Rail transit vehicle body current and vehicle body potential dynamic balance suppression method

Abstract

The application discloses a kind of car body current and car body potential dynamic balance inhibition method suitable for rail transit, using dynamic balance inhibition system includes current voltage acquisition module, main control module, impedance adjustment module;Current voltage acquisition module will be in each axle collected current signal and the voltage signal of each car body is transmitted to main control module;Main control module will signal be amplified, filtering, analog-digital conversion processing;Again, current voltage signal is substituted into the calculation formula including current, voltage average value and standard deviation with weight setting, and gives instruction after judging;Final instruction signal is then transmitted to impedance adjustment module from communication interface;Impedance adjustment module controls the on-off of capacitance and fixed resistance or adjusts the value of adjustable resistance according to instruction, realizes the goal of controlling car body current.The application realizes car body current and car body potential dynamic balance, improves the safety and stability of motor train unit.

Description

Technical Field

[0001] The present invention belongs to the technical field of rail transit grounding, and in particular relates to a method for suppressing the dynamic balance of vehicle body current and vehicle body potential applicable to rail transit. Background Art

[0002] Electrified rail transit trains integrate electrical, control, and communication equipment, and the onboard high- and low-voltage electrical equipment exhibit complex electrical characteristics and coupling relationships. The train grounding system is crucial for ensuring the discharge of traction and carbody currents. It primarily consists of two grounding methods: Working grounding connects the onboard traction transformer to the working ground wheel. The rolling electrical contact between the working ground wheel and the rails discharges the traction current, ultimately returning it to the ground traction substation via the rails, return lines, and integrated through-ground wires for energy recirculation. Second, protective grounding connects the carbody to the protective ground wheel, providing a common reference ground for onboard electrical equipment and ensuring the safety of passengers and onboard high- and low-voltage equipment. The proper configuration of the train's working ground and carbody protective grounding directly impacts the electromagnetic operating environment of the train's onboard equipment. During high-speed train travel, the "catenary-carbody-ground grounding system" forms a dynamically coupled return current system. The impedance of the "catenary-carbody" and "carbody-ground grounding systems" changes dynamically with the relative motion between the train and the rails. The rails serve as a common power return path, and both the working grounding wheel and the protective grounding wheel are in contact with them. This may cause the current released by the working grounding wheel to flow back to the car through the other protective grounding wheels, forming a "car-track" circulation. As the train runs dynamically, the impedance transient changes of the "contact network-car body" and "car body-ground grounding system" cause the circulation path and amplitude to change dynamically, ultimately resulting in long-term dynamically changing current on the car body.

[0003] During dynamic train operation, the grounding system provides a return path for the traction system's main circuit through working grounding. Protective grounding ensures equal potential between the car body and the track, preventing interference from numerous low-voltage devices that rely on the car body as a reference ground. Under certain special operating conditions, such as during pantograph raising and lowering, or when operating circuit breakers, high-frequency transient overvoltages can occur on the EMU car body. Protective grounding, the sole channel for discharging high-frequency transient voltages from the car body to the ground, ultimately discharges these voltages to the rails and the ground through the protective grounding. Consequently, protective grounding significantly impacts the propagation and distribution of overvoltages within the EMU car body. As EMU speeds continue to increase, numerous grounding-related issues have emerged. Experience has shown that, under normal operating conditions, improper grounding can lead to problems such as excessive circulating currents within the car body, electrical corrosion of bearings, and abnormal wear of carbon brushes. Under special transient conditions, improper grounding can cause excessively high car body potentials and even burn out speed sensors.

[0004] Furthermore, trains face special operating conditions during dynamic operation, such as over-sucking, over-phase separation, and over-insulation joints. These conditions can dramatically alter the train's ground return circuit topology, leading to dynamic impedance changes. High-speed railway traction networks employ suction lines and choke transformers approximately every 1.5 km. The choke transformers electrically connect two sections of track, with a suction line extending from the center of the choke transformer. This line shares the traction return current in the rails, routing it back to the traction substation via the suction line and a return line running parallel to the catenary. Since the EMU is a mobile load, it constantly approaches, passes through, and moves away from the suction line during operation. On the one hand, excessive protective grounding current will make the electromagnetic environment of the EMU worse, and interfere with the normal operation of weak current equipment such as communication and control of the EMU; on the other hand, when the protective grounding currents are unevenly distributed, some grounding carbon brushes will be severely worn and need to be replaced frequently, while the remaining carbon brushes with smaller grounding current do not need to be replaced frequently. However, since the carbon brushes are installed in the grounding device, it is difficult to directly judge the wear of each carbon brush. It is necessary to optimize the protective grounding, fully consider the maximum grounding current that occurs during the EMU's over-suction process, suppress excessive protective grounding current, and improve the uniformity of protective grounding current distribution.

[0005] During a train's phase-splitting process, the electrical parameters of the train, the catenary, and the neutral section continuously change as the train's relative position changes. These changes inevitably lead to sudden changes in voltage and current in the train's high-voltage system, generating overvoltages. During normal operation, a train frequently passes through electrical phase-splitting devices in different phase sections. Furthermore, as train speeds continue to increase, EMUs pass through electrical phase-splitting devices on the line more frequently. From the train's perspective, the system rapidly transitions from one state to another, causing changes in the circuit topology. For example, when a train transitions from the powered section to the neutral section and vice versa, the oscillations generated by the train passing through the neutral section can be superimposed on the overvoltages when power is restored, potentially significantly increasing the overvoltage amplitude. When a train passes through a phase-splitting process, the rooftop circuit breaker is in the open state, so the overvoltages caused by the phase-splitting overvoltage are primarily concentrated on the high-voltage equipment between the pantograph and the circuit breaker. The parasitic inductance of the grounding resistor significantly affects vehicle body overvoltages. However, for a fixed grounding resistor value, its parasitic inductance is difficult to change. Therefore, other methods can be used to reduce vehicle body overvoltage, such as utilizing the characteristics of capacitors that pass high frequencies and block low frequencies, and connecting capacitors in parallel next to the grounding resistor to suppress vehicle body overvoltage.

[0006] Analysis of the impact of grounding parameters on the performance of EMU mobile grounding systems reveals that increasing the grounding resistance suppresses the shaft-end grounding current amplitude, but also increases the body overvoltage amplitude. Reducing the grounding resistance reduces the body overvoltage, but also increases the grounding current. Therefore, when comprehensively optimizing the grounding system's performance, it is necessary to consider both the body current and the body potential amplitude. Current transformers and voltage transformers are used to enable online monitoring of the body current and body potential. After processing the current and voltage signals, the optimal resistance value is determined by considering their weighted ratio through an optimization algorithm. Therefore, given the characteristics and existing problems of current EMU grounding, it is necessary to systematically study EMU protective grounding and design a dynamic "body current-body potential" balance suppression method suitable for rail transit. Summary of the Invention

[0007] In response to the problems of ground current and car body overvoltage during train operation, the present invention provides a method for dynamically balancing car body current and car body potential applicable to rail transit.

[0008] The present invention provides a method for suppressing the dynamic balance of vehicle body current and vehicle body potential applicable to rail transit, and the "vehicle body current-vehicle body potential" dynamic balance suppression system used includes a current and voltage acquisition module, a main control module, and an impedance adjustment module.

[0009] The current and voltage acquisition module includes an on-board current transformer and an on-board voltage transformer, which transmits the current signal collected at each axis and the voltage signal of each vehicle body to the main control module.

[0010] The main control module includes a main control chip, a signal processing chip, a memory, a JTAG joint test download port, a power interface, and a communication interface; the signal is input from the communication interface to the signal processing chip through a transmission line, and the signal processing chip amplifies, filters, and performs analog-to-digital conversion on the signal; the main control chip substitutes the current and voltage signals into a calculation formula with set weights that includes the average value and standard deviation of current and voltage, and gives instructions after judgment; the final instruction signal is then transmitted from the communication interface to the impedance adjustment module; after the main control chip processes the signal, the result will be displayed in real time on the human-computer interaction interface, and the operator's instructions can also be imported into the main control module.

[0011] The impedance adjustment module includes a set of fixed resistors, an adjustable resistor and a capacitor. The fixed resistors are connected in parallel, then in series with the adjustable resistor, and then in parallel with the capacitor. The impedance adjustment module controls the on and off of the capacitor and the fixed resistor or adjusts the value of the adjustable resistor according to instructions to achieve the goal of controlling the vehicle current.

[0012] First, a power-on self-test is performed, and each hardware module of the system undergoes a safety test. After no abnormalities are detected, the system enters the ready state. After all hardware modules have been tested, the system starts working. Select the working condition (including over-suction line, over-phase, pantograph raising and lowering, and VCB operation) on the human-machine interface to enter different control modes:

[0013] For transient overvoltages under special operating conditions (over-phase, pantograph lifting and lowering, and VCB operation), a capacitor is selected to be connected in parallel.

[0014] For steady-state conditions under special operating conditions (over-absorption upper line), the on-board current transformer and voltage transformer monitor the vehicle body current and potential in real time. The collected signals are input into the main control module through the transmission line. The main control module amplifies, filters, and performs A / D conversion on the signals. The output signal is compared with the theoretical threshold value under the current operating conditions in the form of a digital quantity. If the limit is exceeded, the optimization algorithm is used to calculate the resistance value △R of the adjustable resistor, and the actuator controls the adjustable resistor to adjust the resistance value.

[0015] Repeat the above process after the system is powered on and self-tested to achieve dynamic balance between the actual voltage and the actual current.

[0016] The beneficial technical effects of the present invention are:

[0017] 1. Adjustable resistors and capacitors are introduced on the basis of the original grounding device. Different working conditions and control modes are selected through the human-machine interface, which increases the adaptability of the system. The system can also monitor the vehicle body potential and current, process the obtained voltage and current signals, and control the impedance adjustment module in real time to keep the current and voltage within the expected value range.

[0018] 2. The present invention aims at the dynamic process of train operation. The changing trends of the vehicle body voltage and ground current are different under different working conditions. The impedance adjustment module sets different optimization parameters according to the relationship between current and voltage under different working conditions; and through program control, it can directly adjust the resistance to the corresponding resistance value, avoiding the continuity and instability of the traditional electric sliding resistor in the resistance change, greatly shortening the adjustment time and improving the accuracy.

[0019] 3. When using a bus for communication, a serial communication protocol is employed, effectively preventing data transmission errors caused by interference during transmission. This method also offers excellent scalability, allowing multiple slave devices to communicate on the bus. The modular design is well-regulated, and each module has a mature data processing design, resulting in excellent system performance. The memory retains data after a power outage, and each system restart retains the previous memory, allowing the entire system to continuously optimize itself during operation, continuously improving the accuracy and speed of resistor adjustment.

[0020] 4. The system takes into comprehensive consideration the body current and body potential, overcoming the problem that when the grounding impedance is too high, although the body current is well suppressed, the body potential is difficult to discharge due to the high impedance. It effectively suppresses the grounding return during train operation, reduces the body potential, and makes the voltage and current distribution uniform; solves the problems of abnormal wear and insulation breakdown caused by large grounding return peak and poor uniformity, and at the same time suppresses the maximum overvoltage of the body, thereby improving the safety and stability of the EMU. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the "vehicle-track-network" return flow of rail transit.

[0022] Figure 2 This is a schematic diagram of the train passing through the suction line.

[0023] Figure 3 This is a schematic diagram of the train passing phase.

[0024] Figure 4 The flowchart of the “vehicle body current-vehicle body potential” dynamic balance suppression method.

[0025] Figure 5 This is a schematic diagram of the control system structure.

[0026] Explanation of Figure Symbols:

[0027] 1—catenary, 2—pantograph, 3—vacuum circuit breaker, 4—traction transformer, 5—traction motor, 6—traction converter, 7—rail, 8—protective grounding wheelset, 9—working grounding wheelset, 10—car body circulating current, 11—bogie, 12—return line, 13—suction line, 14—rail resistor Z1, 15—rail resistor Z2, 16—impedance adjustment module, 17—voltage transformer, 18—current transformer, 19—fixed resistor R1, 20—fixed resistor R2, 21—fixed resistor Rn , 22—adjustable resistor, 23—capacitor, 24—Phase A power supply station, 25—Phase B power supply station, 26—Phase A and B electrical phase separation area, 27—Phase A contact line, 28—Neutral line, 29—Phase B contact line, 30—Base, 31—Insulating support, 32—Arcing chamber, 33—JTAG joint test download port, 34—Main control chip, 35—Signal processing chip, 36—Communication interface, 37—Memory, 38—RESET button, 39—Switch, 40—Human-computer interaction interface, 41—Power supply. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0029] like Figure 1As shown, the high-speed train obtains high-voltage AC power from the contact network 1 through the pantograph 2 to drive the train. The current passes through the vacuum circuit breaker 3 and flows into the traction transformer 4. After passing through the traction converter 6, it provides power to the traction motor 5 that drives the train. The protective grounding wheel group 8 and the working grounding wheel group 9 are both connected to the rail 7. The rail 7 is both a reference ground for maintaining the ground potential of the vehicle body and a traction return path. Under normal operating conditions, the current on the rail will flow into the vehicle body through the protective grounding, forming a vehicle body circulation 10 and causing the vehicle body potential to fluctuate. When the over-absorption is on the line, as shown in FIG. Figure 2 As shown in FIG. 1 , a high-speed railway contact network 1 is provided with a suction line 12 every approximately 1.5 km to connect the rail 7 to the return line 12 transversely. Since the EMU is a mobile load, it constantly experiences the process of approaching, passing through, and moving away from the suction line during operation, resulting in dynamic changes in the rail resistance Z1 (14) and Z2 (15) at the left and right ends of the train. Therefore, the relative positions and electrical relationships between the EMU, the suction line, and the rails must be considered to fully reflect the changing characteristics of the ground return current under the EMU's operating state.

[0030] For transient overvoltages caused by special working conditions, such as when a train passes through phase separation, Figure 3 As shown. The neutral line 28 electrically separates the two-phase power supply arms A (27) and B (29) to avoid inter-phase short circuit. When the EMU enters the phase separation area, the vacuum circuit breaker 3 is disconnected, cutting off the main circuit to prevent overvoltage from invading the EMU main circuit and damaging the equipment during the phase separation process. However, when the on-board main circuit breaker is operated, the circuit topology changes, and the energy storage elements in the circuit are charged and discharged, causing circuit oscillation and generating car body overvoltage. Taking advantage of the characteristics of capacitors that pass high frequencies and block low frequencies, car body overvoltage can be suppressed by connecting a capacitor in parallel next to the grounding resistor.

[0031] The specific process and system structure of the method for suppressing the dynamic balance of vehicle body current and vehicle body potential applicable to rail transportation of the present invention are as follows: Figure 4 and Figure 5As shown. After the main control system is powered on, press the switch 39. First, the system is initialized and each module performs a self-check. If an unexpected situation occurs, press the reset button RESET38. The current CPU operation data can be cleared and started without powering off. Then, different working conditions are selected in the human-computer interaction interface 40: under working conditions such as over-phase, VCB operation, and bow lifting, the circuit topology changes cause the energy storage element to charge and discharge. The characteristics of the capacitor passing high frequencies and blocking low frequencies are utilized. By connecting a capacitor in parallel next to the grounding resistor, the circuit oscillation is suppressed to generate vehicle body overvoltage. When the over-absorption is on, the current transformer 18 and the voltage transformer 17 monitor the grounding current and vehicle body overvoltage in real time, and send them to the main control system through the communication interface 36. The system amplifies, filters, and performs analog-to-digital (A / D) conversion on the current and voltage signals. The output digital signal is compared with the preset threshold. If it is lower than the threshold, no adjustment is required. Otherwise, the resistance of the adjustable resistor is adjusted through the optimization algorithm. The selection of the current and voltage numerical weights in the algorithm is as follows:

[0032] The first is the objective function used to evaluate the grounding current, as shown in formula (a). It is mainly used to suppress the amplitude of each protective grounding current and reduce the imbalance of the protective grounding current as much as possible. Since the current amplitude problem has a greater impact, the average value of the grounding current peak value takes a larger weight in the grounding current objective function, and the overall standard deviation of the grounding current takes a smaller weight.

[0033]

[0034] Where, I ij ——The peak value of the ground current flowing through the j-axis of vehicle i, in A. Imean Indicates the average value of protective grounding current, f Istand Indicates the standard deviation of the protective earth current.

[0035] The second is the objective function used to evaluate the vehicle body potential, which is mainly to reduce the maximum voltage amplitude of each vehicle body as much as possible to prevent the train body potential from exceeding the safety limit of 2V, as shown in formula (b).

[0036]

[0037] Where U maxi —The maximum value of the vehicle body potential, in V. Umean Indicates the average value of the protective grounding voltage, f Ustand Indicates the standard deviation of the protective earth voltage.

[0038] Finally, considering the two sub-goals comprehensively, the objective function D is set as shown in formula (c).

[0039] D=ω1f I +ω2f U (c)

[0040] where ω1is the ground current weight ratio; and ω2is the car body voltage weight ratio.

[0041] However, the ground current objective function and the car body overvoltage objective function are not in the same order of magnitude. In order to make the objective function meaningful, they need to be normalized. The normalized objective function is shown in equation (d):

[0042] D g = ω1f I / 36.46 + ω2f U / 0.86 (d).

Claims

1. A method for suppressing the dynamic balance of vehicle body current and vehicle body potential applicable to rail transportation, characterized in that: The "vehicle body current-vehicle body potential" dynamic balance suppression system used includes a current and voltage acquisition module, a main control module, and an impedance adjustment module (16); The current and voltage acquisition module includes an on-board current transformer (18) and an on-board voltage transformer (17), and transmits the current signal collected from each axis and the voltage signal of each vehicle body to the main control module; The main control module includes a main control chip (34), a signal processing chip (35), a memory (37), a JTAG joint test download port (33), a power supply interface (41), and a communication interface (36); the signal is input into the signal processing chip (35) from the communication interface (36) through a transmission line, and the signal processing chip (35) amplifies, filters, and performs analog-to-digital conversion on the signal; the main control chip (34) substitutes the current and voltage signals into a calculation formula containing the average value and standard deviation of the current and voltage with set weights, and gives an instruction after judgment; the final instruction signal is then transmitted from the communication interface (36) to the impedance adjustment module (16); after the main control chip (34) processes the signal, the result will be displayed in real time on the human-computer interaction interface (40), and the operator's instruction can also be imported into the main control module; The impedance adjustment module (16) includes a set of fixed resistors (19-21), an adjustable resistor (22) and a capacitor (23). The fixed resistors (19-21) are connected in parallel, then connected in series with the adjustable resistor (22), and then connected in parallel with the capacitor (23). The impedance adjustment module (16) controls the on / off of the capacitor (23) and the fixed resistors (19-21) or adjusts the value of the adjustable resistor (22) according to instructions to achieve the goal of controlling the vehicle body current. The suppression method is specifically: First, a power-on self-test is performed, and each hardware module of the system undergoes a safety test. After no abnormalities are detected, the system enters the ready state. After all hardware modules have been tested, the system starts working. The working condition is selected on the human-computer interaction interface (40) to enter different control modes: For transient overvoltage under special working conditions, a capacitor (23) is selected in parallel; In view of the steady-state situation under special working conditions, the vehicle body current and vehicle body potential are monitored in real time by the on-board current transformer (18) and the on-board voltage transformer (17). The collected signals are input to the main control module through the transmission line. The main control module amplifies, filters, and performs A / D conversion processing on the signals. The output signal is compared with the theoretical threshold value under the current working condition in the form of digital quantity. If the limit is exceeded, the resistance value △R of the adjustable resistor (22) is calculated by the optimization algorithm, and the actuator controls the adjustable resistor (22) to adjust the resistance value. Repeat the above process after the system is powered on and self-tested to achieve dynamic balance between the actual voltage and the actual current.

2. A method for suppressing the dynamic balance of vehicle body current and vehicle body potential applicable to rail transit according to claim 1, characterized in that: The special operating conditions include over-suction upper line, over-phase, pantograph raising and lowering, and VCB operation.

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