A vehicle-mounted energy storage system and a control method based on the vehicle-mounted energy storage system

Abstract

The present application discloses an on-board energy storage system and a control method based on the on-board energy storage system, which relate to the field of rail transit AC transmission control. In view of the fact that traditional low-frequency oscillation suppression schemes mostly focus on the improvement of power supply regulation or grid-side control, an on-board energy storage system is provided, which can use energy sources outside the power grid to replace or share the load power borne by the power grid. Under light-load conditions, the on-board energy storage system completely replaces the power grid to bear the train load power. At this time, the train does not need power supply from the power grid, and there is no harmonic coupling with other trains, which fundamentally solves the cause of low-frequency oscillation. Under heavy-load conditions, the energy storage device can also share part of the train load power, 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 supply from the power grid and the load.

Description

Technical Field

[0001] The present application relates to the field of rail transit AC transmission control, and in particular to an on-board energy storage system and a control method based on the on-board energy storage system. Background Art

[0002] Low-frequency oscillations are a key technical issue in the actual operation of heavy-load or high-speed trains. Due to their complex causes and the interdisciplinary nature of these issues, the technical complexity lies at multiple levels, including power electronics, control theory, electromechanical coupling, and system stability. Furthermore, once low-frequency oscillations occur during train operation, they inevitably have a serious impact on railway safety and operational order. Therefore, suppressing low-frequency oscillations during train operation has always been a key concern and a challenge for those skilled in the art.

[0003] Currently, research on suppressing low-frequency oscillations focuses on improving power supply conditions or improving performance through grid-side control. While application scenarios are limited, the effectiveness of suppressing low-frequency oscillations is also restricted by the grid.

[0004] Therefore, technicians in this field are in urgent need of an on-vehicle energy storage system to provide a new idea and solution to solve the problem of suppressing low-frequency oscillations. Summary of the Invention

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

[0006] To solve the above technical problems, the present application provides a vehicle-mounted energy storage system, comprising: 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 to: if the train is in a light-load condition, control 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, control the energy storage device to input power support into the DC bus.

[0010] To solve the above technical problems, the present application further provides a control method based on a vehicle-mounted energy storage system, which is applied to the above-mentioned vehicle-mounted energy storage system, and the method includes:

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

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

[0013] If the load condition is a non-light load condition, when low-frequency oscillation occurs in the train, the DC converter is controlled to enable the energy storage device to input 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, controlling the DC converter to enable the energy storage device to input power support into the DC bus to jointly supply power to the load of the train with the power grid includes:

[0015] The output target value of the energy storage device is used as a given value, and the actual output value of the energy storage device is used as a feedback value, and the DC converter controls the output of the energy storage device through a closed-loop regulator;

[0016] 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, a method for determining an output target value of the energy storage device includes:

[0018] Obtaining an average total load power of the train;

[0019] 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;

[0020] An output target value of the energy storage device is determined according to the output power target value.

[0021] In a possible embodiment, after the DC converter controls the output of the energy storage device through a closed-loop regulator using the output target value of the energy storage device as a given value and the actual output value of the energy storage device as a feedback value, the method further includes:

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

[0023] If so, increase the suppression coefficient to redetermine the output target value of the energy storage device, and return to the step of 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, and the DC converter controls the output of the energy storage device through a closed-loop regulator.

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

[0025] If the train still has low-frequency oscillations when the suppression coefficient is increased to 1, the traction power of the train is gradually reduced until the low-frequency oscillations of the train are eliminated.

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

[0027] Acquiring an instantaneous value of a DC voltage, and extracting an instantaneous value of a secondary ripple from the instantaneous value of the DC voltage;

[0028] Determining a secondary ripple amplitude and a secondary ripple inverse proportionality coefficient according to the secondary ripple instantaneous value; wherein the secondary ripple inverse proportionality coefficient is negatively correlated with the secondary ripple amplitude;

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

[0030] The secondary pulsation suppression strategy is a dual 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 set value as the outer loop set 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 outer loop output and the secondary ripple inverse proportional coefficient as the inner loop set 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 secondary ripple instantaneous value includes:

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

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

[0034] determining a second quantile position based on a complementary mapping of the first quantile position;

[0035] Based on the second quantile position, determining a corresponding value from a preset inverse proportional coefficient value interval as the secondary ripple inverse proportional coefficient;

[0036] The median value of the inverse proportional coefficient value interval is 1.

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

[0038] Controlling the train to stop traction and enter a stationary pantograph raising state;

[0039] The output of the energy storage device is controlled by the DC converter to establish a DC bus voltage, and the four-quadrant converter is controlled to operate in an inverter mode to deliver capacitive reactive power to the power grid.

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

[0041] Controlling the train to stop traction and enter a stationary pantograph raising state;

[0042] The output of the energy storage device is controlled by the DC converter to establish a DC bus voltage, and the four-quadrant converter is controlled to operate in an inverter mode to deliver capacitive reactive power or inductive reactive power to the power grid.

[0043] In a possible embodiment, the train consists of multiple vehicles;

[0044] Then, controlling the four-quadrant converter to operate in an inverter mode to transmit capacitive reactive power or inductive reactive power to the power grid includes:

[0045] Controlling the train in the first part to deliver capacitive reactive power to the power grid, and controlling the train in the second part to deliver inductive reactive power to the power grid;

[0046] The sum of the capacitive reactive power delivered to the power grid by the trains in the first part is equal to the sum of the inductive reactive power delivered to the power grid by the trains in the second part.

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

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

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

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

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

[0052] When the train is over-phased, the energy storage device is controlled by the DC converter to supply power to the load of the train.

[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, the energy storage device is controlled by the DC converter to supply power to the load of the train.

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

[0056] When the power grid cannot independently bear the load of the train, the DC converter controls the energy storage device to input power support into the DC bus, and the energy storage device and the power grid jointly supply power to the load of the train.

[0057] The on-board energy storage system provided by the present application adds an energy storage device and a DC converter that controls its input / output to the train, so that when the train has low-frequency oscillations or is in a working condition that is extremely prone to low-frequency oscillations, power is supplied to the train DC bus through the energy storage device. Among them, if the energy storage device can independently bear the power supply needs 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 realize the power supply of the train load. At this time, since the train does not need to be powered by the power grid, the train does not need to be connected to the Internet, and there will be no coupling with other trains on the power grid, which can avoid the generation of low-frequency oscillations. When the energy storage device cannot independently bear the power supply needs of the train load, the energy storage device can jointly power the train load with the power grid. 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, which also reduces the power exchange intensity between the train and the power supply system, and the low-frequency oscillation 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 that is distinct from improving power supply conditions or grid-side control performance, offering a new solution and approach to preventing low-frequency oscillations that may occur during train operation. Furthermore, the low-frequency oscillation suppression implemented in this application can be adapted to various train load conditions, achieving good suppression results.

[0059] The control method based on the vehicle-mounted energy storage system provided in this application corresponds to the above-mentioned vehicle-mounted energy storage system and has the same effect as above. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0061] Figure 1 A structural diagram of a vehicle-mounted energy storage system provided by the present invention;

[0062] Figure 2 A flow chart of a control method based on a vehicle-mounted energy storage system provided by the present invention;

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

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

[0065] Figure 5 This is a control block diagram of a secondary pulsation suppression solution provided by the present invention. DETAILED DESCRIPTION

[0066] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0067] The core of this 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 present application, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0069] During the actual operation of AC transmission electric locomotives, various serious faults often occur due to vehicle-grid coupling, among which the more typical ones are:

[0070] On some older lines, certain power supply sections often have insufficient capacity, yet multiple trains may be heavily loaded in these sections due to scheduling issues. This mismatch between power supply and load can lead to severe power disturbances in these sections. This can cause low-frequency oscillations in the grid voltage, triggering overcurrent and overvoltage failures in substations or trains, and severely disrupting normal railway operations.

[0071] 2. In railway stations, many locomotives or EMUs are often parked in the same power supply section. Even though the trains are lightly loaded, harmonic coupling between the trains can still cause low-frequency oscillations in the power grid, leading to widespread train failures within the station, serious accidents, and significant disruptions to railway transportation.

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

[0073] To solve the above problems, the present application provides a vehicle-mounted energy storage system, such as Figure 1 As shown, it includes: 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 to: if the train is in a light-load condition, control the energy storage device to independently supply power to the train's load; if the train is in a non-light-load condition, when low-frequency oscillation occurs in the train, control the energy storage device to input power support into the DC bus.

[0075] In the above-mentioned onboard energy storage system, the energy storage device can be a large-capacity power storage device such as a power battery. Its specifications and parameters should be determined by the actual train traction power supply requirements, and this embodiment does not impose any restrictions on 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. Its specific model and specifications should be determined according to the control requirements of the energy storage device.

[0076] It should be noted that the above-mentioned control device can be an additional digital signal processor (DSP), microcontroller unit (MCU) and other control devices, which are used to specifically control the input or output of the energy storage device. In addition, the above-mentioned control device can also reuse the control equipment of the train's original electric traction system that controls various devices including the four-quadrant converter, so as to integrate the input and output control of the newly added energy storage device into the train traction control, which reduces the additional hardware cost while also helping to ensure that the energy storage device does not have an adverse effect 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 a communication connection with devices such as the four-quadrant converter, traction inverter, and auxiliary inverter. Based on the uncertainty of the connection relationship of the control device in different implementation plans, Figure 1 The control devices and their connections are not shown, but this does not mean that Figure 1 The on-board energy storage system shown does not have the above-mentioned control device, and the control device may be shared with the original train traction system.

[0077] In addition, it can be seen from the above that the on-board energy storage system provided by this application is connected to the DC bus of 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 normally, the energy storage device can be idle or can be used together with the power grid to supply power to the train load (such as Figure 1 The traction load and auxiliary load in Figure 1 The catenary in the train is another name for the power grid) and when the grid is out of power or the four-quadrant converter stops working, the energy storage device can also replace the grid to supply power to the train load.

[0078] From the cause 2 of low-frequency oscillation summarized in the above description, it can be seen that if the energy storage device can replace the power grid to supply power to the train load, the train will not need to access the grid (grid), and there will be no harmonic coupling between multiple trains, thus fundamentally solving the low-frequency oscillation problem.

[0079] Relatedly, when a train is in a light-load condition such as parking inside a station, the 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 create an intermediate DC voltage through diode rectification.

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

[0083] The drawback of control method 1) is that due to the large number of trains within the station, a large number of unloaded AC trains running in the same power supply area can easily induce low-frequency oscillations due to mutual coupling. Another drawback of control method 1) is that the sudden activation of large loads (such as auxiliary loads) can impact the DC circuit, making the train prone to undervoltage faults. While control method 3) combines the advantages of the previous two methods, its drawback is the complex logic and timing, making its engineering application more cumbersome.

[0084] The low-frequency oscillation suppression achieved by the onboard energy storage system provided by this application under lightly loaded train conditions avoids the problems encountered by the three common control methods in the aforementioned related technologies. It completely avoids the occurrence of low-frequency oscillations caused by resonant coupling between multiple trains; it can also withstand the sudden application of large-capacity auxiliary loads without causing the train to report an undervoltage fault; and, because the motor power is low, low-speed, low-power traction is possible without starting the four-quadrant converter, reducing mutual interference between the numerous AC trains within the station, making it a very safe solution.

[0085] In addition, the energy storage device replaces the power grid to independently supply power to the train load, which 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 energy storage device can be controlled by the DC converter to share part of the load power originally provided by the power grid. That is, the energy storage device is used to supply power to reduce the energy obtained by the train from the power grid, reducing the power exchange intensity between the train and the power supply system. Based on this, it can be deduced from the principle of low-frequency oscillation generated by inducement 2 above that the low-frequency oscillation of the power grid will be alleviated at this time.

[0086] Furthermore, it should be noted that while the above description of this embodiment uses light-load and heavy-load operating conditions to illustrate how to suppress low-frequency oscillations of the train, it does not actually limit the specific criteria for defining light and heavy loads. As can be seen above, under light-load conditions, the energy storage device completely replaces the grid in assuming the train load power. This implicitly implies that the total train load power is less than or equal to the maximum output power (rated power) of the energy storage device. Similarly, under heavy-load conditions, the energy storage device cannot independently assume the total train load power. Therefore, it chooses to share the total train load power with the grid to reduce the power exchange intensity between the train and the grid, thereby alleviating low-frequency oscillations of the grid. In other words, the heavy-load condition implicitly implies that the total train power load exceeds the maximum output power (rated power) of the energy storage device. Therefore, the light and heavy load conditions mentioned above in this embodiment can be defined based on the 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 needs that may arise in actual applications, train load conditions may require differentiation beyond light-load and heavy-load conditions. Regardless of the number of train load conditions, they can be distinguished by whether they are light-load conditions. Conditions where the load power can be independently supported by the energy storage device are considered light-load conditions, while all other conditions are considered non-light-load conditions, and low-frequency oscillations can be suppressed using the corresponding solutions for heavy-load conditions.

[0088] In summary, the present application is based on the setting of the on-board energy storage system, and can use energy sources 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-board energy storage system can completely replace the power grid to bear the train load power. At this time, the train does not need to be connected to the Internet, and there is no harmonic coupling with other trains, which fundamentally solves the inducement of low-frequency oscillations. Under heavy load conditions, even if the energy storage device cannot completely replace the power grid to bear the train load power, it can share 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 supply of the power grid and the load. It can be seen that this system can provide corresponding low-frequency oscillation suppression solutions for two different inducements of low-frequency oscillations generated by the train. It is applicable to light load, heavy load and other working conditions of the train, covering various situations that may occur in the actual operation of the train, and is suitable for the new construction of electric locomotives or the transformation of old electric locomotives, greatly improving the availability of the train and its adaptability to the power grid, and enhancing the reliability of railway transportation.

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

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

[0091] The load conditions include light load conditions and non-light load conditions.

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

[0093] S13: If the load condition is not a light load condition, when low-frequency oscillation occurs in the train, the DC converter is controlled to enable the energy storage device to input power support into the DC bus, and jointly supply power to the train load with the power grid.

[0094] For step S11, it can be seen from the above-mentioned embodiment of the on-board energy storage system that the light-load condition and non-light-load condition distinguished here are only a simple load condition distinction 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 light-load conditions and non-light-load conditions. In addition, the definition of whether the load condition is a light-load condition can be determined based on the maximum output power of the energy storage device. Of course, load conditions can also be distinguished based on other parameters. For example, in one possible implementation scheme, this embodiment also provides another definition standard for light-load conditions: train load power ≤ 10% of the single motor power.

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

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

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

[0098] Furthermore, the medium load condition and the heavy load condition in this embodiment both belong to the above-mentioned non-light load condition, and low-frequency oscillation is suppressed by the control scheme corresponding to step S13.

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

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

[0101] For example, Figure 1 As shown, this step is to obtain the motor power borne by the traction inverter and the auxiliary load power borne by the auxiliary inverter in the train traction system respectively, 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 by means of load power observation.

[0103] This load acquisition method is typically implemented in the controller of a four-quadrant converter. Since the four-quadrant converter (grid) in the original train traction system carries all the train load, the output power of the four-quadrant converter is also the total power required by the train load.

[0104] S11-3: The DC bus voltage value and the DC bus current value are obtained through the voltage sensor and the current sensor installed in the intermediate DC circuit, and the load power is obtained by the product of the DC bus voltage value and the DC bus current value.

[0105] This solution is similar to the above-mentioned solution S11-3. It is also based on the characteristic that the intermediate DC circuit is responsible for powering all loads. By obtaining the voltage and current on the intermediate DC circuit, the power on the intermediate DC circuit is directly calculated based on the power calculation formula, that is, the total power at the load end.

[0106] It should be noted that the several load power acquisition and load condition identification schemes provided in the above embodiment are only one possible implementation plan. In actual applications, load power can also be obtained by other means to determine whether the current train load is in a light load condition or other conditions, so as to select a suitable low-frequency oscillation suppression scheme.

[0107] Subsequently, steps S12 and S13, as described in the embodiment of the on-board energy storage system, are low-frequency oscillation suppression schemes for two different train load conditions. For example, in step S12, when the train is in a light-load condition, the train load is relatively small. At this time, the energy storage device can replace the grid to bear all the power required by the train load. In other words, at this time, the four-quadrant converter can stop operating, the train is disconnected from the grid, and the grid does not need to supply power to the train. Because the train is disconnected from the grid, there is no resonant coupling between the trains, and the resulting low-frequency oscillations will not occur. Similarly, in step S13, when the train is in a non-light-load condition, the energy storage device cannot bear the entire train load power alone, and the low-frequency oscillation suppression scheme of step S12 is no longer applicable. In this case, as in step S13, a method of jointly supplying power to the train load using the grid and the energy storage device can be adopted to provide the necessary power support for the train load. In this case, compared to the original situation where the grid alone bears the entire train load power, the power exchange intensity between the grid and the train can be reduced, thereby alleviating the low-frequency oscillation problem caused by the mismatch between grid power supply and load.

[0108] It can be seen that the control method based on the on-board energy storage system provided by the present application can, through the on-board energy storage system provided by the above embodiment, provide a targeted solution to the cause of the low-frequency oscillation problem when the train is in different load conditions. Thereby achieving the effect of adapting to various working conditions of the train in actual operation and suppressing low-frequency oscillations. Moreover, this method is a low-frequency oscillation suppression solution that is different from improving power supply regulation and improving control performance on the grid side, and provides new ideas and means for solving the low-frequency oscillation problem of trains.

[0109] On the other hand, the low-frequency oscillation suppression scheme corresponding to step S13 above shows that as long as the energy storage device shares a portion of the load power for the power grid, it can achieve a certain low-frequency oscillation suppression effect. The output power of the energy storage device and the specific output control scheme adopted only differ in the effectiveness of the suppression. To this end, this embodiment also provides a further implementation scheme of step S13, which specifically includes:

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

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

[0112] In this embodiment, to ensure that the normal traction load and auxiliary load are not affected, the DC bus voltage is still controlled by the four-quadrant converter. The DC converter adopts a single control loop operating mode to control the output of the energy storage device. 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 rather on the output (output current or output power) of the energy storage device. In closed-loop control, the feedback variable is the actual value (i.e., instantaneous value) of the energy storage device's output. Furthermore, the setpoint for closed-loop control is the target value for the energy storage device's output (e.g., the expected output value of the energy storage device when carrying the planned load power). The difference between the two values ​​is adjusted by a closed-loop regulator.

[0114] The embodiment does not limit the specific form of the closed-loop regulator, and a proportional-integral (PI) regulator, a proportional-integral-derivative (PID) regulator, or other types of regulators may be used for implementation.

[0115] In addition, the single control loop provided above is only a basic solution for output control of energy storage device to achieve low-frequency oscillation suppression. On this basis, other links can be added to the single control loop in combination with different needs in actual applications. For example Figure 3 As shown, in order to protect the downstream load, a limiting module can be added at the output end of the closed-loop regulator to limit the dynamic range of the signal amplitude and avoid large fluctuations in the signal amplitude. This can also protect the downstream equipment from excessive voltage or current shocks and prevent hardware burning due to transient overload.

[0116] Furthermore, as can be seen from the above embodiment, the principle behind the low-frequency oscillation suppression solution corresponding to step S13 is to use the energy storage device to share a portion of the load power originally borne by the power grid. In other words, the load power expected to be shared by the energy storage device in this solution corresponds to the set value in the aforementioned single control loop (if the output of the energy storage device is power, it can be used directly as the set value; otherwise, it must be converted to the corresponding output value to serve as the set value).

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

[0118] Obtaining the average total load power of the train; determining the target output power value of the energy storage device based on the product of the average total load power and a preset suppression coefficient; and determining the target output value of the energy storage device based on the target output power value. The suppression coefficient is any positive number less than or equal to 1.

[0119] In this embodiment, the suppression coefficient is used directly as a measure of the load power shared by the energy storage device on the grid. The output target value thus determined can adapt to different load power levels and can consistently guarantee the suppression effect of the corresponding low-frequency oscillation suppression scheme in step S13. This eliminates the need to specifically set an appropriate output target value each time, further simplifying the control logic and improving efficiency and timeliness of control response.

[0120] On the other hand, considering that the low-frequency oscillation suppression achieved in both step S12 and step S13 is achieved based on the discharge of the energy storage device. However, the electrical energy that can be stored in the energy storage device is limited after all, and it cannot be guaranteed to be continuously discharged during the entire operation period of the train to suppress low-frequency oscillations. In addition, based on the above-mentioned explanation of the principle of inducement for low-frequency oscillations, it can be seen that under light-load conditions, there must be enough trains in the same power supply interval before low-frequency oscillations will occur in the power grid due to harmonic coupling between multiple trains. Under non-light-load conditions, it is when the capacity of the power supply interval does not match the power requirements of the load that severe power disturbances will occur in the power supply interval, which in turn will cause low-frequency oscillations in the grid voltage. In other words, low-frequency oscillations do not occur all the time during the operation of the train.

[0121] Therefore, this embodiment provides a further implementation scheme for suppressing low-frequency oscillation by discharging the energy storage device in steps S12 and S13, which further includes the following steps before discharging the energy storage device:

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

[0123] That is, before controlling the energy storage device to output power through steps S12 and S13, this embodiment first determines whether low-frequency oscillations exist on the current train. If so, the low-frequency oscillations are suppressed through steps S12 or S13. Otherwise, the energy storage device is not enabled to output power, thereby reducing its energy consumption and preparing for the potential need to suppress low-frequency oscillations during subsequent train operation.

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

[0125] S21: If the output power of the four-quadrant converter still has residual capacity after bearing the load of the train, the four-quadrant converter is controlled to output at rated power, and the energy storage device is controlled to operate in charging mode through the DC converter.

[0126] It should be noted that during the operation of the train, there may be situations where the load power is low, such as when the train is running at low speed or is parked. At this time, the power grid will still have surplus capacity under the premise that it can independently bear the load power required by the train. For this part of the surplus capacity, this embodiment controls the DC converter to charge the energy storage device, and can replenish the energy consumed by the energy storage device when suppressing low-frequency oscillations without introducing an external charging source. This ensures that the low-frequency oscillation suppression achieved based on this method can cover a longer period of time during the train operation, better ensuring the smooth operation of the train.

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

[0128] S22: If the traction motor in the train operates in a braking mode, the traction inverter is controlled to operate in a braking state, and the energy storage device is controlled to operate in a charging mode through the DC converter.

[0129] It is not difficult to understand that during the actual operation of the train, the train may enter a long downhill lane. At this time, the train needs to brake for a long time to ensure the speed. In addition, the motors in electric locomotives currently generally have two modes: traction and braking. When the motor works in the braking mode, it can generate electrical energy. In view of this, the present embodiment utilizes this part of the energy generated by braking. When the train is in a braking state, the train does not need power supply from the grid to support the load, and the low-frequency oscillation problem caused by the above two inducements 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, and there is no need to introduce an external power supply to charge the energy storage device. It can also improve the utilization rate of the train's braking energy, better meeting the needs of the actual operation of the train.

[0130] It should also be noted that in the above embodiments, whether charging or discharging the energy storage device, the determination must be made in conjunction with the energy storage device's own state of charge. For example, if the remaining charge (SOC) of the energy storage device is too low, discharging the energy storage device cannot be performed even if required. Similarly, if the remaining charge of the energy storage device is too high, the energy storage device cannot be charged, even if the grid has excess capacity or the train is operating in braking mode.

[0131] On the other hand, it can be seen from the scheme provided by the above embodiment that the low-frequency oscillation suppression scheme corresponding to steps S12 and S13 is preferably performed only when low-frequency oscillation occurs in the train, so as to reduce 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 low-frequency oscillation occurs, it is equivalent to superimposing a low-frequency sine wave on the 50Hz sine wave, and the superposition of the two presents a sine wave with a clear envelope. Therefore, any existing method that can identify the above characteristics can be used to achieve 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 provides several possible low-frequency oscillation identification solutions:

[0133] 1. Software method: Extract the fundamental wave of the grid voltage through Fast Fourier Transform (FFT) and determine whether the fluctuation degree of the fundamental wave's peak or trough exceeds the corresponding threshold over a period of time. If so, it indicates that low-frequency oscillation has occurred.

[0134] 2. Hardware filtering: The fundamental wave in the grid voltage is extracted through various digital filters such as notch filters and bandpass filters, and sent to the signal processing system for analysis (the same as the above software method) to determine whether low-frequency oscillation occurs.

[0135] 3. Other signal processing methods: In a broad sense, 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, transfer function / impedance analysis, etc.; data-driven methods, such as machine learning, etc.

[0136] In the application of this method, based on actual needs, one can freely select the above or other low-frequency oscillation identification methods to identify whether low-frequency oscillation occurs, so as to determine whether the low-frequency oscillation suppression solution provided in this application needs to be executed.

[0137] Furthermore, unlike 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 oscillations, and mainly plays the role of alleviating low-frequency oscillations so that the impact thereof is reduced 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, under normal circumstances, the greater the load power shared by the energy storage device, the higher the effect of suppressing low-frequency oscillations. 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 under the premise of ensuring the low-frequency oscillation suppression effect.

[0138] Furthermore, in a further embodiment, the load power expected to be shared by the energy storage device corresponds to the target output value of the energy storage device in step S131, i.e., the given value in the single control loop of the energy storage device. Therefore, this embodiment provides a possible implementation plan for adjusting the target output value of the energy storage device. After step S131, the method further includes:

[0139] S132: Determine 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] Thus, based on the solution provided by this embodiment, the control process of using the energy storage device to share load power to suppress low-frequency oscillations in step S13 can be achieved by repeatedly adjusting the output target value of the energy storage device (i.e., the shared load power). By setting an initial value and the step size for each adjustment, the output target value can be quickly brought close to the theoretical minimum value (i.e., the lowest output target value required to suppress low-frequency oscillations).

[0141] Furthermore, 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, increasing the output target value is also achieved by increasing the suppression coefficient. However, the suppression coefficient has an upper limit (i.e., 1), which indicates that the energy storage device cannot output power exceeding the power required by the train load, avoiding unnecessary energy consumption and preventing current from flowing back into the power grid and creating other safety hazards. It should also be noted that the upper limit of "1" is only a theoretical upper limit for the suppression coefficient. Because the output power of the energy storage device is limited, and the load conditions addressed in step S13 include heavy load conditions, the energy storage device may not be able to independently bear the load power. In other words, even if the suppression coefficient is set to 1, the energy storage device will not achieve the corresponding power output. However, regardless of whether the energy storage device can independently bear the load power, its maximum suppression coefficient can only be 1. Furthermore, if low-frequency oscillations still exist even when the suppression coefficient reaches 1, it cannot be resolved by increasing the output target value.

[0142] In view of this special situation, this embodiment also provides a possible solution, and the method further includes:

[0143] S133: If the train still has low-frequency oscillations when the suppression coefficient is increased to 1, the traction power of the train is gradually reduced until the low-frequency oscillations of the train are eliminated.

[0144] From the above, it is clear that when the suppression coefficient increases to 1, the energy storage device reaches its theoretical maximum power output. If low-frequency oscillations still exist at this point, it indicates that the cause of the low-frequency oscillations is not simply insufficient power supply, but rather a mismatch between the power supply and the load caused by the excessive train load. In this case, this embodiment mitigates the power mismatch by limiting the power of the train's traction load, thereby suppressing the low-frequency oscillations.

[0145] It should be noted that if we only consider the principle of limiting the load to suppress low-frequency oscillation, the load type to be limited does not necessarily have to be a traction load. Figure 1 As shown, train loads typically include traction loads and auxiliary loads. Auxiliary loads correspond to auxiliary systems in the train, such as lighting, air conditioning, and ventilation. These auxiliary systems are crucial to passenger safety and the riding experience. Therefore, this embodiment mitigates low-frequency oscillations by limiting the traction load within the train load.

[0146] Furthermore, based on the above several embodiments for step S13, we can obtain the following: Figure 4 The low-frequency oscillation suppression process shown in the figure is to first identify the train load condition and determine whether there is low-frequency oscillation (there is no order restriction between load condition identification and low-frequency oscillation identification. Figure 4Only one optional solution). If there is no low-frequency oscillation, the train will continue to operate in accordance with its original conventional electric traction working mode. If there is low-frequency oscillation, the energy storage device will be put into operation to bear 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 of step S12 above; when the train is in a non-light-load condition, the low-frequency oscillation is suppressed by the solution of step S121 above. Afterwards, it is determined whether the low-frequency oscillation still exists; if so, the suppression coefficient is increased, and it is re-determined whether there is low-frequency oscillation; if not, the suppression coefficient for energy storage device control is directly obtained. Afterwards, it is determined 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 limited, and the judgment of whether there is still low-frequency oscillation is returned, and the traction load is further limited. If the low-frequency oscillation disappears based on 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 to achieve the suppression of low-frequency oscillation.

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

[0148] S31: Acquire 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 proportionality coefficient according to the secondary ripple instantaneous value; wherein the secondary ripple inverse proportionality coefficient is negatively correlated with the secondary ripple amplitude.

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

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

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

[0153] In traditional electric traction, since both the AC grid and the train's AC input current are single-phase, significant secondary pulsation inevitably occurs in the intermediate DC circuit. This pulsation increases with load power. However, in scenarios where the overlying grid is depleted, the train receives no external energy input, and the DC capacitor voltage in the DC circuit remains stable, eliminating secondary pulsation. Therefore, secondary pulsation suppression is essential in high-power traction scenarios.

[0154] At present, common secondary pulsation suppression solutions are as follows: Figure 1 As shown, this can be achieved by adding an inductor-capacitor (LC) resonant circuit to the DC link. However, some trains may use a circuit topology without an LC resonant circuit, or the LC resonant circuit alone may not be sufficient to suppress secondary pulsation. In such cases, the solution provided above in this embodiment can suppress secondary pulsation.

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

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

[0157] The key to pulsation suppression lies in adjusting the outer loop output through the ripple inverse proportionality factor to obtain the inner loop setpoint used to control the energy storage device output. Because the ripple inverse proportionality factor is negatively correlated with the instantaneous value of the secondary ripple, the larger the instantaneous value of the secondary ripple, the smaller the ripple inverse proportionality factor. Once the inner loop, which controls the energy storage device output, obtains the inner loop setpoint, it can control the energy storage device output to reduce the secondary ripple.

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

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

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

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

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

[0163] S324: Based on the second quantile position, determine a corresponding value from a preset inverse proportional coefficient value interval as the secondary ripple inverse proportional coefficient.

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

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

[0166] The quantile position is a method used to characterize the position of a specific value within a numerical range. For example, if the value is x and the interval is [a, b], then the quantile position of x within the interval [a, b] is (xa) / (ba). Based on this, assuming the first quantile position of the instantaneous value of the secondary ripple within the historical fluctuation range of the secondary ripple is 25%, then the second quantile position of the complementary mapping of 25% = 1-25% = 75%. At this point, the above quantile position determination formula can be reversed to obtain the inverse proportionality coefficient of the secondary ripple as 1.1.

[0167] Thus, the secondary ripple inverse proportionality coefficient determination scheme provided in this embodiment can quickly and easily determine the secondary ripple inverse proportionality coefficient. Furthermore, the determined secondary ripple inverse proportionality coefficient D1 meets the aforementioned requirements and exhibits a negative correlation with the fluctuation of the secondary ripple instantaneous value S1. More specifically, the following principles apply to determining the secondary ripple inverse proportionality coefficient D1: when S1 is maximum, D1 is minimum; when S1 is minimum, D1 is maximum; the value 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, exhibiting a negative correlation.

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

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

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

[0171] In actual train applications, when heavily loaded trains operate in difficult sections, the terminal voltage is low due to the long power supply arm, making it difficult for the train to pass. However, the terminal voltage boosting solution provided in this embodiment can control trains in some sections to stop traction and enter a stationary pantograph-raised state. A DC voltage is then established between the energy storage device and its DC converter. The four-quadrant converter then operates in inverter mode and delivers capacitive reactive power to the grid to compensate for the inductive reactive power in the line, thereby boosting the terminal voltage and facilitating the normal passage of other trains.

[0172] This demonstrates that this embodiment, based on the onboard energy storage system deployed in trains, can also be used to boost the voltage at the end of the grid. For example, when a train is at the end of a power supply arm, low grid voltage can affect train operation. In such cases, this embodiment can be used to stop traction on some trains using this solution and control them to raise their pantographs in a static manner. This changes their operating mode to that of a capacitive reactive generator, delivering capacitive reactive power to the grid. This in turn boosts the voltage at the end of the power supply arm, supporting the smooth passage of the remaining trains.

[0173] On the other hand, in addition to the above-mentioned secondary pulsation suppression and terminal voltage increase solutions, other functions can be achieved based on the configuration of the on-board energy storage system. This embodiment provides a possible implementation scheme, and the above-mentioned method also includes:

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

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

[0176] In actual train applications, when a train enters certain sections during winter, icing of the power grid may prevent the train from passing. In this case, the solution provided in this embodiment can utilize the onboard energy storage system deployed in the train to raise the pantograph when the train is stationary and inject inductive or capacitive reactive power into the power grid, causing the power grid cables to heat up and melt the ice, thereby allowing the train to exit the icy section.

[0177] In other words, this embodiment uses the output of the energy storage device to transmit capacitive or inductive reactive power to the grid, causing the grid to heat up and melt ice, achieving the AC ice-melting effect. Once the grid ice condition is improved, the train can smoothly pass through the iced section.

[0178] Furthermore, the AC ice melting solution provided in the above embodiment is not limited to a single vehicle or multiple vehicles. A single vehicle can be implemented using the above steps S51 and S52. For AC ice melting between multiple vehicles, this embodiment provides a further implementation scheme, and the above step S52 is specifically as follows:

[0179] The first part of the train is controlled to transmit capacitive reactive power to the power grid, and the second part of the train is controlled to transmit inductive reactive power to the power grid.

[0180] The sum of the capacitive reactive power delivered to the grid by the first part of the trains is equal to the sum of the inductive reactive power delivered to the grid by the second part of the trains.

[0181] For example, if two trains are separated by a certain distance, with one train supplying inductive reactive power to the grid and the other supplying an equal amount of capacitive reactive power, a reactive current path will be created between the two trains, eliminating the need to draw reactive current from a substation and enabling the specialized needs of short-distance ice melting. The same principle applies when there are more than two trains. As long as the total amount of capacitive reactive power injected into the grid is equal to the inductive reactive power, the AC ice melting function can be achieved while avoiding the other impacts of inductive or capacitive reactive power injected into the grid.

[0182] On the other hand, in addition to the aforementioned secondary pulsation suppression, terminal voltage boost, and AC ice melting solutions, other functions can also be achieved based on the configuration of the on-board energy storage system. This embodiment provides a possible implementation scheme, and the above method also includes:

[0183] S61: When the train is over-phased, the energy storage device is controlled by the DC converter to supply power to the train's load.

[0184] That is, this embodiment provides a non-stop solution for when a train passes through a phase separation. When the train is in the phase separation section, the power grid is in a power-off state. At this time, the four-quadrant converter stops working. This embodiment uses an energy storage device and a DC conversion system, and the energy storage system DC conversion stabilizes the intermediate DC voltage to power the traction inverter and the auxiliary inverter, thereby achieving non-stop traction and auxiliary operations. Therefore, the non-stop solution for passing through a phase separation provided by this embodiment prevents the train from stopping in a power-off zone due to a phase separation failure, resulting in a rescue accident, and does not cause auxiliary systems such as lighting and air-conditioning equipment to stop working, affecting the riding experience, thereby achieving more excellent performance.

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

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

[0187] In other words, this embodiment provides an emergency traction function based on the onboard energy storage system. In the event of a power outage or on non-electrified railway sections, the onboard energy storage system can provide emergency traction, thereby preventing the train from stopping in a power-off zone and potentially causing rescue accidents. It also prevents auxiliary systems such as lighting and air conditioning from shutting down and affecting the passenger experience, thus meeting special needs.

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

[0189] S63: When the power grid cannot independently bear the load of the train, the energy storage device is controlled by the DC converter to input power support into the DC bus, and the power grid is used to supply power to the train load.

[0190] In other words, this embodiment provides a hybrid traction function based on the onboard energy storage system. Under extreme line conditions, such as heavy-load traction on steep slopes, a hybrid traction mode combining the grid and the onboard energy storage system can be used to increase the overall traction power of the train and meet the traction needs under extremely heavy load conditions.

[0191] The above is a detailed introduction to a vehicle-mounted energy storage system and a control method based on the vehicle-mounted energy storage system provided by the present application. The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the various embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of this application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of this application.

[0192] It should also be noted that, in this specification, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

Claims

1. A vehicle-mounted energy storage system, characterized in that: include: Energy storage device, DC converter and 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 to: if the train is in a light-load condition, control 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, use the output target value of the energy storage device as a given quantity and the actual output value of the energy storage device as a feedback quantity, and control the output of the energy storage device by the DC converter through a closed-loop regulator; determine 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 the step of using the output target value of the energy storage device as a given quantity and the actual output value of the energy storage device as feedback quantity, and control the output of the energy storage device by the DC converter through a closed-loop regulator; The method for determining the output target value of the energy storage device includes: Obtaining an average 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; An output target value of the energy storage device is determined according to the output power target value.

2. A control method based on a vehicle-mounted energy storage system, characterized in that: Applied to the vehicle-mounted energy storage system according to claim 1, the method comprises: Obtaining the current load condition of the train; wherein the load condition includes: a light load condition and a non-light load condition; If the load condition is a light load condition, the four-quadrant converter in the train traction system is controlled to stop working, and the DC converter is controlled to enable the energy storage device to independently supply power to the load of the train; If the load condition is a non-light load condition, then when low-frequency oscillation occurs in the train, the output target value of the energy storage device is used as a given quantity and the actual output value of the energy storage device is used as a feedback quantity, and the DC converter controls the output of the energy storage device through a closed-loop regulator; determines whether the low-frequency oscillation of the train still exists; if so, increases the suppression coefficient to re-determine the output target value of the energy storage device, and returns to the step of using the output target value of the energy storage device as a given quantity and the actual output value of the energy storage device as a feedback quantity, and the DC converter controls the output of the energy storage device through a closed-loop regulator; The method for determining the output target value of the energy storage device includes: Obtaining an average 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; An output target value of the energy storage device is determined according to the output power target value.

3. The control method based on the vehicle-mounted energy storage system according to claim 2, characterized in that: Also includes: If the train still has low-frequency oscillations when the suppression coefficient is increased to 1, the traction power of the train is gradually reduced until the low-frequency oscillations of the train are eliminated.

4. The control method based on the vehicle-mounted energy storage system according to claim 2 or 3, characterized in that: Also includes: Acquiring an instantaneous value of a DC voltage, and extracting an instantaneous value of a secondary ripple from the instantaneous value of the DC voltage; Determining a secondary ripple amplitude and a secondary ripple inverse proportionality coefficient according to the secondary ripple instantaneous value; wherein the secondary ripple inverse proportionality coefficient is negatively correlated with the secondary ripple amplitude; controlling the output of the energy storage device through a secondary pulsation suppression strategy; The secondary pulsation suppression strategy is a dual 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 set value as the outer loop set 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 outer loop output and the secondary ripple inverse proportional coefficient as the inner loop set quantity, and the actual output value of the energy storage device as the inner loop feedback quantity.

5. The control method based on the vehicle-mounted energy storage system according to claim 4, characterized in that: Determining the secondary ripple inverse proportional coefficient according to the secondary ripple instantaneous value includes: Get the historical fluctuation range of the secondary ripple; Determine a first quantile position of the instantaneous value of the secondary ripple within the historical fluctuation range of the secondary ripple; determining a second quantile position based on a complementary mapping of the first quantile position; Based on the second quantile position, determining a corresponding value from a preset inverse proportional coefficient value interval as the secondary ripple inverse proportional coefficient; The median value of the inverse proportional coefficient value interval is 1.

6. The control method based on the vehicle-mounted energy storage system according to claim 2 or 3, characterized in that: Also includes: Controlling the train to stop traction and enter a stationary pantograph raising state; The output of the energy storage device is controlled by the DC converter to establish a DC bus voltage, and the four-quadrant converter is controlled to operate in an inverter mode to deliver capacitive reactive power to the power grid.

7. The control method based on the vehicle-mounted energy storage system according to claim 2 or 3, characterized in that: Also includes: Controlling the train to stop traction and enter a stationary pantograph raising state; The output of the energy storage device is controlled by the DC converter to establish a DC bus voltage, and the four-quadrant converter is controlled to operate in an inverter mode to deliver capacitive reactive power or inductive reactive power to the power grid.

8. The control method based on the vehicle-mounted energy storage system according to claim 7, characterized in that: The train is a plurality of trains; Then, controlling the four-quadrant converter to operate in an inverter mode to transmit capacitive reactive power or inductive reactive power to the power grid includes: Controlling the train in the first part to deliver capacitive reactive power to the power grid, and controlling the train in the second part to deliver inductive reactive power to the power grid; The sum of the capacitive reactive power delivered to the power grid by the trains in the first part is equal to the sum of the inductive reactive power delivered to the power grid by the trains in the second part.

9. The control method based on the vehicle-mounted energy storage system according to claim 2 or 3, characterized in that: Also includes: If the output power of the four-quadrant converter still has residual capacity after bearing the load of the train, the four-quadrant converter is controlled to output at rated power, and the energy storage device is controlled to operate in a charging mode through the DC converter.

10. The control method based on the vehicle-mounted energy storage system according to claim 2 or 3, characterized in that: Also includes: If the traction motor in the train operates in a braking mode, the traction inverter is controlled to operate in a braking state, and the energy storage device is controlled to operate in a charging mode through the DC converter.

11. The control method based on the vehicle-mounted energy storage system according to claim 2 or 3, characterized in that: Also includes: When the train is over-phased, the energy storage device is controlled by the DC converter to supply power to the load of the train.

12. The control method based on the vehicle-mounted energy storage system according to claim 2 or 3, characterized in that: Also includes: When the power grid loses power or the train runs in a non-electrified railway section, the energy storage device is controlled by the DC converter to supply power to the load of the train.

13. The control method based on the vehicle-mounted energy storage system according to claim 2 or 3, characterized in that: Also includes: When the power grid cannot independently bear the load of the train, the DC converter controls the energy storage device to input power support into the DC bus, and the power grid and the energy storage device jointly supply power to the load of the train.

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