Vehicle-mounted energy storage system and control method based on vehicle-mounted energy storage system

Abstract

The invention discloses a vehicle-mounted energy storage system and a control method based on the vehicle-mounted energy storage system, and relates to the field of rail transit alternating current transmission control. Aiming at the improvement that a traditional low-frequency oscillation suppression scheme mostly focuses on power supply adjustment or network side control, the invention provides a vehicle-mounted energy storage system which can utilize an energy source outside a power grid to replace or share load power borne by the power grid. Under the light-load working condition, the vehicle-mounted energy storage system completely replaces a power grid to bear the load power of the train, at the moment, the train does not need to be powered by the power grid, harmonic coupling between the train and other trains does not exist, and inducements generated by low-frequency oscillation are fundamentally eliminated. In addition, under the heavy load working condition, the energy storage device can share a part of train load power, so that the power exchange strength between the train and the power grid is reduced, and the problem of low-frequency oscillation caused by mismatching between power supply of the power grid and the load is relieved.

Description

Technical Field

[0001] This application relates to the field of AC drive control for rail transit, and particularly to an on-vehicle energy storage system and a control method based on the on-vehicle energy storage system. Background Art

[0002] Low-frequency oscillation is a key technical problem in the actual operation of heavy-haul or high-speed trains. Due to its complex inducement factors, involving multiple interdisciplinary fields, the technical complexity is reflected in multiple aspects such as power electronics, control theory, electromechanical coupling, and system stability. And during the operation of the train, once low-frequency oscillation occurs, it will inevitably have a serious impact on the safety and operation order of the railway. Therefore, how to suppress low-frequency oscillation during train operation has always been the focus and difficulty that those skilled in the art have been concerned about.

[0003] Currently, the research on suppressing low-frequency oscillation mainly focuses on how to improve the power supply conditions or improve the performance from the grid-side control. While the application scenarios are limited, the suppression effect on low-frequency oscillation is also restricted by the grid side.

[0004] Therefore, those skilled in the art now urgently need an on-vehicle energy storage system to provide a new idea and solution for solving the problem of suppressing low-frequency oscillation. Summary of the Invention

[0005] The purpose of this application is to provide an on-vehicle energy storage system and a control method based on the on-vehicle energy storage system, which are used to solve the problem of low-frequency oscillation during train operation.

[0006] To solve the above technical problems, this application provides an on-vehicle energy storage system, including: an energy storage device, a DC converter, and a control device;

[0007] Wherein, the energy storage device is connected to the DC bus in the train traction system through the DC converter;

[0008] The DC converter is used to control the energy exchange between the energy storage device and the DC bus;

[0009] The control device is connected to the DC converter and is used for: if the train is in a light-load condition, controlling the energy storage device to independently supply power to the load of the train; if the train is in a non-light-load condition, when low-frequency oscillation occurs in the train, controlling the energy storage device to inject power support into the DC bus.

[0010] To solve the above technical problems, this application also provides a control method based on the on-vehicle energy storage system, which is applied to the on-vehicle energy storage system as described above. The method includes:

[0011] Obtain the current load condition of the train; wherein, the load condition includes: light-load condition and non-light-load condition;

[0012] If the load condition is a light load condition, control the four - quadrant converter in the train traction system to stop working, and control the DC - DC converter to make the energy storage device independently supply power to the load of the train;

[0013] If the load condition is a non - light load condition, when the train has low - frequency oscillation, control the DC - DC converter to make the energy storage device inject power support into the DC bus and jointly supply power to the load of the train with the power grid.

[0014] In a possible embodiment, the control of the DC - DC converter to make the energy storage device inject power support into the DC bus and jointly supply power to the load of the train with the power grid includes:

[0015] Taking the output target value of the energy storage device as the given quantity and the actual output value of the energy storage device as the feedback quantity, the DC - DC converter performs output control on the energy storage device through a closed - loop regulator;

[0016] Wherein, the output target value of the energy storage device is determined according to the total load power of the train.

[0017] In a possible embodiment, the method for determining the output target value of the energy storage device includes:

[0018] Obtain the average value of the total load power of the train;

[0019] Determine the output power target value of the energy storage device according to the product of the average value of the total load power and a preset suppression coefficient; wherein, the suppression coefficient is any positive number less than or equal to 1;

[0020] Determine the output target value of the energy storage device according to the output power target value.

[0021] In a possible embodiment, after taking the output target value of the energy storage device as the given quantity and the actual output value of the energy storage device as the feedback quantity, and the DC - DC converter performs output control on the energy storage device through a closed - loop regulator, it further includes:

[0022] Judge whether the low - frequency oscillation of the train still exists;

[0023] If so, increase the suppression coefficient to re - determine the output target value of the energy storage device, and return to the step of taking the output target value of the energy storage device as the given quantity and the actual output value of the energy storage device as the feedback quantity, and the DC - DC converter performs output control on the energy storage device through a closed - loop regulator.

[0024] In a possible embodiment, it further includes:

[0025] If there is still low-frequency oscillation in the train when the suppression coefficient increases to 1, gradually reduce the traction power of the train until the low-frequency oscillation of the train is eliminated.

[0026] In a possible embodiment, it further includes:

[0027] Obtain the instantaneous value of the DC voltage, and extract the instantaneous value of the secondary ripple from the instantaneous value of the DC voltage;

[0028] Determine the secondary ripple amplitude and the secondary ripple inverse proportional coefficient according to the instantaneous value of the secondary ripple; wherein, the secondary ripple inverse proportional coefficient is negatively correlated with the secondary ripple amplitude;

[0029] Control the output of the energy storage device through a secondary pulsation suppression strategy;

[0030] The secondary pulsation suppression strategy is a double closed-loop control strategy; wherein, the outer loop of the secondary pulsation suppression strategy is a negative feedback closed-loop control structure with the secondary ripple target given value as the outer loop given quantity and the secondary ripple amplitude as the feedback quantity; the inner loop of the secondary pulsation suppression strategy is a negative feedback closed-loop control structure with the product of the output of the outer loop and the secondary ripple inverse proportional coefficient as the inner loop given quantity and the actual output value of the energy storage device as the inner loop feedback quantity.

[0031] In a possible embodiment, determining the secondary ripple inverse proportional coefficient according to the instantaneous value of the secondary ripple includes:

[0032] Obtain the historical fluctuation range of the secondary ripple;

[0033] Determine the position of the first quantile of the instantaneous value of the secondary ripple in the historical fluctuation range of the secondary ripple;

[0034] Determine the position of the second quantile according to the complementary mapping of the position of the first quantile;

[0035] Based on the position of the second quantile, determine the corresponding value from the preset inverse proportional coefficient value range as the secondary ripple inverse proportional coefficient;

[0036] Wherein, the median of the inverse proportional coefficient value range is 1.

[0037] In a possible embodiment, it further includes:

[0038] Control the train to stop traction operation and enter the static pantograph-raising state;

[0039] Control the output of the energy storage device through the DC converter to establish the DC bus voltage, and control the four-quadrant converter to operate in the inverter mode to deliver capacitive reactive power to the power grid.

[0040] In a possible embodiment, it further includes:

[0041] Control the train to stop traction operation and enter the static pantograph-raising state;

[0042] Control the output of the energy storage device through the DC converter to establish the DC bus voltage, and control the four-quadrant converter to operate in the inverter mode to deliver capacitive reactive power or inductive reactive power to the power grid.

[0043] In a possible embodiment, the train is multiple;

[0044] Then the control of the four-quadrant converter to operate in the inverter mode to deliver capacitive reactive power or inductive reactive power to the power grid includes:

[0045] Control the first part of the train to deliver capacitive reactive power to the power grid and control the second part of the train to deliver inductive reactive power to the power grid;

[0046] Wherein, the sum of the capacitive reactive power delivered to the power grid by the first part of the train is equal to the sum of the inductive reactive power delivered to the power grid by the second part of the train.

[0047] In a possible embodiment, it further includes:

[0048] If there is still remaining capacity in the output power of the four-quadrant converter after bearing the load of the train, control the four-quadrant converter to output at the rated power and control the energy storage device to operate in the charging mode through the DC converter.

[0049] In a possible embodiment, it further includes:

[0050] If the traction motor in the train operates in the braking mode, control the traction inverter to operate in the braking state and control the energy storage device to operate in the charging mode through the DC converter.

[0051] In a possible embodiment, it further includes:

[0052] When the train passes through the neutral section, control the energy storage device to supply power to the load of the train through the DC converter.

[0053] In a possible embodiment, it further includes:

[0054] When the power grid loses power or the train runs in a non-electrified railway section, control the energy storage device to supply power to the load of the train through the DC converter.

[0055] In a possible embodiment, it further includes:

[0056] When the power grid cannot independently bear the load of the train, the energy storage device is controlled by the DC converter to inject power support into the DC bus, and jointly supply power to the load of the train with the power grid.

[0057] The on-vehicle energy storage system provided by this application adds an energy storage device and a DC converter for controlling its input / output in the train, so as to supply power to the DC bus of the train through the energy storage device when the train has low-frequency oscillations or is in a working condition prone to low-frequency oscillations. Among them, if the energy storage device can independently bear the power supply requirement of the train load, the operation of the four-quadrant converter can be stopped, that is, the energy storage device replaces the power grid to achieve the power supply of the train load. At this time, since the train does not require power supply from the power grid, the train does not need to connect to the grid, and there will be no coupling with other trains on the grid, thus avoiding the generation of low-frequency oscillations. When the energy storage device cannot independently bear the power supply requirement of the train load, the energy storage device and the power grid can jointly supply power to the train load. At this time, the energy storage device can replace the power grid to bear part of the train load power, so the energy obtained by the train from the power grid is reduced, and the power exchange intensity between the train and the power supply system is also reduced, and the low-frequency oscillations of the power grid will be quickly alleviated.

[0058] As can be seen from the above, this application provides a low-frequency oscillation suppression solution different from improving the power supply conditions or grid-side control performance, providing a new solution and idea for avoiding possible low-frequency oscillation problems during train operation. Moreover, the low-frequency oscillation suppression achieved based on this application can adapt to various train load working conditions and can obtain good suppression effects.

[0059] The control method based on the on-vehicle energy storage system provided by this application corresponds to the above on-vehicle energy storage system, and the effect is the same. Description of the Drawings

[0060] In order to more clearly illustrate the embodiments of this application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of this application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0061] Figure 1 It is a structural diagram of an on-vehicle energy storage system provided by the present invention;

[0062] Figure 2 It is a flowchart of a control method based on an on-vehicle energy storage system provided by the present invention;

[0063] Figure 3 It is a control block diagram of a low-frequency oscillation suppression solution provided by the present invention;

[0064] Figure 4 Flow chart of a low-frequency oscillation suppression solution provided by the present invention;

[0065] Figure 5 Control block diagram of a secondary pulsation suppression solution provided by the present invention. Specific implementation manners

[0066] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present application.

[0067] The core of the present application is to provide a vehicle-mounted energy storage system and a control method based on the vehicle-mounted energy storage system.

[0068] In order to enable those skilled in the art to better understand the solution of the present application, the present application will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0069] During the actual operation of an AC drive electric locomotive, various serious faults often occur due to vehicle-network coupling. Among them, the more typical ones are:

[0070] 1. In some old lines, there are often insufficient capacities in certain power supply sections, and there is a possibility that multiple trains operate under heavy load in this section due to scheduling reasons. At this time, due to the mismatch between power supply and load, violent power disturbances will occur in the power supply section. As a result, low-frequency oscillations of the grid voltage will be caused, leading to faults such as overcurrent and overvoltage in the substation or the train, seriously affecting the normal operation order of the railway.

[0071] 2. In the station yard, there are often many locomotives or multiple units parked in the same power supply section. At this time, although the trains are in a light load condition, due to the harmonic coupling between multiple trains, low-frequency oscillations of the grid will still be caused, and then large-area faults of the trains in the station yard will be triggered, resulting in serious accidents and seriously affecting the railway transportation order.

[0072] Based on the above, the present application summarizes two major causes of low-frequency oscillations that occur during the actual train operation: 1. Heavy load condition: mismatch between large load and grid power supply capacity; 2. Light load condition: harmonic coupling between multiple trains when multiple trains are powered by the grid at the same time.

[0073] To solve the above problems, the present application provides a vehicle-mounted energy storage system, as Figure 1 shown, including: an energy storage device, a DC converter, and a control device.

[0074] Among them, the energy storage device is connected to the DC bus in the train traction system through a DC converter; the DC converter is used to control the energy exchange between the energy storage device and the DC bus; the control device is connected to the DC converter and is used for: if the train is in a light load condition, controlling the energy storage device to independently supply power to the train load; if the train is in a non-light load condition, when the train has low-frequency oscillations, controlling the energy storage device to inject power support into the DC bus.

[0075] In the on-vehicle energy storage system provided above, the energy storage device can be a large-capacity electricity storage device such as a power battery, and its specifications and parameters should be determined according to the actual train traction power supply needs, and this embodiment does not limit this. The DC converter, as the energy conversion device of the energy storage device, is used to control the input and output of the energy storage device, and its specific model and specifications should be determined according to the control needs of the energy storage device.

[0076] It should be noted that the above control device can be an additional controller device such as a Digital Signal Processor (DSP) or a Microcontroller Unit (MCU) for specifically controlling the input or output of the energy storage device. In addition, the above control device can also reuse the control device of the original train electric traction system that controls various devices including the four-quadrant converter to integrate the input and output control of the newly added energy storage device into the train traction control, reducing the additional hardware cost and also being beneficial to ensuring that the energy storage device will not have an adverse impact on the normal traction control of the train. In this case, in addition to having a communication connection with the DC converter to ensure its control over the DC converter, the control device also has communication connections with devices such as the four-quadrant converter, traction inverter, and auxiliary inverter. Due to the uncertainty of the connection relationship of the control device in different implementation schemes, Figure 1 the control device and its connection relationship are not shown in the figure, but this does not mean Figure 1 that the above control device does not exist in the shown on-vehicle energy storage system, and this control device may be shared with the original train traction system.

[0077] In addition, as can be seen from the above, the on-vehicle energy storage system provided in this application is connected to the DC bus in the train traction system, which is equivalent to being connected in parallel with the power grid. When the power grid is powered and the four-quadrant converter is working properly, the energy storage device can either not work or supply power to the train load (such as Figure 1 the traction load and auxiliary load in the figure, Figure 1 the catenary in the figure is another name for the power grid) together with the power grid, and when the power grid has no power or the four-quadrant converter stops working, the energy storage device can also supply power to the train load instead of the power grid.

[0078] As can be seen from the cause 2 of low-frequency oscillation summarized in the above description, if the energy storage device can supply power to the train load instead of the power grid, the train does not need to connect to the grid, and there is no harmonic coupling between multiple trains, thus fundamentally solving the low-frequency oscillation problem.

[0079] Relatedly, when the train is in a light load condition such as parked inside the station yard, the current common control methods are as follows:

[0080] 1) Directly start the four-quadrant converter to bear all loads.

[0081] 2) Stop the four-quadrant converter and establish the intermediate DC voltage through diode rectification.

[0082] 3) First, put into the four-quadrant converter to establish a stable DC voltage; then put into a larger-capacity auxiliary load; then stop the four-quadrant converter and maintain the DC voltage and the auxiliary load through diode rectification.

[0083] Among them, the disadvantage of the above control method 1) is that due to the large number of trains in the station, a large number of AC trains run unloaded in the same power supply section, and it is easy to excite low-frequency oscillation due to the coupling relationship between them. The disadvantage of the above control method 2) is that the sudden input of a large-capacity load (such as an auxiliary load) will impact the DC circuit, and then the train is prone to report an undervoltage fault. Although the above control method 3) takes into account the advantages of the previous two methods, its disadvantage is that the logic timing is complex and the engineering application is relatively cumbersome.

[0084] However, the suppression of low-frequency oscillation when the train is in a light load condition realized by the on-vehicle energy storage system provided in this application does not have the problems existing in the three common control methods in the above related technologies. It can completely avoid the occurrence of low-frequency oscillation caused by multi-train resonance coupling; the sudden input of a large-capacity auxiliary load can also be fully tolerated without causing the train to report an undervoltage fault; at the same time, the motor power is small at this time, and it can also perform low-speed and low-power traction without starting the four-quadrant converter, which can reduce the mutual interference between the numerous AC trains in the station and is a very safe solution.

[0085] In addition, when the energy storage device independently powers the train load instead of the power grid, it generally occurs when the train load is small, that is, the train is in a light load condition. From the inducement 1 of low-frequency oscillation summarized in the above description, it can be seen that the application scenario targeted by inducement 1 is when the train load is large, that is, the train is in a light load condition. At this time, it is usually difficult for the energy storage device to replace the power grid to supply power to the train load. However, at this time, the DC converter can be used to control the energy storage device to share a part of the load power originally provided by the power grid. That is, by supplying power through the energy storage device, the energy obtained by the train from the power grid is reduced, and the power exchange intensity between the train and the power supply system is decreased. Based on this, from the principle derivation of the low-frequency oscillation generated by the above inducement 2, it can be seen that the low-frequency oscillation of the power grid will be alleviated at this time.

[0086] In addition, it should be noted that although the above embodiment describes how to suppress the low-frequency oscillation of the train in light load and heavy load conditions in the above description. In fact, the specific definition criteria for light load and heavy load are not restricted. As can be seen from the above, in the light load condition, the energy storage device completely replaces the power grid to bear the train load power. That is, it implies the condition that the total train load power is less than or equal to the maximum output power (rated power) of the energy storage device. Similarly, in the heavy load condition, it is difficult for the energy storage device to independently bear the total train load power. Therefore, the method of jointly bearing the total train load power with the power grid is selected to reduce the power exchange intensity between the train and the power grid, so as to alleviate the low-frequency oscillation of the power grid. That is, the heavy load condition implies the condition that the total train power load is greater than the maximum output power (rated power) of the energy storage device. Thus, it can be seen that for the light load condition and heavy load condition mentioned above in this embodiment, they can be defined based on the magnitude relationship between the total power required by the current load and the maximum output power of the energy storage device.

[0087] In addition, based on other requirements that may occur in practical applications, there may be other classification requirements for the train load condition in addition to the light load and heavy load conditions. At this time, no matter how many types the train load condition is split into, it can be distinguished by whether it is a light load condition. Among them, the working condition where the load power can be independently borne by the energy storage device is regarded as the above light load condition, and the rest of the working conditions are regarded as non-light load conditions, and the corresponding scheme under the above heavy load condition can be used to suppress the low-frequency oscillation.

[0088] In summary, based on the setting of the on-vehicle energy storage system, the present application can use an energy source outside the power grid to replace or share the load power borne by the power grid. Under light load conditions, the energy storage device in the on-vehicle energy storage system can completely replace the power grid to bear the train load power. At this time, the train does not need to connect to the grid, and there is no harmonic coupling with other trains, fundamentally solving the inducement of low-frequency oscillation. Under heavy load conditions, even if the energy storage device cannot completely replace the power grid to bear the train load power, it can also share a part of it, thereby reducing the power exchange intensity between the train and the power grid and alleviating the low-frequency oscillation problem caused by the mismatch between the power grid power supply and the load. It can be seen that the present system can provide corresponding low-frequency oscillation suppression solutions for two different inducements of train low-frequency oscillation, is applicable to light load, heavy load and other working conditions of the train, covers various situations that may occur in the actual operation of the train, is suitable for the new construction of electric locomotives or the transformation of old electric locomotives, greatly improves the availability of the train and the adaptability to the power grid, and enhances the reliability of railway transportation.

[0089] On the other hand, in the above embodiment, an on-vehicle energy storage system is described in detail. The on-vehicle energy storage system can replace or share the power grid to support the train load power, so as to achieve the effect of avoiding or alleviating low-frequency oscillation. Therefore, how to control the output of the energy storage device in the on-vehicle energy storage system becomes the key to suppressing low-frequency oscillation of the on-vehicle energy storage system. In view of this, the present application also provides a control method based on the on-vehicle energy storage system, which is applied to the on-vehicle energy storage system provided in the above embodiment. The method is as Figure 2 shown and includes:

[0090] S11: Obtain the current load condition of the train.

[0091] Among them, the load condition includes: light load condition and non-light load condition.

[0092] S12: If the load condition is a light load condition, control the four-quadrant converter in the train traction system to stop working, and control the DC converter to make the energy storage device independently supply power to the train load.

[0093] S13: If the load condition is a non-light load condition, when the train has low-frequency oscillation, control the DC converter to make the energy storage device input power support into the DC bus and supply power to the train load together with the power grid.

[0094] For step S11, as can be seen from the embodiments of the above vehicle-mounted energy storage system, the distinction between the light load condition and the non-light load condition here is only a simple distinction of the load condition for determining which low-frequency oscillation suppression scheme to adopt subsequently, and does not mean that the load conditions of the train in actual application only include these two types: the light load condition and the non-light load condition. In addition, for the definition of whether the load condition is a light load condition, it can be determined according to the maximum output power of the energy storage device. Of course, the load condition can also be distinguished based on other parameters. For example, in a possible implementation, this embodiment also provides another definition criterion for the light load condition: the train load power ≤ 10% of the single-motor power.

[0095] To demonstrate that this method does not limit the train to only having two operating conditions, light load and non-light load, in actual operation, referring to the above-provided definition criterion for the light load condition, this embodiment also provides two other possible load conditions and their definition criteria:

[0096] Medium load condition: 10% of the single-motor power < train load power ≤ 30% of the single-motor power.

[0097] Heavy load condition: train load power > 30% of the single-motor power.

[0098] And the medium load condition and the heavy load condition in this embodiment both belong to the above non-light load condition, and low-frequency oscillation suppression is performed through the control scheme corresponding to step S13.

[0099] In addition, for the identification of the above train load situation, it is necessary to obtain the load power (corresponding to Figure 1 , that is, the total power of the traction load and the auxiliary load). For the acquisition of the load power, this embodiment provides several possible implementation schemes:

[0100] S11-1: Obtain the load power of each load of the train from the load end and calculate the sum of the load powers.

[0101] Exemplarily, as Figure 1 shown, this step is also to separately obtain the motor power borne by the traction inverter in the train traction system and the auxiliary load power borne by the auxiliary inverter, and then obtain the total load power by calculating the sum of the motor power and the auxiliary load power.

[0102] S11-2: Identify the power at the load end through the method of load power observation.

[0103] The implementation carrier of this load acquisition method is generally in the controller of the four-quadrant converter. Since in the original train traction system, it is the four-quadrant converter (power grid) that bears all the loads of the train, the output power of the four-quadrant converter is also the total power required by the train load.

[0104] S11-3: Obtain the DC bus voltage value and the DC bus current value through the voltage sensor and current sensor installed in the intermediate DC circuit, and obtain the load power by multiplying the DC bus voltage value by the DC bus current value.

[0105] This solution is similar to the above solution S11-3. Based on the characteristic that the intermediate DC circuit undertakes the power supply for all loads, by obtaining the voltage and current on the intermediate DC circuit, the power on the intermediate DC circuit, that is, the total power at the load end, is directly calculated based on the power calculation formula.

[0106] It should be noted that the several load power acquisition and load condition identification solutions provided in the above embodiments are only a possible implementation solution. In actual applications, the load power can also be obtained through other means, and then it can be determined whether the current train load is in a light load condition or other conditions, so as to select a suitable low-frequency oscillation suppression solution.

[0107] After that, for steps S12 and S13, as described in the embodiments of the above vehicle-mounted energy storage system part, they are low-frequency oscillation suppression solutions for two different load conditions of the train. For example, for step S12, when the train is in a light load condition, the train load is small. At this time, the energy storage device can replace the power grid to undertake all the power required by the train load. That is, at this time, the four-quadrant converter can stop working, the train is disconnected from the grid, and the power grid does not need to supply power to the train. And because the train is disconnected from the grid, there will be no resonant coupling between trains, and thus no low-frequency oscillation will occur. Similarly, for step S13, when the train is in a non-light load condition, it is difficult for the energy storage device to undertake all the train load power alone, and the low-frequency oscillation suppression solution in step S12 is no longer applicable. At this time, as in step S13, a method of jointly supplying power by the power grid and the energy storage device can be adopted to provide necessary power support for the train load. At this time, compared with the original situation where the power grid alone undertakes all the train load power, the power exchange intensity between the power grid and the train can be reduced, thereby alleviating the low-frequency oscillation problem caused by the mismatch between the power grid power supply and the load.

[0108] It can be seen that a control method based on a vehicle-mounted energy storage system provided in this application can specifically solve the inducement of low-frequency oscillation problems when the train is in different load conditions through the vehicle-mounted energy storage system provided in the above embodiments. Thus, the effect of adapting to various conditions during the actual operation of the train and suppressing low-frequency oscillation can be achieved. And this method is a low-frequency oscillation suppression solution different from improving power supply regulation and improving control performance on the power grid side, providing new ideas and means for solving the train low-frequency oscillation problem.

[0109] On the other hand, as can be seen from the low-frequency oscillation suppression scheme corresponding to the above step S13, as long as the energy storage device shares a part of the load power for the power grid, a certain low-frequency oscillation suppression effect can be achieved. The amount of the output power of the energy storage device and the specific output control scheme adopted only differ in the quality of the suppression effect. In view of this, this embodiment also provides a further implementation scheme for step S13. The above step S13 specifically includes:

[0110] S131: Using the output target value of the energy storage device as the given quantity and the actual output value of the energy storage device as the feedback quantity, the DC converter controls the output of the energy storage device through a closed-loop regulator.

[0111] Among them, the output target value of the energy storage device is determined according to the total load power of the train.

[0112] In this embodiment, in order not to affect the normal traction load and auxiliary load, the DC bus voltage is still controlled by a four-quadrant converter. The DC converter controls the output of the energy storage device in a single control loop working mode, and its control block diagram is shown in Figure 3.

[0113] Specifically, the DC converter does not perform closed-loop control on the DC voltage, but only performs closed-loop control on the output quantity (output current or output power) of the energy storage device. In the closed-loop control, the feedback quantity is the actual value (i.e., the instantaneous value) of the output quantity of the energy storage device. In addition, the given value of the closed-loop control is the target value of the output quantity of the energy storage device (for example, the expected value of the output quantity corresponding to the energy storage device when it undertakes the planned load power it undertakes), and the difference between the two is adjusted through a closed-loop regulator.

[0114] Among them, the specific form of the closed-loop regulator is not limited in this embodiment, and a proportional-integral (PI) regulator, a proportional-integral-derivative (PID) regulator or other types of regulators can be used for implementation.

[0115] In addition, the single control loop provided above is only a most basic energy storage device output control scheme for realizing low-frequency oscillation suppression. On this basis, other links can be added to the above single control loop according to different needs in actual applications. For example Figure 3 As shown, in order to protect the subsequent load, a limiter module can be selected to be added at the output end of the closed-loop regulator to limit the dynamic range of the signal amplitude, avoid large-range fluctuations of the signal amplitude, and thus protect the subsequent equipment from high voltage or current impact and prevent hardware burnout caused by transient overload.

[0116] Furthermore, as can be seen from the above embodiments, for the low-frequency oscillation suppression scheme corresponding to step S13, its principle is that the energy storage device shares a part of the load power originally borne by the power grid. That is to say, the load power expected to be shared by the energy storage device in this scheme corresponds to the given value in the above single control loop (if the output of the energy storage device is power, it can be directly used as the given value, otherwise it needs to be converted into the corresponding output as the given value).

[0117] Therefore, regarding how to determine the above output target value as the given value, this embodiment provides a corresponding implementation scheme:

[0118] Obtain the average value of the total load power of the train; determine the target output power of the energy storage device according to the product of the average value of the total load power and a preset suppression coefficient; determine the output target value of the energy storage device according to the target output power value. Among them, the suppression coefficient is any positive number less than or equal to 1.

[0119] In this embodiment, the suppression coefficient is directly used as the standard to measure how much load power the energy storage device shares for the power grid. The output target value determined thereby can adapt to different load power magnitudes, and can ensure the suppression effect of the low-frequency oscillation suppression scheme corresponding to step S13. There is no need to set a suitable output target value specifically each time, further simplifying the control logic and improving the efficiency and timeliness of control response.

[0120] On the other hand, considering that the low-frequency oscillation suppression achieved by either step S12 or step S13 above is based on the discharge of the energy storage device. However, the electric energy that can be stored in the energy storage device is limited after all, and it cannot ensure continuous discharge throughout the entire operation period of the train to suppress low-frequency oscillation. And based on the above principle explanation of the inducement of low-frequency oscillation, under light load conditions, there need to be enough trains in the same power supply section for the harmonic coupling between multiple trains to cause low-frequency oscillation in the power grid. Under non-light load conditions, it is when the capacity of the power supply section does not match the power demand of the load that severe power disturbances will occur in the power supply section, and then low-frequency oscillation of the power grid voltage will be caused. That is to say, low-frequency oscillation does not occur all the time during the operation of the train.

[0121] Therefore, for the above scheme of suppressing low-frequency oscillation by discharging the energy storage device in steps S12 and S13, this embodiment further provides an implementation scheme. Before discharging the energy storage device, it further includes:

[0122] S14: Determine whether low-frequency oscillation exists; if it exists, go to the corresponding step to control the DC inverter to discharge the energy storage device; if it does not exist, stop the operation of the DC inverter.

[0123] That is, before controlling the energy storage device to output electric energy in the manner of steps S12 and S13 in this embodiment, it is first determined whether there is low-frequency oscillation in the current train. If it exists, the low-frequency oscillation is suppressed by the manner of step S12 or S13. Otherwise, the energy storage device is not made to output electric energy to reduce the energy consumption of the energy storage device and prepare for possible suppression of low-frequency oscillation during the subsequent operation of the train.

[0124] Based on this, in a preferred embodiment, the energy storage device can be charged when it is not required to discharge. In view of this, this embodiment provides a possible implementation solution, and this method further includes:

[0125] S21: If there is still remaining capacity after the output power of the four-quadrant converter undertakes the load of the train, control the four-quadrant converter to output at the rated power, and control the energy storage device to work in the charging mode through the DC converter.

[0126] It should be noted that during the operation of the train, there may be a situation where the load power is low, such as when the train is running at a low speed or in a parked state. At this time, there will still be remaining capacity in the power grid on the premise that it can independently undertake the required load power of the train. For this part of the remaining capacity, this embodiment charges the energy storage device by controlling the DC converter, and the energy consumed by the energy storage device during the suppression of low-frequency oscillation can be supplemented without introducing an external charging power source, ensuring that the suppression of low-frequency oscillation implemented based on this method can cover a longer period during the operation of the train and better ensuring the smooth operation of the train.

[0127] Furthermore, in addition to charging the energy storage device through the remaining capacity of the power grid provided in the above embodiment, this embodiment also provides another possible energy storage device charging solution, and this method further includes:

[0128] S22: If the traction motor in the train works in the braking mode, control the traction inverter to work in the braking state, and control the energy storage device to work in the charging mode through the DC converter.

[0129] It is not difficult to understand that during the actual operation of the train, it may enter a long downhill lane. At this time, the train needs to brake for a long time to ensure the vehicle speed. Moreover, generally, the motors in electric locomotives have two modes: traction and braking. When the motor works in the braking mode, electrical energy can be generated. In view of this, this embodiment utilizes the energy generated by braking. When the train is in the braking state, the train does not require power grid power supply to support the load, and thus the low-frequency oscillation problem caused by the above two incentives will not occur. And at this time, the braking energy can be used to charge the energy storage device to make up for the energy consumed by the energy storage device when suppressing low-frequency oscillations. Similar to the above embodiment, this solution is simple to implement, does not require an external power source to charge the energy storage device, can also improve the utilization rate of the train braking energy, and better meets the actual operation needs of the train.

[0130] It should also be noted that in the above embodiment, whether the energy storage device is charging or discharging, it is necessary to judge in combination with the state of charge of the energy storage device itself. For example, when the remaining power (SOC) of the energy storage device is too low, even if the energy storage device needs to discharge, it cannot be realized. Similarly, when the remaining power of the energy storage device is too high, even if the power grid has remaining capacity or the train is working in the braking mode, the energy storage device cannot be charged.

[0131] On the other hand, as can be seen from the solution provided by the above embodiment, the low-frequency oscillation suppression solutions corresponding to steps S12 and S13 are preferably only carried out when the train has a low-frequency oscillation to reduce the unnecessary energy consumption of the energy storage device. The normal grid voltage is mostly a 50Hz sine wave, and the amplitude of its fundamental wave is relatively stable and there is no oscillation. When a low-frequency oscillation occurs, it is equivalent to superimposing a low-frequency sine wave on the 50Hz sine wave, and the two superimposed present a sine wave with an obvious envelope. Therefore, any existing method that can identify the above characteristics can be used to realize the low-frequency oscillation identification required in the above embodiment, and this embodiment does not limit this.

[0132] To better illustrate this method, this embodiment also gives several possible low-frequency oscillation identification solutions:

[0133] 1. Software method: Extract the fundamental wave of the grid voltage through the fast Fourier transform (FFT), and judge whether the fluctuation degree of the wave peak or wave valley of the fundamental wave exceeds the corresponding threshold within a certain period of time. If so, it means that a low-frequency oscillation has occurred.

[0134] 2. Hardware filtering: Extract the fundamental wave in the grid voltage through various digital filters such as notch filters and band-pass filters and send it to the signal processing system for analysis (which can be the same as in the above software method) to judge whether a low-frequency oscillation occurs.

[0135] 3. Other signal processing methods: Broadly speaking, they can be classified into: signal processing-based methods such as wavelet transform, Hilbert-Huang transform (HHT), etc.; model-based methods such as Prony algorithm, eigenvalue analysis method, transfer function / impedance analysis method, etc.; data-driven methods such as machine learning, etc.

[0136] In the application of this method, the above or other low-frequency oscillation recognition methods can be freely selected based on actual needs to identify whether low-frequency oscillation occurs, so as to determine whether it is necessary to execute the low-frequency oscillation suppression scheme provided by this application.

[0137] Furthermore, different from the low-frequency oscillation suppression scheme under light load conditions corresponding to step S12, the scheme corresponding to step S13 is difficult to completely avoid the generation of low-frequency oscillation, mainly playing a role in alleviating low-frequency oscillation to reduce its impact to a negligible level. And the reason why this scheme can achieve low-frequency oscillation suppression is that the energy storage device shares part of the load power for the power grid, thereby reducing the power exchange intensity between the power grid and the train. Therefore, it is not difficult to deduce that in general, the greater the load power shared by the energy storage device, the higher the effect of suppressing low-frequency oscillation. However, due to the limited capacity of the energy storage device, the load power shared by the energy storage device is not the higher the better, but the lower the better on the premise of ensuring the low-frequency oscillation suppression effect.

[0138] In addition, in a further embodiment, the above-mentioned desired load power shared by the energy storage device corresponds to the output target value of the energy storage device in step S131, that is, the given value in the single control loop of the energy storage device. Therefore, regarding how to adjust the output target value of the above-mentioned energy storage device, this embodiment provides a possible implementation scheme. After the above step S131, this method further includes:

[0139] S132: Judge whether the low-frequency oscillation of the train still exists; if so, increase the suppression coefficient to re-determine the output target value of the energy storage device, and return to step S131.

[0140] It can be seen that based on the scheme provided by this embodiment, the control process of suppressing low-frequency oscillation by the energy storage device sharing load power in step S13 can be realized by repeatedly adjusting the output target value (i.e., the shared load power) of the energy storage device multiple times. By setting the initial value and the step size of each adjustment, the output target value can be quickly approximated to the theoretically minimum value (i.e., the lowest output target value required to meet the low-frequency oscillation suppression needs).

[0141] And in a further embodiment described above, the output target value is determined based on the average total load power and the suppression coefficient. Therefore, in this embodiment, when increasing the output target value, it is also achieved by increasing the suppression coefficient. However, the value of the suppression coefficient has an upper limit (i.e., 1), which indicates that the energy storage device cannot output more power than required by the train load, avoiding unnecessary energy consumption and preventing reverse current flowing into the power grid, which may cause other safety hazards. Additionally, it should be noted that the upper limit of "1" is only the theoretical upper limit of the suppression coefficient value. Due to the limited output power of the energy storage device, and the load conditions targeted by step S13 include heavy load conditions, at this time, the energy storage device may not be able to independently bear the load power, that is, even if the suppression coefficient is set to 1, the energy storage device cannot reach the corresponding power output. However, regardless of whether the energy storage device can independently bear the load power, the maximum value of its suppression coefficient can only be taken as 1. And when there is still low-frequency oscillation when the suppression coefficient reaches 1, it cannot be solved by increasing the output target value.

[0142] For this special case, this embodiment also provides a possible solution. This method further includes:

[0143] S133: If there is still low-frequency oscillation in the train when the suppression coefficient increases to 1, gradually reduce the traction power of the train until the low-frequency oscillation of the train is eliminated.

[0144] It can be easily known from the above that when the suppression coefficient increases to 1, the energy storage device reaches the maximum power output theoretically. At this time, if there is still low-frequency oscillation, it indicates that the reason for the low-frequency oscillation is not only insufficient power supply, but the mismatch between the power supply and the load caused by the excessive train load. At this time, this embodiment restricts the power of the train traction load to alleviate the problem of power supply and load mismatch and achieve the suppression of low-frequency oscillation.

[0145] It should be noted that if only starting from the principle of restricting the load to suppress low-frequency oscillation as described above, the type of load restricted does not necessarily have to be the traction load in essence. But as Figure 1 shown, the train load generally includes two types: traction load and auxiliary load. The auxiliary load in the train includes auxiliary systems such as lighting and air conditioning ventilation. These auxiliary systems are crucial for the safety and riding experience of passengers in the train. Therefore, this embodiment alleviates low-frequency oscillation by restricting the traction load in the train load.

[0146] Furthermore, by integrating the above several embodiments for step S13, the low-frequency oscillation suppression process as Figure 4 shown can be obtained. That is, first identify the train load conditions and determine whether there is low-frequency oscillation (there is no restriction on the sequence relationship between the load condition identification and the low-frequency oscillation identification), Figure 4(which is only an optional solution). If there is no low-frequency oscillation, the train still operates according to its original conventional electric traction working mode. If there is low-frequency oscillation, the energy storage device is put into operation to undertake the load power to suppress the low-frequency oscillation. Specifically, when the train is in a light-load condition, the low-frequency oscillation is suppressed by the solution in step S12 above. When the train is in a non-light-load condition, the low-frequency oscillation is suppressed by the solution in step S121 above. Then, it is judged whether the low-frequency oscillation still exists; if it exists, the suppression coefficient is increased, and it is re-judged whether there is low-frequency oscillation; if not, the suppression coefficient for controlling the energy storage device is directly obtained. After that, it is judged whether the suppression coefficient is increased to 1. If the low-frequency oscillation still exists after the suppression coefficient is increased to 1, the traction load is restricted, and it is re-returned to the judgment of whether there is still low-frequency oscillation, and the traction load is further restricted. If the low-frequency oscillation disappears due to the power input of the energy storage device, the final control output signal of the energy storage device is obtained to control the output of the energy storage device and realize the suppression of the low-frequency oscillation.

[0147] On the other hand, in addition to suppressing low-frequency oscillation, the on-vehicle energy storage system provided by the present application can also achieve additional functions or effects due to the addition of the energy storage device. For example, this embodiment provides an additional function realized by the on-vehicle energy storage system. The above method further includes:

[0148] S31: Obtain the instantaneous value of the DC voltage, and extract the instantaneous value of the secondary ripple from the instantaneous value of the DC voltage.

[0149] S32: Determine the secondary ripple amplitude and the secondary ripple inverse proportion coefficient according to the instantaneous value of the secondary ripple; wherein, the secondary ripple inverse proportion coefficient is negatively correlated with the secondary ripple amplitude.

[0150] S33: Control the output of the energy storage device through the secondary ripple suppression strategy.

[0151] S34: The secondary ripple suppression strategy is a double closed-loop control strategy.

[0152] Among them, the outer loop of the secondary ripple suppression strategy is a negative feedback closed-loop control structure with the secondary ripple target given value as the outer loop given quantity and the secondary ripple amplitude as the feedback quantity; the inner loop of the secondary ripple suppression strategy is a negative feedback closed-loop control structure with the product of the output of the outer loop and the secondary ripple inverse proportion coefficient D1 as the inner loop given quantity and the actual output value of the energy storage device as the inner loop feedback quantity.

[0153] In the traditional electric traction mode, since both the AC power grid and the train's AC input current are single-phase, a large secondary pulsation is inevitably generated in the intermediate DC circuit, and the greater the load power, the greater the secondary pulsation. In the scenario where the catenary is de-energized, there is no external energy input to the train, and the DC capacitor voltage in the DC circuit is stable without secondary pulsation. Therefore, the need to suppress secondary pulsation exists in high-power traction scenarios.

[0154] Currently, common secondary pulsation suppression schemes, as Figure 1 shown, can be achieved by adding an inductor-capacitor (LC) resonance circuit in the DC circuit. However, there may be some trains that adopt a circuit topology without an LC resonance circuit, or the LC resonance circuit alone is not sufficient to meet the need for suppressing secondary pulsation. At this time, the scheme provided in the above embodiment can be used to suppress secondary pulsation.

[0155] Specifically, the control scheme implemented by the above steps in this embodiment is as Figure 5 shown:

[0156] The control scheme provided in this embodiment is a double closed-loop control strategy. Among them, the outer loop is the secondary pulsation amplitude control loop, and its input (the given value of the outer loop) is the target given value of the secondary ripple, which can be set to 0 or a very small positive number, that is, it means that based on this control strategy, the secondary ripple is reduced to 0 or close to 0. Then, by sending the instantaneous value of the DC voltage into the secondary ripple extraction module, the instantaneous value S1 of the secondary ripple can be obtained; then, by sending the instantaneous value S1 of the secondary ripple into the secondary ripple amplitude extraction module, the secondary ripple amplitude S2 can be obtained; the difference between the target given value of the secondary ripple and S2 is sent to the pre-stage regulator to obtain the output of the outer loop. Additionally, it should be noted that, similar to the above embodiment and the Figure 3 control scheme shown, other links can also be added to the control process based on actual needs. As Figure 5 shown, a limiting module (i.e., Figure 5 limiting 1) can be added to the output end of the pre-stage regulator to play a protective role.

[0157] The key to pulsation suppression is to adjust the output of the outer loop through the ripple inverse coefficient link to obtain the inner loop given value finally used to control the output of the energy storage device. Since the ripple inverse coefficient is negatively correlated with the instantaneous value of the secondary ripple, the greater the instantaneous value of the secondary ripple, the smaller the ripple inverse coefficient. As the inner loop of the energy storage device output control loop, after obtaining the inner loop given value, it can control the output of the energy storage device to reduce the secondary ripple.

[0158] It should be noted that the secondary ripple suppression scheme provided in this embodiment can replace the original LC resonance circuit to achieve secondary ripple suppression in the DC circuit. Or in another possible implementation, the secondary ripple suppression scheme provided in this embodiment can be implemented together with the original LC resonance circuit to compensate for the secondary ripple in the DC circuit, so that the traction system has a more stable performance. In addition, although this method also controls the energy storage device, this scheme does not conflict with the low-frequency oscillation suppression scheme in the above embodiment, and can be used as an optional function after the in-vehicle energy storage system is deployed to compensate for the secondary ripple in the DC circuit when needed, so that the traction system has a more stable performance.

[0159] Furthermore, regarding how to specifically determine the secondary ripple inverse proportion coefficient in the above embodiment, this embodiment also provides a possible implementation:

[0160] S321: Obtain the historical fluctuation range of the secondary ripple.

[0161] S322: Determine the position of the first quantile of the instantaneous value of the secondary ripple in the historical fluctuation range of the secondary ripple.

[0162] S323: Determine the position of the second quantile according to the complementary mapping of the position of the first quantile.

[0163] S324: Based on the position of the second quantile, determine the corresponding value from the preset inverse proportion coefficient value range as the secondary ripple inverse proportion coefficient.

[0164] Among them, the median of the inverse proportion coefficient value range is 1. Although this embodiment does not limit the upper and lower limits of the inverse proportion coefficient value range, it is not difficult to know that the inverse proportion coefficient cannot take negative values. In a possible embodiment, the inverse proportion coefficient value range can be 0.8 to 1.2.

[0165] Taking the inverse proportion coefficient value range of 0.8 to 1.2 as an example, the process of determining the inverse proportion coefficient in this embodiment is further described:

[0166] The quantile position is a method for characterizing the position of a specific value in a numerical range. Assuming the value is x and the range is [a, b], then the quantile position of x in the range [a, b] is (x - a) / (b - a). Based on this, assuming that the position of the first quantile of the instantaneous value of the secondary ripple in the historical fluctuation range of the secondary ripple is 25%, then the complementary mapping second quantile position of 25% = 1 - 25% = 75%. At this time, the formula for determining the quantile position can be used reversely to obtain the secondary ripple inverse proportion coefficient of 1.1.

[0167] It can be seen that the secondary ripple inverse proportion coefficient determination scheme provided by this embodiment can conveniently and quickly determine the secondary ripple inverse proportion coefficient. Moreover, the determined secondary ripple inverse proportion coefficient D1 can meet the above requirements and has a negative correlation with the fluctuation of the instantaneous value S1 of the secondary ripple. More specifically, there is the following principle for determining the secondary ripple inverse proportion coefficient D1: when S1 is the largest, D1 is the smallest; when S1 is the smallest, D1 is the largest; the value range of D1 fluctuates around 1, such as between 0.8 and 1.2, and the fluctuation direction of D1 is opposite to that of S1, showing a negative correlation.

[0168] On the other hand, in addition to the above secondary pulsation suppression scheme, other functions can also be realized based on the setting of the on-vehicle energy storage system. This embodiment provides a possible implementation scheme, and the above method further includes:

[0169] S41: Control the train to stop traction work and enter the static pantograph-raising state.

[0170] S42: Control the output of the energy storage device through the DC converter to establish the DC bus voltage, and control the four-quadrant converter to work in the inverter mode to deliver capacitive reactive power to the power grid.

[0171] In the actual application scenario of the train, when a heavy-haul train is running in some difficult sections, due to the long power supply arm, the terminal voltage is low, and it is difficult for the train to pass at this time. However, through the terminal voltage boosting scheme provided by this embodiment, the train in some sections can be controlled to stop traction work and be in the static pantograph-raising state; then, the DC voltage is established through the energy storage device and its DC converter; then, the four-quadrant converter works in the inverter mode and delivers capacitive reactive power to the power grid to compensate for the inductive reactive power in the line, achieving the effect of boosting the terminal voltage, thereby helping other trains to pass normally.

[0172] It can be seen that this embodiment based on the on-vehicle energy storage system deployed in the train can also be used to boost the terminal voltage of the power grid. For example, when the train is at the end of the power supply arm, etc., the low network voltage will affect the train operation. At this time, some trains adopting this scheme can be made to stop traction work through this embodiment, and the controller makes the pantograph raise statically; make its working mode change to be equivalent to a capacitive reactive power generator and deliver capacitive reactive power to the power grid; thus achieving the purpose of boosting the terminal voltage and supporting the smooth passage of the remaining trains.

[0173] On the other hand, in addition to the above secondary pulsation suppression and terminal voltage boosting schemes, other functions can also be realized based on the setting of the on-vehicle energy storage system. This embodiment provides a possible implementation scheme, and the above method further includes:

[0174] S51: Control the train to stop traction work and enter the static pantograph-raising state.

[0175] S52: Control the output of the energy storage device through a DC converter to establish the DC bus voltage, and control the four-quadrant converter to operate in the inversion mode to transmit capacitive reactive power or inductive reactive power to the power grid.

[0176] In the actual application scenario of the train, when the train enters certain sections in winter, due to the icing of the power grid, the train may be unable to pass. At this time, based on the solution provided in this embodiment, the on-vehicle energy storage system deployed in the train can be used to raise the pantograph when the train is in a stationary condition and inject inductive or capacitive reactive power into the power grid, so that the power grid cables generate heat and melt the ice, and then the train can drive out of the ice-covered section.

[0177] That is to say, in this embodiment, capacitive reactive power or inductive reactive power is transmitted to the power grid through the output of the energy storage device, so that the power grid generates heat and melts the ice, achieving the effect of AC de-icing. When the icing condition of the power grid is improved, the train can smoothly pass through the ice-covered section.

[0178] Furthermore, the AC de-icing solution provided in the above embodiment is not limited to being realized by a single vehicle or multiple vehicles. A single vehicle can be realized by the above steps S51 and S52. For the AC de-icing between multiple vehicles, this embodiment provides a further implementation solution. The above step S52 is specifically:

[0179] Control the first part of the train to transmit capacitive reactive power to the power grid, and control the second part of the train to transmit inductive reactive power to the power grid.

[0180] Wherein, the sum of the capacitive reactive power transmitted to the power grid by the first part of the train is equal to the sum of the inductive reactive power transmitted to the power grid by the second part of the train.

[0181] That is to say, taking two vehicles as an example, if the two vehicles are separated by a certain distance, one train transmits inductive reactive power to the power grid, and the other vehicle transmits capacitive reactive power of equal capacity to the power grid, then a reactive current path will be generated between the two trains. The reactive current does not need to be obtained from the substation, and the special need of short-distance de-icing can be realized. The same is true when the number of trains exceeds two. As long as it is ensured that the total amount of capacitive reactive power injected into the power grid is equal to the inductive reactive power, other influences of injecting inductive reactive power or capacitive reactive power into the power grid can be avoided on the premise of realizing the AC de-icing function.

[0182] On the other hand, in addition to the above secondary pulsation suppression, end voltage boost, and AC de-icing solutions, other functions can also be realized based on the setting of the on-vehicle energy storage system. This embodiment provides a possible implementation solution. The above method further includes:

[0183] S61: When the train passes through the neutral section, control the energy storage device to supply power to the load of the train through a DC converter.

[0184] That is to say, this embodiment provides a non-stop scheme when the train passes through the neutral section. When the train is in the neutral section area, the power grid is in a de-energized state. At this time, the four-quadrant converter stops working. Then, in this embodiment, through the energy storage device and the DC conversion system, the energy storage system DC-converts to stabilize the intermediate DC voltage to supply power to the traction inverter and the auxiliary inverter, realizing non-stop operation of traction and auxiliary. Therefore, based on the non-stop scheme for passing through the neutral section provided by this embodiment, the train will not stop in the de-energized area due to failure to pass through the neutral section, resulting in a rescue accident, nor will it cause the auxiliary systems such as lighting and air-conditioning equipment to stop working, affecting the riding experience, and achieving better performance.

[0185] In addition, this embodiment also provides another function that can be realized based on the on-vehicle energy storage system. The above method further includes:

[0186] S62: When the power grid loses power or the train runs in a non-electrified railway section, control the energy storage device to supply power to the train load through the DC converter.

[0187] That is to say, this embodiment provides an emergency traction function based on the on-vehicle energy storage system. Under the condition of power grid power failure or in a non-electrified railway section, emergency traction can be provided through the on-vehicle energy storage system, thus avoiding the train stopping in the de-energized area and causing a rescue accident, nor will it cause the auxiliary systems such as lighting and air-conditioning equipment to stop working, affecting the riding experience, and meeting special needs.

[0188] In addition, this embodiment also provides another function that can be realized based on the on-vehicle energy storage system. The above method further includes:

[0189] S63: When the power grid cannot independently bear the train load, control the energy storage device to inject power support into the DC bus through the DC converter, and jointly supply power to the train load with the power grid.

[0190] That is to say, this embodiment provides a hybrid traction function based on the on-vehicle energy storage system. Under extreme line conditions such as heavy-load and large-gradient traction, a hybrid traction mode of the power grid - on-vehicle energy storage system can be adopted, thereby improving the overall traction power of the train and meeting the traction requirements under extreme heavy-load conditions.

[0191] The above has introduced in detail a vehicle-mounted energy storage system and a control method based on the vehicle-mounted energy storage system provided in this application. The various embodiments in the specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the various embodiments, reference can be made to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple. For the relevant parts, reference can be made to the description in the method section. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of this application, several improvements and modifications can still be made to this application, and these improvements and modifications also fall within the protection scope of this application.

[0192] It should also be noted that in this specification, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without more limitations, the element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, article or device including the said element.

Claims

1. A vehicle-mounted energy storage system, characterized in that, Comprising: An energy storage device, a DC converter, and a control device; Wherein, the energy storage device is connected to the DC bus in the train traction system through the DC converter; The DC converter is used to control the energy exchange between the energy storage device and the DC bus; The control device is connected to the DC converter and is used for: if the train is in a light load condition, controlling the energy storage device to independently supply power to the load of the train; if the train is in a non-light load condition, when the train has a low-frequency oscillation, controlling the energy storage device to inject power support into the DC bus.

2. A control method based on an in-vehicle energy storage system, characterized in that, Applied to the on-vehicle energy storage system as described in claim 1, the method includes: Obtaining the current load condition of the train; wherein, the load condition includes: light load condition and non-light load condition; If the load condition is a light load condition, then controlling the four-quadrant converter in the train traction system to stop working, and controlling the DC converter to make the energy storage device independently supply power to the load of the train; If the load condition is a non-light load condition, then when the train has a low-frequency oscillation, controlling the DC converter to make the energy storage device inject power support into the DC bus and jointly supply power to the load of the train with the power grid.

3. The control method based on the in-vehicle energy storage system according to claim 2, wherein The controlling the DC converter to make the energy storage device inject power support into the DC bus and jointly supply power to the load of the train with the power grid includes: Taking the output target value of the energy storage device as the given quantity and the actual output value of the energy storage device as the feedback quantity, and the DC converter performs output control on the energy storage device through a closed-loop regulator; Wherein, the output target value of the energy storage device is determined according to the total load power of the train.

4. The control method based on the vehicle-mounted energy storage system according to claim 3, wherein The method for determining the output target value of the energy storage device includes: Obtaining the average value of the total load power of the train; Determining the output power target value of the energy storage device according to the product of the average value of the total load power and a preset suppression coefficient; wherein, the suppression coefficient is any positive number less than or equal to 1; Determining the output target value of the energy storage device according to the output power target value.

5. The control method based on an in-vehicle energy storage system according to claim 4, wherein After the DC converter performs output control on the energy storage device by taking the output target value of the energy storage device as the given quantity and the actual output value of the energy storage device as the feedback quantity through a closed-loop regulator, it further includes: Judging whether the low-frequency oscillation of the train still exists; If so, increasing the suppression coefficient to re-determine the output target value of the energy storage device, and returning to the step of the DC converter performing output control on the energy storage device by taking the output target value of the energy storage device as the given quantity and the actual output value of the energy storage device as the feedback quantity through a closed-loop regulator.

6. The control method based on the vehicle-mounted energy storage system according to claim 5, wherein It further includes: If the train still has a low-frequency oscillation when the suppression coefficient increases to 1, gradually reducing the traction power of the train until the low-frequency oscillation of the train is eliminated.

7. The control method based on the vehicle-mounted energy storage system according to any one of claims 2 to 6, characterized in that, It further includes: Obtaining the instantaneous DC voltage value, and extracting the instantaneous value of the second harmonic ripple from the instantaneous DC voltage value; According to the instantaneous value of the second harmonic ripple, determining the amplitude of the second harmonic ripple and the inverse proportional coefficient of the second harmonic ripple; wherein, the inverse proportional coefficient of the second harmonic ripple is negatively correlated with the amplitude of the second harmonic ripple. Control the output of the energy storage device through a secondary pulsation suppression strategy; The secondary pulsation suppression strategy is a double closed-loop control strategy; among them, the outer loop of the secondary pulsation suppression strategy is a negative feedback closed-loop control structure with the secondary ripple target given value as the outer loop given quantity and the secondary ripple amplitude as the feedback quantity; the inner loop of the secondary pulsation suppression strategy is a negative feedback closed-loop control structure with the product of the output of the outer loop and the secondary ripple inverse coefficient as the inner loop given quantity and the actual output value of the energy storage device as the inner loop feedback quantity.

8. The control method based on the vehicle-mounted energy storage system according to claim 7, characterized in that, Determining the secondary ripple inverse coefficient according to the instantaneous value of the secondary ripple includes: Obtain the historical fluctuation range of the secondary ripple; Determine the first quantile position of the instantaneous value of the secondary ripple in the historical fluctuation range of the secondary ripple; Determine the second quantile position according to the complementary mapping of the first quantile position; Based on the second quantile position, determine the corresponding value from the preset inverse coefficient value range as the secondary ripple inverse coefficient; Among them, the median of the inverse coefficient value range is 1.

9. The control method based on the in-vehicle energy storage system according to any one of claims 2 to 6, characterized in that It also includes: Control the train to stop traction operation and enter the static pantograph-raising state; Control the output of the energy storage device through the DC converter to establish the DC bus voltage, and control the four-quadrant converter to operate in the inverter mode to deliver capacitive reactive power to the power grid.

10. The control method based on the vehicle-mounted energy storage system according to any one of claims 2 to 6, characterized in that, It also includes: Control the train to stop traction operation and enter the static pantograph-raising state; Control the output of the energy storage device through the DC converter to establish the DC bus voltage, and control the four-quadrant converter to operate in the inverter mode to deliver capacitive or inductive reactive power to the power grid.

11. The control method based on an in-vehicle energy storage system according to claim 10, characterized in that, The train is multiple; Then the control of the four-quadrant converter to operate in the inverter mode to deliver capacitive or inductive reactive power to the power grid includes: Control the first part of the train to deliver capacitive reactive power to the power grid and control the second part of the train to deliver inductive reactive power to the power grid; Among them, the sum of the capacitive reactive power delivered to the power grid by the first part of the train is equal to the sum of the inductive reactive power delivered to the power grid by the second part of the train.

12. The control method based on the vehicle-mounted energy storage system according to any one of claims 2 to 6, characterized in that, It also includes: If the output power of the four-quadrant converter still has remaining capacity after bearing the load of the train, control the four-quadrant converter to output at the rated power and control the energy storage device to operate in the charging mode through the DC converter.

13. The control method based on the vehicle-mounted energy storage system according to any one of claims 2 to 6, characterized in that, It also includes: If the traction motor in the train operates in the braking mode, control the traction inverter to operate in the braking state and control the energy storage device to operate in the charging mode through the DC converter.

14. The control method based on the vehicle-mounted energy storage system according to any one of claims 2 to 6, characterized in that, It also includes: When the train passes through the neutral section, control the energy storage device to supply power to the load of the train through the DC converter.

15. The control method based on an in-vehicle energy storage system according to any one of claims 2 to 6, characterized in that It also includes: When the power grid loses power or the train runs in a non-electrified railway section, control the energy storage device to supply power to the load of the train through the DC converter.

16. The control method based on the vehicle-mounted energy storage system according to any one of claims 2 to 6, characterized in that It also includes: When the power grid cannot independently bear the load of the train, control the energy storage device to inject power support into the DC bus through the DC converter and jointly supply power to the load of the train with the power grid.

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