault simulation and emulation: Use electromagnetic transient simulation tools to simulate faults, simulate various fault conditions and locomotive startup scenarios, and record the corresponding current and voltage waveform data. Based on these data, the response and characteristics of the system under different conditions can be analyzed;

[0046] SX3, Standards and Specifications Reference: Refer to applicable national or industry standards and system equipment specifications, which may include recommendations or requirements for protection start settings. The standards and specifications usually provide guidelines and methods for setting protection devices;

[0047] SX4, retrieval expert system: refer to the DC traction power supply system protection setting expert system;

[0048] SX5. Field testing and verification: Field testing is performed to verify and optimize the protection start-up settings. By monitoring and recording the actual system operating data, including faults and locomotive start-up events, as well as the response and operation of the protection devices, corrections and adjustments are made based on the test results until the feeder protection start-up setting requirements are met.

[0049] The delay time setting of the feeder protection is to ensure that after the protection device detects a fault or the locomotive starts, the corresponding protection action can be triggered after an appropriate delay time to avoid false protection action; the selection of the delay time depends on the response speed of the system and the protection task target; the specific steps of setting the delay time setting of the feeder protection include:

[0050] SY1. Determine the target protection speed: First, calculate the system safety, fault impact and protection speed to determine the target protection speed under fault or locomotive start event conditions;

[0051] SY2. Analyze system response time: Analyze the detection time of the protection device, signal transmission time and operation time of the protection equipment, etc.

[0052] SY3. Classification of fault types and fault characteristics: Set different delay times according to different fault types and fault characteristics. For example, a transient fault only requires a short delay time or zero delay, while a permanent fault may require a longer delay time; adjust the delay time constant according to the duration and characteristics of the fault.

[0053] SY4. Retrieval expert system: refer to the DC traction power supply system protection setting expert system;

[0054] SY5. Balance the reliability and false operation rate of the protection system: avoid untimely protection response due to too long delay time, and too short delay time may cause false operation. Balance the reliability and false operation rate of the protection system and select the appropriate delay time;

[0055] SY6. Field testing and verification: Field testing is performed to verify and optimize the protection start settings by monitoring and recording the actual system operating data, including faults and locomotive start events, as well as the response and operation of the protection devices. Corrections and adjustments are made based on the test results until the feeder protection delay time setting requirements are met.

[0056] The purpose of setting the action value of the feeder protection is to determine the threshold or condition required for the protection device to trigger the protection action. The specific setting method and steps will vary depending on the different protection devices and applications. The specific steps of setting the action value of the protection include:

[0057] SZ1. Have an in-depth understanding of the system characteristics and operating conditions of the feeder protection, including locomotive load characteristics, short-circuit capacity, electrical parameters, etc., and determine the fault types and conditions that the protection device needs to detect and respond to through system analysis;

[0058] SZ2. Refer to applicable national or industry standards and system equipment specifications to ensure that the setting process complies with the requirements of standards and specifications, and implement the setting of action settings using the guiding principles and methods for setting the action settings of protection devices provided by standards or specifications;

[0059] SZ3, search the expert system to obtain the setting reference of the DC traction power supply system protection setting expert system;

[0060] SZ4. Conduct fault simulation and field testing to simulate the transient and steady-state characteristics under different fault types, record the response and action of the protection device, analyze the sensitivity and accuracy of the protection device based on the test results, and make appropriate adjustments and optimizations.

[0061] SZ5. Monitor and record actual operating data, that is, monitor and record the action of the protection device and the operating data of the system, and analyze these data to verify and optimize the action setting of the protection device.

[0062] SZ6. Reliability and safety verification: Verify the effectiveness and accuracy of the action setting according to the reliability and safety requirements of the system to ensure that the protection device can accurately detect and respond to faults while avoiding false operation and excessive false operation rate.

[0063] The specific steps of obtaining the identification criterion and the direction criterion by calculation include:

[0064] S31, after the CPU reads the feeder current sampling data in time-sharing, it is stored in DDR3. According to the feeder protection task beat, after accumulating t1 time, the calculation data window is obtained. The data in the calculation data window is decomposed into wavelet components of different scales by wavelet transform, and the wavelet coefficient C of each component is obtained. j (k); where j represents the decomposition scale of the feeder current and k represents the time domain position of the coefficient in the calculation data window;

[0065] S32, calculate the increase vector ΔI of the feeder current, ΔI is used as the direction criterion, and the direction criterion threshold ΔI is set th ;

[0066] S33, calculate the wavelet energy entropy E of the feeder current s , as shown below:

[0067]

[0068] E s As the identification criterion, set the identification criterion threshold E sth ;

[0069] S34, if the current increment ΔI<ΔI th , it is determined to be a reverse interval disturbance, then the current feeder protection process is exited and returned to S31; if ΔI>ΔI th , it is determined to be a forward interval disturbance, and further judgment is needed E s With E sth , to identify whether the forward section is a traction network short-circuit fault or a locomotive start, where ΔI represents the current increment, ΔI th Indicates the current increment threshold;

[0070] S35, if E s <E sth , it is determined that the locomotive is started and it is a normal load current, then the current feeder protection process is exited and returned to S31; if E s >E sth , it is determined that there is a short-circuit fault in the traction network in the forward section, the feeder protection is activated, and the output trips.

[0071] In summary, a feeder protection method for a flexible DC traction power supply system of the present invention uses the line reactor and DC support capacitor in the main circuit of the locomotive traction inverter in the flexible DC traction power supply system as boundary elements. The boundary elements have a strong blocking boundary characteristic for the high-frequency component of the locomotive starting current, but have no effect on the high-frequency component of the small short-circuit current fault current of the traction network. The difference in high-frequency characteristic quantities of the locomotive starting current and the small short-circuit current fault current is extracted by using wavelet transform. By calculating the wavelet energy entropy of the feeder current as a judgment condition, reliable and ultra-high-speed identification of small short-circuit current faults in the traction network can be achieved; at the same time, the feeder current increment vector is used as a directional element to effectively ensure the directionality of the protection and reduce the difficulty of setting the feeder protection constant; the feeder protection method has a fast action speed capability and can quickly identify a short-circuit fault after a traction network fault occurs;

[0072] In addition, the present invention collects feeder current data based on the 4-20mA current loop of a single-side traction station for fault identification, does not rely on two-end communication, and has a novel and efficient collection and control method, which optimizes the protection method implementation process. The protection principle is simple to implement, has strong adaptability, requires little investment, is economical, and has a strong ability to resist transition resistance.

[0073] The above description is only an embodiment of the present application and is not intended to limit the scope of protection to be applied for by the present invention. For those skilled in the art, any modification, equivalent substitution or variation made through various changes and variations without departing from the spirit and principle of the present invention shall fall within the technical content and protection scope disclosed by the present invention.

Claims

1. A feeder protection method for a flexible DC traction power supply system, characterized in that: The line reactor and DC support capacitor in the main circuit of the locomotive traction inverter in the flexible DC traction power supply system are used as boundary elements. The feeder current is collected based on the 4-20mA current loop of the traction station on one side, and the identification criterion and direction criterion are calculated. According to the identification criterion and direction criterion of the transient quantity, the feeder protection starting value, delay time value and protection action value are set to judge the small short-circuit current fault of the traction network of the flexible DC traction power supply system and identify the locomotive starting current. The specific steps are as follows: The process of collecting feeder current based on the 4-20mA current loop of the single-side traction station specifically includes the following processing: S21, establish a 4-20mA current loop for providing feeder current analog data to the DC protection device feeder current acquisition and control system; the 4-20mA current loop includes a DC feeder, a shunt, a DC current transmitter, a DC protection device, a DC bus and a high-speed circuit breaker HSCB, the high-speed circuit breaker is connected to the shunt, the shunt is connected to the DC feeder, the DC feeder is connected to the DC traction network, the shunt is connected to the DC current transmitter, and the DC current transmitter is connected to the DC protection device; S22, initializing the DC protection device feeder current collection and control system, including, in sequence, initializing the FPGA phase-locked loop PLL to generate a sampling clock clk0, initializing the sampling interval t0, initializing the sampling interrupt int0, and initializing the sampling buffers buf0 and buf1; S23, the feeder current collection and control system obtains the sampling interval t0 according to the rising edge count of clk0 set in the sensitive list, samples periodically according to the sampling interval t0, and caches the sampling results in the two sampling buffers buf0 or buf1; S24, the feeder current collection and control system sends an interrupt instruction int0 to the CPU at the end of the sampling interval t0, and the CPU responds to the interrupt instruction int0 and reads the feeder current sampling data from the two buffers buf0 or buf1 in a time-sharing manner; S25, repeat steps S23 to S25; The process of calculating the identification criterion and the direction criterion specifically includes the following processing: S31, after the CPU reads the feeder current sampling data in time-sharing, according to the feeder protection task beat, after accumulating t1 time, the calculation data window is obtained, and the data in the calculation data window is decomposed into wavelet components of different scales by wavelet transform to obtain the wavelet coefficients C of each component. j (k); where j represents the decomposition scale of the feeder current and k represents the time domain position of the coefficient in the calculation data window; S32, calculate the increase vector ΔI of the feeder current, ΔI is used as the direction criterion, and the direction criterion threshold ΔI is set th ; S33, calculate the wavelet energy entropy E of the feeder current s , as shown below: E s As the identification criterion, set the identification criterion threshold E sth ; S34, if the current increment ΔI<ΔI th , it is determined to be a reverse interval disturbance, then the current feeder protection process is exited and returned to S31; if ΔI>ΔI th , it is determined to be a forward interval disturbance, and further judgment is needed E s With E sth , to identify whether the forward section is a traction network short-circuit fault or a locomotive start, where ΔI represents the current increment, ΔI th Indicates the current increment threshold; S35, if E s <E sth , it is determined that the locomotive is started and it is a normal load current, then the current feeder protection process is exited and returned to S31; if E s >E sth , it is determined that there is a short-circuit fault in the traction network in the forward section, the feeder protection is activated, and the output is tripped; According to the identification criterion and direction criterion of the transient quantity, the starting setting value, delay time setting value and protection action setting value of the feeder protection are set to perform small short-circuit current fault judgment of the traction network of the flexible DC traction power supply system and locomotive starting current identification; the starting setting value of the set feeder protection is the setting value that the protection device detects and triggers the corresponding protection action when a fault or locomotive starts; the delay time setting value of the set feeder protection is the setting value that triggers the corresponding protection action after the delay time after the protection device detects the fault or the locomotive starts to avoid false operation of the protection; the action setting value of the set feeder protection is the threshold required to determine the protection device to trigger the protection action.

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