Locomotive power battery electric quantity hysteresis equalization control method

Abstract

The invention relates to the field of locomotive power battery electric quantity control, and particularly discloses a locomotive power battery electric quantity hysteresis equalization control method, which comprises the following steps that: a traction force exerting mode is reset into an axle load transfer mode, and the initial value of an electric quantity equalization compensation coefficient K is a rack axle load transfer coefficient corresponding to zero speed; judging whether the current mode is a power battery power supply mode; if yes, the TCU receives the electric quantity of a front power battery and the electric quantity of a rear power battery in real time according to the current locomotive working mode, calculates the electric quantity average value difference value, monitors the auxiliary load power and the traction motor power and calculates the power difference value; entering a hysteresis control logic process; calculating a dynamic traction force compensation coefficient, ensuring that the traction force compensation amount is matched with the actual load characteristic of the system, correcting the traction characteristic curve in real time, and dynamically compensating the electric quantity difference of the battery; and performing traction distribution control according to the locomotive speed and outputting corresponding traction.

Description

Technical Field

[0001] The present invention relates to the field of locomotive power battery power control, and in particular to a locomotive power battery power hysteresis balancing control based on traction inverter power modulation. Background Art

[0002] In the field of rail transit, new energy locomotives, represented by the FXD3H shunting locomotive in the Fuxing series, adopt a new type of pantograph-power battery hybrid power supply mode, which combines the stability of grid power supply and the flexibility of power battery power supply, and is suitable for continuous operation in areas without pantograph coverage (such as tunnels, station shunting, etc.). However, due to the long-term difference in power requirements of the two auxiliary loads (such as air conditioners, fans, control systems, etc.) in front and behind the locomotive, the power battery is prone to SOC (charge) imbalance during frequent charging and discharging. Specifically, the battery discharge rate at the high-load end is faster, while the battery at the low-load end may be in a shallow charge and discharge state for a long time, resulting in inconsistent capacity attenuation between battery packs and shortening the overall life. Existing balancing control technology usually uses an auxiliary redundant contactor between the two busbars to achieve balancing by switching the auxiliary load consumption of the battery charge difference. It is difficult to apply to all working conditions in the face of complex and extreme operating conditions of the locomotive.

[0003] In order to ensure the consistency of discharge power of the two power battery packs and the continuous operation stability of the auxiliary load, and further improve the locomotive operation efficiency and the service life of the power switching devices, it is necessary to add power battery power balancing control to the traction inverter control strategy for real-time and effective balancing.

[0004] Prior art methods for controlling the discharge balance of locomotive traction batteries utilize two sets of power batteries for power supply. Two busbars, each carrying two traction loads, a constant-voltage and constant-frequency auxiliary load, and a variable-voltage and variable-frequency auxiliary load, are used. Both loads can be redundantly switched between the different busbars via four sets of contactors. Essentially, the locomotive compares the SOC consumption of the two power batteries and autonomously pairs the traction and auxiliary loads with the front-end battery via the CCU (network control unit), thereby compensating for power discrepancies caused by extended range. However, these methods suffer from the following drawbacks: First, the redundant contactors are not suitable for SOC balance control and shorten their lifespan. The essential function of the redundant contactors between the two busbars in the locomotive converter system is to prevent the shutdown of essential auxiliary loads (such as fans and water pumps) due to power loss to the entire converter system caused by a failure in a front-end power battery branch or DC / DC converter. Using these contactors for battery SOC balance control inevitably conflicts with locomotive-related load failures. While prioritizing normal operation, this can result in switching failures and failure to achieve power balance. Furthermore, the increased switching frequency of the contactors objectively shortens their service life. Secondly, when the battery charge difference reaches a certain threshold, the entire vehicle traction and auxiliary systems need to be shut down and restarted to complete the load switching, making it impossible to achieve real-time SOC balancing control. Under specific working conditions, such as when the locomotive runs on a long slope for a long time, the traction inverter cannot be shut down to switch the contactor to avoid driving risks. Secondly, there is the non-smooth switching between different traction modes of the locomotive: when the battery charge difference fluctuates near the threshold, the locomotive traction frequently switches between the original traction characteristics (including axle load transfer compensation) mode and the charge balancing mode, which can easily lead to sudden changes in traction and locomotive idling problems. Finally, the balancing effect is poor due to the lack of autonomous adjustment function of the load power: the power difference of the power batteries is caused by the accumulation of the load power difference over a long period of time. The two load powers are not adaptively adjusted according to the charge difference, but only compensated by switching the loads, making it difficult to quickly reach the charge compensation target value. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention discloses a method for controlling the hysteresis loop balance of the power battery of a locomotive, which specifically includes the following steps:

[0006] When the traction control unit is powered on, the locomotive control parameters are initialized, the traction force mode is reset to the axle load transfer mode, and the initial value of the power balancing compensation coefficient K is the axle load transfer coefficient Awk corresponding to zero speed. Based on the power battery pack input status, it is determined whether the current power supply mode is the power battery mode;

[0007] If yes, the traction control unit receives the power of the two power batteries in front and behind in real time according to the current locomotive operating mode, calculates the difference in the average power value, and monitors the auxiliary load power and traction motor power and calculates the power difference;

[0008] Entering the hysteresis control logic process: When the average battery value difference ΔSOC ≤ 1%, the axle load transfer mode is used to distribute the traction force of the front and rear frames. When ΔSOC ≥ 3%, it switches to the balanced mode to adjust the traction force. The frame with a high battery value increases ΔF, and the frame with a low battery value decreases ΔF. When 1% < ΔSOC < 3%, the current mode is maintained to avoid frequent switching of traction force caused by small fluctuations in the battery value difference.

[0009] Calculate the dynamic traction compensation coefficient: Set the power balance compensation coefficient The auxiliary load power difference ΔP and the total traction motor power P motor Dynamic association ensures that the traction force compensation matches the actual load characteristics of the system, then the compensation traction force ΔF = K × F, real-time correction of the traction characteristic curve and dynamic compensation for battery power differences;

[0010] Control traction force distribution according to locomotive speed and output corresponding traction force;

[0011] If the current power battery is not in the power supply mode, it will directly enter the axle load transfer control, continue to calculate the dynamic traction compensation coefficient and finally complete the traction distribution.

[0012] Furthermore, when traction force distribution control is performed according to locomotive speed:

[0013] During the starting phase, when the locomotive speed is ≤3km / h, the axle load transfer curve is mandatory to prioritize wheel-rail adhesion utilization during the starting phase and suppress idling;

[0014] In the transition phase, when the locomotive speed is less than 3 km / h and less than 6 km / h, the traction coefficient linearly transitions from the axle load transfer mode to the equilibrium mode;

[0015] During the balancing stage, when the locomotive speed is ≥6km / h, the battery balancing mode is fully enabled, and the battery balancing is performed using the traction redundancy method under high-speed conditions.

[0016] Furthermore, when the traction handle is at a high power demand level, it automatically switches to the axle load transfer mode to avoid the risk of idling under high traction; when a power battery branch or DC / DC fault is detected, the balancing control logic is immediately frozen and forced to return to the axle load transfer mode.

[0017] Furthermore, the locomotive control parameters include battery power difference ΔSOC, auxiliary load power difference ΔP, locomotive real-time speed, handle level and locomotive equipment status information, wherein the traction control unit first analyzes the locomotive control parameters and constructs a dynamic decision matrix to globally optimize the traction force distribution and simultaneously meet the power balance, operation stability and fault tolerance requirements.

[0018] Furthermore, when the locomotive is running at less than 3km / h, regardless of the value of the battery charge difference ΔSOC, the axle load transfer mode is forced to be adopted, and the traction force is distributed according to the preset curve; when the charging of the power battery pack is completed prematurely, the battery is not full and the initial battery charge difference ΔSOC = 2, it is between the two traction power mode thresholds. When the speed is greater than 3km / h, the battery hysteresis loop forces the use of the battery balancing mode, and the traction force is distributed according to the preset curve; when a battery branch fault is detected during operation, the traction inverter immediately stops the battery balancing logic and switches to the axle load transfer mode.

[0019] Due to the adoption of the above-mentioned technical solution, the present invention provides a locomotive power battery hysteresis balancing control method. This method realizes adaptive adjustment of traction force through power modulation of the traction inverter, combined with speed, handle level and fault status, to achieve dynamic balancing of the power of the front and rear power batteries, thereby solving the problem of unbalanced power of the two power battery packs in the actual use of the pantograph-grid-power battery hybrid power supply locomotive.

[0020] This method has been successfully applied to the traction inverter control of the Fuxing FXD3H locomotive. Since the initial operational evaluation phase of the Beijing Railway Bureau, the ΔSOC has been gradually optimized from 25 to around 5, achieving a nearly fivefold performance improvement, demonstrating excellent results. Currently, locomotives are mostly operating in shunting and limited operations. The optimization effect will be even more pronounced if the traction inverter is in long-term operation.

[0021] In addition, this method can smoothly switch traction modes and suppress idling and longitudinal impact: 1. Hysteresis control reduces switching frequency: By setting the hysteresis threshold of ΔSOC, frequent mode switching is avoided when the battery difference fluctuates. Application results show that compared with the traditional hard switching strategy, there is no problem of repeated mode switching, which can effectively prevent locomotive idling and longitudinal impulse caused by sudden changes in traction. 2. Dynamic adaptation of traction correction: Based on the linear proportional relationship of the compensation coefficient, the traction adjustment amount (ΔF) is matched with the load difference and motor power in real time to ensure a smooth correction process and improve the wheel-rail adhesion utilization rate by about 15%.

[0022] In addition, this method adaptively optimizes working conditions across the full speed range. When the speed is ≤3km / h: the axle load transfer curve is forcibly adopted, and the idling rate at the start-up stage is reduced by 30%-40%; 2. In the 3-6km / h transition section: the traction coefficient undergoes a linear transition, taking into account both anti-skid and balancing requirements, and the traction distribution error is controlled within ±2%; 3. At speeds ≥6km / h: the battery balancing mode is fully enabled, the battery charge difference (ΔSOC) converges, the speed is increased by 50%, and the balancing efficiency is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 Flow chart of the method of the present invention

[0025] Figure 2 This is a schematic diagram of the discharge of the power battery pack in the method of the present invention.

[0026] Figure 3 This is a flow chart of the hysteresis control logic process in the method of the present invention.

[0027] Figure 4 The logic diagram of the calculation process of the dynamic traction compensation coefficient in the method of the present invention is as follows:

[0028] Figure 5 Schematic diagram of the process of dynamically compensating battery power differences in the method of the present invention

[0029] Figure 6 Schematic diagram of the fault detection process in the method of the present invention DETAILED DESCRIPTION

[0030] To make the technical solutions and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention:

[0031] Taking the Fuxing FXD3H locomotive as an example, its electric drive system retains the common "AC-DC-AC" configuration used in electric locomotives. It consists of two bogies, each with a corresponding DC busbar. The front-end power supply of the DC busbar is a hybrid system of a power battery pack and a grid-connected traction four-quadrant rectifier. DC power at a specific voltage level charges the busbar support capacitors. The traction inverter and auxiliary inverter are connected to the positive and negative terminals of the busbar, converting it into three-phase AC power, which is then supplied to their respective downstream AC loads (traction motors, auxiliary fixed-frequency and variable-frequency loads). In pantograph-grid mode, the power battery pack is treated as a load and charged by the traction four-quadrant. In power battery mode, the power battery pack is charged only during braking conditions, when the traction motors provide feedback. The discharge of the power battery pack is entirely determined by the downstream DC / DC converter and the power level of the loads. The circuit block diagram is shown in Figure 2.

[0032] Because locomotives typically differentiate between auxiliary fixed-frequency loads and variable-frequency loads and connect them to two separate DC buses, this objectively leads to differences in the two auxiliary loads. Without any correction or compensation during long-term operation, the power battery pack's charge level (ΔSOC) can vary significantly.

[0033] To maintain adhesion control performance during locomotive operation when the locomotive speed is within the constant torque range, the traction inverter typically redistributes the traction forces among the individual locomotives according to the axle load transfer model, maintaining the same total traction power, to compensate for the traction power characteristics. Considering that in actual operating conditions, the locomotive is susceptible to idling due to the trailer load, often during the starting phase and when the traction handle is in a large position, the idling frequency decreases and eventually disappears as speed increases.

[0034] Therefore, this technical solution considers that in the power battery power supply mode, if the locomotive is in the non-starting stage and the traction handle is in a small position, the traction inverter can adaptively adjust the traction load power based on the original axle load transfer compensation mode to achieve the purpose of quickly balancing the battery power. Figure 1 A locomotive power battery hysteresis balance control method is shown, specifically including the following methods:

[0035] S1: Control parameter initialization and power supply mode determination:

[0036] S11: When the TCU is powered on, the control parameters are initialized, the traction force mode is reset to the axle load transfer mode, and the initial value of the power balance compensation coefficient K is the axle load transfer coefficient of the frame corresponding to zero speed.

[0037] S12: Determine whether the current mode is the power battery power supply mode according to the power battery pack input status.

[0038] S2: Real-time data collection and processing

[0039] S21: The TCU receives the power levels of the two power batteries (SOC_1 and SOC_2) in real time according to the current locomotive operating mode, calculates the average value difference ΔSOC = |(SOC_1-SOC_2) / 2|, and performs a limit operation.

[0040] S22: Monitor the auxiliary load power (P_aux1, P_aux2) and the traction motor power, and calculate ΔP = |P_aux1-P_aux2|.

[0041] S3: Multi-mode smooth switching mechanism based on hysteresis threshold, such as Figure 3 shown.

[0042] S31: Introduce hysteresis control logic (when ΔSOC ≤ 1%, the axle load transfer mode is used to distribute the traction of the front and rear frames; when ΔSOC ≥ 3%, it switches to the balancing mode to adjust the traction; the frame with high battery power increases ΔF, and the frame with low battery power decreases ΔF), and maintain the current mode within the threshold range (1% < ΔSOC < 3%) to avoid frequent switching of traction caused by small fluctuations in the battery power difference.

[0043] S32: Through the hysteresis interval design, "soft switching" between axle load transfer compensation mode and power balancing mode is achieved, and the mode switching is completed within 400ms of traction force, significantly reducing the risk of sudden changes in traction force and locomotive idling.

[0044] S4: Calculate the dynamic traction compensation coefficient, such as Figure 4 Shown: Proposed power balancing compensation coefficient Dynamically link the auxiliary load power difference (ΔP) with the total traction motor power (Pmotor) to ensure that the traction force compensation matches the actual load characteristics of the system; the compensated traction force ΔF = K×F is used to correct the traction characteristic curve in real time to achieve accurate dynamic compensation for battery power differences.

[0045] S5: Entering the traction force distribution stage based on speed classification, such as Figure 5 As shown:

[0046] S51: Starting phase (locomotive speed ≤ 3km / h): The axle load transfer curve is compulsorily adopted to prioritize wheel-rail adhesion utilization during the starting phase and suppress idling.

[0047] S52: Transition stage (3km / h < locomotive speed < 6km / h): The traction coefficient transitions linearly from the axle load transfer mode to the balance mode, taking into account low-speed safety and power balance requirements.

[0048] S53: Balancing stage (locomotive speed ≥ 6km / h): fully enable the battery balancing mode and use the traction redundancy of high-speed working conditions to achieve efficient battery balancing.

[0049] S6: Enter the intelligent emergency logic control process of the handle level and fault scenario:

[0050] S61: High-level mandatory protection: When the traction handle is in the high-power demand level, it automatically switches to the axle load transfer mode to avoid the risk of idling under high traction.

[0051] S62: Fast fault response: When a power battery branch or DC / DC fault is detected, the balancing control logic is immediately frozen and forced to fall back to the axle load transfer mode.

[0052] S7: Entering the collaborative control process of integrating multiple parameters:

[0053] S71: Integrate multi-dimensional parameters such as battery charge difference (ΔSOC), auxiliary load power difference (ΔP), real-time speed, handle level and device status to build a dynamic decision matrix.

[0054] S72: Global optimization of traction force distribution, while meeting the requirements of power balance, operational stability and fault tolerance.

[0055] S8: When a special situation occurs in the locomotive, the following protection is performed, such as Figure 6 As shown:

[0056] S81: When the locomotive is running below 3 km / h, regardless of the ΔSOC value, the axle load transfer mode is forced to be used, and the traction force is distributed according to the preset curve;

[0057] S82: The power battery pack is charged prematurely, the battery is not fully charged, and the initial ΔSOC = 2. The vehicle is between the thresholds of the two traction power modes. When the speed is greater than 3 km / h, the battery hysteresis loop forces the vehicle to adopt the battery balancing mode, and the traction force is distributed according to the preset curve.

[0058] S83: If a battery branch fault is detected during operation, the traction inverter immediately stops the battery balancing logic and switches to axle load transfer mode.

[0059] Furthermore, the method disclosed in this invention can extend battery life and optimize the battery's operating process, reducing capacity decay differences through dynamic balancing. By compensating for traction in real time, the difference in depth of discharge between the front and rear batteries is minimized, slowing overall battery capacity decay and extending service life. Through collaborative energy efficiency management, the auxiliary load power difference (ΔP) is factored into the calculation based on the compensation coefficient K, avoiding redundant energy loss and improving overall system energy efficiency by 8% to 10%.

[0060] Furthermore, this method can perform fault emergency response and improve system robustness. When the fault is quickly isolated and switched: when a battery branch or DC / DC fault is detected, the system freezes the balancing logic within 400μs and switches to the axle load transfer mode, reducing the traction force fluctuation amplitude by 30% under fault conditions; by forcing mode switching, the spread of the fault impact is avoided. Application results show that the mean time between failures (MTBF) of the traction inverter is extended to more than 2000 hours.

[0061] Furthermore, this method supports dynamic adjustment of key parameters, such as the hysteresis threshold (1%-3%) and speed segmentation points (3km / h, 6km / h), to adapt to different line conditions and vehicle model requirements. This method is implemented through TCU software upgrades, eliminating the need for new hardware and reducing deployment costs by over 90%. Therefore, this method can reduce the risk of traction loss of control and the accident rate, ensuring the safety of rail transit operations. Balanced control reduces the frequency of battery pack replacements, thereby reducing the waste of batteries such as lithium iron phosphate and lithium carbonate.

[0062] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A locomotive power battery hysteresis balance control method, characterized in that include: When the traction control unit is powered on, the locomotive control parameters are initialized, the traction force mode is reset to the axle load transfer mode, and the initial value of the power balancing compensation coefficient K is the axle load transfer coefficient Awk corresponding to zero speed. Based on the power battery pack input status, it is determined whether the current power supply mode is the power battery mode; If yes, the traction control unit receives the power of the two power batteries in front and behind in real time according to the current locomotive operating mode, calculates the difference in the average power value, and monitors the auxiliary load power and traction motor power and calculates the power difference; Entering the hysteresis control logic process: When the average battery value difference ΔSOC ≤ 1%, the axle load transfer mode is used to distribute the traction force of the front and rear frames. When ΔSOC ≥ 3%, it switches to the balanced mode to adjust the traction force. The frame with a high battery value increases ΔF, and the frame with a low battery value decreases ΔF. When 1% < ΔSOC < 3%, the current mode is maintained to avoid frequent switching of traction force caused by small fluctuations in the battery value difference. Calculate the dynamic traction compensation coefficient: Set the power balance compensation coefficient The auxiliary load power difference ΔP and the total traction motor power P motor Dynamic association ensures that the traction force compensation matches the actual load characteristics of the system, then the compensation traction force ΔF = K × F, real-time correction of the traction characteristic curve and dynamic compensation for battery power differences; Control traction force distribution according to locomotive speed and output corresponding traction force; If the current power battery is not in the power supply mode, it will directly enter the axle load transfer control, continue to calculate the dynamic traction compensation coefficient and finally complete the traction distribution.

2. The locomotive power battery hysteresis balance control method according to claim 1, characterized in that: When traction force distribution control is performed according to locomotive speed: During the starting phase, when the locomotive speed is ≤3km / h, the axle load transfer curve is mandatory to prioritize wheel-rail adhesion utilization during the starting phase and suppress idling; In the transition phase, when the locomotive speed is less than 3 km / h and less than 6 km / h, the traction coefficient linearly transitions from the axle load transfer mode to the equilibrium mode; During the balancing stage, when the locomotive speed is ≥6km / h, the battery balancing mode is fully enabled, and the battery balancing is performed using the traction redundancy method under high-speed conditions.

3. The locomotive power battery hysteresis balance control method according to claim 1, characterized in that: When the traction handle is at a high power demand level, it automatically switches to the axle load transfer mode to avoid the risk of idling under high traction force; when a power battery branch or DC / DC fault is detected, the balancing control logic is immediately frozen and forced to return to the axle load transfer mode.

4. The locomotive power battery hysteresis balance control method according to claim 1, characterized in that: The locomotive control parameters include the battery charge difference ΔSOC, the auxiliary load power difference ΔP, the locomotive real-time speed, the handle level and the locomotive equipment status information. The traction control unit first analyzes the locomotive control parameters and constructs a dynamic decision matrix to globally optimize the traction force distribution while meeting the requirements of power balance, operation stability and fault tolerance.

5. The locomotive power battery hysteresis balance control method according to claim 1, characterized in that: When the locomotive runs at a speed lower than 3km / h, the axle load transfer mode is forced to be adopted regardless of the battery charge difference ΔSOC value, and the traction force is distributed according to the preset curve; when the power battery pack charging is completed prematurely, the battery is not full and the initial battery charge difference ΔSOC = 2, it is between the two traction power mode thresholds. When the speed is greater than 3km / h, the battery hysteresis loop forces the use of the battery balancing mode, and the traction force is distributed according to the preset curve; when a battery branch fault is detected during operation, the traction inverter immediately stops the battery balancing logic and switches to the axle load transfer mode.

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