Hybrid energy storage system for high-power repetitive pulse load and optimization method thereof

Abstract

The application discloses a hybrid energy storage system for a high-power heavy-frequency pulse load and an optimization method thereof, the hybrid energy storage system comprising a lithium ion battery, a super capacitor and a DC / DC converter; the super capacitor is connected between positive and negative DC buses of the high-power heavy-frequency pulse load, and the lithium ion battery is connected between the positive and negative DC buses of the high-power heavy-frequency pulse load through the DC / DC converter. The application is applied to the fields of new energy storage and new energy electric vehicles, and can effectively realize modeling of the hybrid energy storage system for a high-power short-time pulse working condition, optimal design of a hybrid energy storage system integration scheme for a miniaturization target, and the hybrid energy storage system designed based on the technology has the advantages of miniaturization and a wide temperature range, and has a wide application prospect in a wide temperature range heavy-frequency pulse working condition scene.

Description

Technical Field

[0001] This invention relates to the fields of novel energy storage and new energy electric vehicles, specifically a lithium-ion battery-supercapacitor hybrid energy storage system and its optimization method for high-power high-repetition-rate pulse loads. Background Technology

[0002] A hybrid energy storage system (HESS) is a system that combines multiple energy storage technologies to fully leverage the advantages of each technology while compensating for the shortcomings of a single technology. Common combinations in hybrid energy storage systems include batteries and supercapacitors. Batteries (such as lithium-ion batteries) offer high energy density, suitable for long-term energy storage, while supercapacitors provide high power density, suitable for rapid charging and discharging, and handling high load demands for short periods. By combining these two technologies, hybrid energy storage systems can provide smoother and more efficient energy management, adapting to varying loads and power supply conditions.

[0003] There are many ways to connect lithium-ion batteries and supercapacitors. Currently, the hybrid energy storage systems (HESS) composed of them are mainly divided into two categories: passive hybrid energy storage systems and active hybrid energy storage systems.

[0004] Passive hybrid energy storage systems are systems composed of lithium-ion batteries and supercapacitors connected in parallel or through passive devices (diodes, inductors, etc.). They have a simple structure and do not require additional control components to control the charging and discharging of the energy storage device.

[0005] Unlike passive hybrid energy storage systems, active hybrid energy storage systems incorporate a power converter (DC / DC converter). This allows for flexible control and allocation of the energy storage device's charging and discharging power, fully leveraging the hybrid system's advantages in handling pulsed operating conditions. Based on the number and location of the power converters, active hybrid energy storage systems primarily have series, parallel, multi-input converter, and single-converter structures.

[0006] refer to Figure 1 (a) Figure 1 (b) In the series-connected active hybrid energy storage system topology, a DC / DC converter is first used to decouple the DC bus from the supercapacitor and battery. Then, the supercapacitor subsystem and the battery subsystem are connected in parallel through a DC / DC converter. (Comparison) Figure 1 (a) Figure 1 (b) As can be seen from the two series topologies, when the battery is used as the main energy source in the hybrid energy storage system, the connection method in 1(a) reduces the system efficiency to some extent. Furthermore, due to the large voltage variation of the supercapacitor pack, the use of... Figure 1(b) connection method makes it easier to maintain the stability of the voltage at both ends of the battery and the DC bus voltage.

[0007] refer to Figure 1 (c) In a parallel active hybrid energy storage system topology, the battery and supercapacitor are connected to the DC bus via DC / DC converters. This connection method allows energy transfer between the battery and the DC bus to be achieved through only one DC / DC converter for both the battery and the supercapacitor, making it more efficient than a series topology.

[0008] refer to Figure 1 (d) In the active hybrid energy storage system topology with a multi-input converter structure, the battery and supercapacitor are decoupled from the DC bus through a multi-input DC / DC converter to achieve power distribution between them. Compared with the parallel topology, the multi-input converter topology has improved system integration and certain advantages in terms of weight and volume, but it is not as flexible in system layout as the parallel topology and has higher control complexity.

[0009] refer to Figure 1 (e) Figure 1 (f) In the active hybrid energy storage system topology with a single converter structure (single converter type structure), one of the lithium battery subsystem and the supercapacitor subsystem is decoupled from the DC bus through a DC / DC converter. This can also achieve power distribution between the two subsystems, but the bus voltage is no longer controllable. Figure 1 The biggest advantage of the single-converter topology shown in (e) is the relatively stable bus voltage (the voltage-SOC curve of the battery is relatively flat in the middle, and the voltage drop is not fast), which is very important for certain specific applications. However, the biggest problem with this system is that under pulsed conditions, a large pulse power should be output by the supercapacitor, which leads to a relatively high DC / DC power demand. Therefore, its size, weight, and price are also higher, and the system efficiency will also be affected to some extent. Figure 1 The single converter topology shown in (f) connects the DC / DC converter to the battery terminal. The advantage of this is that it can reduce the operating power required by the DC / DC converter, thereby reducing the system size, weight and cost, and improving system efficiency. However, its main disadvantage is that the bus voltage may fluctuate significantly with the change of the supercapacitor voltage. Therefore, accurate modeling and optimization design are required to meet the voltage requirements of practical applications. Summary of the Invention

[0010] To address the shortcomings of the existing technologies, this invention provides a lithium-ion battery-supercapacitor hybrid energy storage system and its optimization method for high-power high-repetition-rate pulse loads. It can effectively realize the modeling of hybrid energy storage systems for high-power short-time pulse conditions and the optimal design of hybrid energy storage system integration schemes for miniaturization. The resulting hybrid energy storage scheme has the advantages of miniaturization and wide temperature range, and has broad application prospects in wide temperature range high-repetition-rate pulse conditions.

[0011] To achieve the above objectives, the present invention provides a hybrid energy storage system for high-power high-repetition-rate pulse loads, comprising a lithium-ion battery, a supercapacitor, and a DC / DC converter;

[0012] The supercapacitor is connected between the positive and negative DC buses of the high-power high-repetition-rate pulse load, and the lithium-ion battery is connected between the positive and negative DC buses of the high-power high-repetition-rate pulse load through the DC / DC converter.

[0013] To achieve the above objectives, the present invention also provides an optimization method for the hybrid energy storage system for high-power high-repetition-rate pulse loads, comprising the following steps:

[0014] High-rate pulse discharge and pulse aging tests were conducted on the candidate lithium battery cells and supercapacitor cells in the design of hybrid energy storage systems.

[0015] Based on the data obtained from high-rate pulse discharge test and pulse aging test, and based on the equivalent circuit model, Arrhenius model and damage accumulation theory, the dynamic response characteristics of lithium battery cells and supercapacitor cells and the aging characteristics of lithium battery cells are modeled respectively.

[0016] Based on the single-cell model, the aging of the entire hybrid energy storage system is characterized by the aging degree of lithium batteries. According to the topology of the hybrid energy storage system, a mathematical model of the active structure hybrid energy storage system is constructed.

[0017] Based on the mathematical model of the active structure hybrid energy storage system, the active structure hybrid energy storage system is optimized with minimizing the mass of the hybrid energy storage system as the optimization objective and the minimum operating temperature of the hybrid energy storage system as the constraint.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects:

[0019] 1. This invention relates to a hybrid energy storage system for high-power, high-repetition-rate (PRR) pulse loads. A supercapacitor is directly connected between the positive and negative DC buses of the high-power, high-repetition-rate (PRR) pulse load, while a lithium-ion battery is connected between the positive and negative DC buses of the high-power, high-repetition-rate (PRR) pulse load via a DC / DC converter. The main idea is to use the supercapacitor to handle peak power output, while the lithium-ion battery handles average power output (controlled by the DC / DC converter). Therefore, connecting the DC / DC converter to the battery terminal during pulsed conditions effectively reduces the operating power of the DC / DC converter (average power is often much lower than peak power under pulsed conditions), which is beneficial for the miniaturization of the hybrid energy storage system. Furthermore, the use of the DC / DC converter makes the battery output voltage and current controllable. In low-temperature environments, the battery output power can be increased by reducing the lithium battery voltage. Moreover, the capacitor bank voltage is no longer clamped by the battery bank, allowing full utilization of the allowable bus voltage fluctuation range for each pulsed discharge. The capacity and power capability of the supercapacitor can also be more fully utilized.

[0020] 2. In this invention, the single-converter topology is applied under high-power high-repetition-rate pulses, which can significantly improve the miniaturization level and wide-temperature performance of the entire hybrid energy storage system, and minimize the output power requirements of the DC / DC converter.

[0021] 3. The optimization method in this invention, in the process of optimizing the hybrid energy storage system with high power repetition frequency pulse load, starts from the actual requirements of high power repetition frequency pulse operating conditions and considers the two mutually restrictive indicators of system quality and minimum operating temperature, so that the hybrid energy storage system can have both miniaturization and wide temperature range characteristics.

[0022] 4. In the optimization method of the present invention, starting from the testing and modeling of individual battery and capacitor cells in the hybrid energy storage system, the wide-temperature-range pulse dynamic response characteristics modeling of the active structure hybrid energy storage system is gradually completed, filling the research gap in the current research on the dynamic response modeling of hybrid energy storage under wide-temperature-range and pulsed operating conditions. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0024] Figure 1The diagrams show active hybrid energy storage systems with different structures, where: (a) and (b) are topological diagrams of active hybrid energy storage systems with series structure, (c) is a topological diagram of active hybrid energy storage systems with parallel structure, (d) is a topological diagram of active hybrid energy storage systems with multi-input converter structure, and (e) and (f) are topological diagrams of active hybrid energy storage systems with single converter structure.

[0025] Figure 2 This is a schematic diagram of a hybrid energy storage system for high-power high-repetition-rate pulse loads in an embodiment of the present invention;

[0026] Figure 3 This is an optimization flowchart of a hybrid energy storage system for high-power high-repetition-rate pulse loads in an embodiment of the present invention;

[0027] Figure 4 This is a schematic diagram of the OCV-SOC fitting curves of the AHP8AU1 lithium iron phosphate battery at different temperatures in an embodiment of the present invention;

[0028] Figure 5 The following are schematic diagrams of the test results of the AHP8AU1 lithium iron phosphate battery under high-rate pulse discharge at different temperatures in the embodiments of the present invention: (a) is a schematic diagram of the test results at -20℃, (b) is a schematic diagram of the test results at 0℃, and (c) is a schematic diagram of the test results at 20℃.

[0029] Figure 6 for Figure 5 A schematic diagram of the voltage waveform in the middle stage of a medium-pulse discharge, wherein: (a) is a schematic diagram at -20℃, (b) is a schematic diagram at 0℃, and (c) is a schematic diagram at 20℃;

[0030] Figure 7 The following are schematic diagrams of the test results of the TPEH-180 supercapacitor under high-rate pulse discharge at different temperatures in the embodiments of the present invention: (a) is a schematic diagram of the test results at -20℃, (b) is a schematic diagram of the test results at 0℃, and (c) is a schematic diagram of the test results at 20℃.

[0031] Figure 8 The following are schematic diagrams of the test results of the TPEH-400 supercapacitor under high-rate pulse discharge at different temperatures in the embodiments of the present invention: (a) is a schematic diagram of the test results at -20℃, (b) is a schematic diagram of the test results at 0℃, and (c) is a schematic diagram of the test results at 20℃.

[0032] Figure 9 The diagram shows a first-order RC equivalent circuit model in an embodiment of the present invention, wherein: (a) is a first-order RC equivalent circuit model of a lithium iron phosphate battery, and (b) is a first-order RC equivalent circuit model of a supercapacitor.

[0033] Figure 10 This is a schematic diagram of the Rint model in an embodiment of the present invention, wherein: (a) is a schematic diagram of the Rint model of a lithium iron phosphate battery, and (b) is a schematic diagram of the Rint model of a supercapacitor;

[0034] Figure 11 The following is a schematic diagram of the 0.1s internal resistance of the candidate cells in the embodiments of the present invention, wherein: (a) is a schematic diagram of the 0.1s internal resistance of the lithium iron phosphate battery cell, (b) is a schematic diagram of the 0.1s internal resistance of the TPEH-400 supercapacitor cell, and (c) is a schematic diagram of the 0.1s internal resistance of the TPEH-400 supercapacitor cell.

[0035] Figure 12 This is a flowchart illustrating the joint optimization of the active structure hybrid energy storage system in an embodiment of the present invention.

[0036] Figure 13 This is a schematic diagram illustrating a high-power high-repetition-rate pulse operating condition as exemplified in an embodiment of the present invention;

[0037] Figure 14 This is a schematic diagram of the bus voltage response during the pulse discharge process of the active hybrid energy storage system at -20℃ in an embodiment of the present invention, wherein: (a) is a schematic diagram of the bus voltage response after 2000 pulse discharges at -20℃, and (b) is a schematic diagram of 20 pulse waveforms starting from the 60th second in the 2000 pulse discharges.

[0038] Figure 15 This is a schematic diagram of the battery pack terminal voltage curve during the pulse discharge process of the active hybrid energy storage system at -20℃ in an embodiment of the present invention, wherein: (a) is a schematic diagram of the battery pack terminal voltage during the pulse discharge process, and (b) is a schematic diagram of the 20 pulse waveforms starting from the 60th second;

[0039] Figure 16 This is a schematic diagram comparing the output current of the lithium iron phosphate battery pack and the supercapacitor pack during pulse discharge at -20℃ in an embodiment of the present invention. (a) is a schematic diagram comparing the output current of the lithium iron phosphate battery pack and the supercapacitor pack during pulse discharge, and (b) is a schematic diagram of the current distribution of the 20 pulses starting from the 60th second.

[0040] Figure 17 This is a schematic diagram of the bus voltage response during the pulse discharge process of the active hybrid energy storage system at 20°C in an embodiment of the present invention, wherein: (a) is a schematic diagram of the bus voltage response after 2000 pulse discharges at 20°C, and (b) is a schematic diagram of 20 pulse waveforms starting from the 60th second of the 2000 pulse discharges.

[0041] Figure 18This is a schematic diagram of the battery pack terminal voltage curve during the pulse discharge process of the active hybrid energy storage system at 20°C in an embodiment of the present invention, wherein: (a) is a schematic diagram of the battery pack terminal voltage during the pulse discharge process, and (b) is a schematic diagram of the 20 pulse waveforms starting from the 60th second;

[0042] Figure 19 This is a schematic diagram comparing the output current of the lithium iron phosphate battery pack and the supercapacitor pack during pulse discharge at 20°C in an embodiment of the present invention. (a) is a schematic diagram comparing the output current of the lithium iron phosphate battery pack and the supercapacitor pack during pulse discharge, and (b) is a schematic diagram of the current distribution of the 20 pulses starting from the 60th second.

[0043] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0045] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0046] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0047] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection, an electrical connection, a physical connection, or a wireless communication connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two elements or the interaction between two elements, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0048] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0049] This embodiment discloses a hybrid energy storage system for high-power high-repetition-rate (PRR) pulse loads, primarily applicable to high-power PRR pulse conditions, such as power frequency regulation and radar systems. (Reference) Figure 2 This hybrid energy storage system comprises a lithium-ion battery, a supercapacitor, and a DC / DC converter. The supercapacitor is connected between the positive and negative DC buses of the high-power, high-repetition-rate (PRR) pulse load, while the lithium-ion battery is connected between the positive and negative DC buses of the high-power, high-repetition-rate (PRR) pulse load via the DC / DC converter. The DC / DC converter primarily decouples the lithium-ion battery and supercapacitor, achieving precise power distribution through control of the current and voltage in the lithium-ion battery and supercapacitor branches within the system.

[0050] In this embodiment, the hybrid energy storage system directly connects a supercapacitor between the positive and negative DC buses of a high-power, high-repetition-rate (PRR) pulse load, while simultaneously connecting a lithium-ion battery between the positive and negative DC buses of the load via a DC / DC converter. The main idea is to use the supercapacitor to primarily handle peak power output, while the lithium-ion battery primarily handles average power output (controlled by the DC / DC converter). Therefore, connecting the DC / DC converter to the battery terminal during pulsed conditions effectively reduces the DC / DC converter's operating power (average power is often much lower than peak power under pulsed conditions), facilitating the miniaturization of the hybrid energy storage system. Furthermore, the use of the DC / DC converter makes the battery's output voltage and current controllable. In low-temperature environments, the battery output power can be increased by reducing the lithium battery voltage. Moreover, the capacitor bank voltage is no longer constrained by the battery bank, allowing full utilization of the allowable bus voltage fluctuation range during each pulse discharge. The capacity and power capability of the supercapacitor can also be more fully utilized.

[0051] This embodiment also discloses a... Figure 2 An optimization method for hybrid energy storage systems designed for high-power, high-repetition-rate pulse loads, referenced in [reference]. Figure 3 It includes the following steps:

[0052] First, high-rate pulse discharge tests and pulse aging tests were conducted on the candidate lithium battery cells and supercapacitor cells in the design of the hybrid energy storage system.

[0053] Secondly, based on the data obtained from high-rate pulse discharge test and pulse aging test, and based on the equivalent circuit model, Arrhenius model and damage accumulation theory, the dynamic response characteristics of lithium battery cells and supercapacitor cells and the aging characteristics of lithium battery cells are modeled respectively.

[0054] Then, based on the single-cell model, the aging of the entire hybrid energy storage system is characterized by the degree of lithium battery aging. According to the topology of the hybrid energy storage system, a mathematical model of the active structure hybrid energy storage system is constructed.

[0055] Finally, based on the mathematical model of the active structure hybrid energy storage system, the active structure hybrid energy storage system is optimized with minimizing the mass of the hybrid energy storage system as the optimization objective and the minimum operating temperature of the hybrid energy storage system as the constraint.

[0056] In this embodiment, an 8Ah square soft-pack lithium iron phosphate battery cell, a 180F 3.0V supercapacitor cell, and a 400F 3.0V supercapacitor cell are used as examples, and their main parameters are shown in Table 1.

[0057] Table 1

[0058]

[0059] The AHP8AU1 lithium iron phosphate battery underwent OCV-SOC curve testing, high-rate pulse discharge testing, and pulse cycle aging testing at different temperatures. The OCV-SOC data of the lithium iron phosphate battery at different temperatures are shown in Table 2.

[0060] Table 2

[0061]

[0062] By fitting the data in Table 2, we can obtain the OCV-SOC fitting curves of the AHP8AU1 lithium iron phosphate battery at different temperatures, i.e. Figure 4 As shown. According to Figure 4 It is evident that temperature has a negligible impact on the open-circuit voltage of lithium iron phosphate batteries. Furthermore, the OCV-SOC curve fitted based on 11 data points meets the optimization requirements of the hybrid energy storage system in this embodiment; however, its accuracy is generally poor in the range above 90% SOC and below 10% SOC. Therefore, a low-current quasi-steady-state charge-discharge test was first conducted at 20 degrees Celsius to obtain a more accurate OCV-SOC curve. Considering the minimal impact of temperature on the open-circuit voltage of lithium iron phosphate batteries, the curve obtained from the quasi-steady-state test can be directly applied to low-temperature scenarios when needed.

[0063] The test results of high-rate pulse discharge tests on AHP8AU1 lithium iron phosphate batteries at different temperatures are as follows: Figure 5 As shown, Figure 5 (a) Figure 5 (b) Figure 5 (c) shows the test data at -20, 0, and 20 degrees Celsius. It can be seen that at -20 degrees Celsius, due to the battery's temperature rise during pulse discharge, the set 200 pulses with a 1s pulse width and a 1 / 6 duty cycle of a 12.5C square wave pulse are insufficient to discharge the battery to the lower cutoff voltage. Therefore, the pulse number limit was relaxed in the tests at 0 degrees Celsius and 20 degrees Celsius. At 0 degrees Celsius and 20 degrees Celsius, the battery discharged to the lower cutoff voltage after 326 and 329 pulses, respectively. Figure 6 (a) Figure 6 (b) Figure 6 (c) respectively with Figure 5 (a) Figure 5 (b) Figure 5 (c) Correspondingly, the voltage waveform in the middle of the pulse discharge is displayed.

[0064] In this hybrid energy storage system, the supercapacitor is primarily used to absorb the instantaneous power surges of high-power pulses. During the pulse discharge cycle, the supercapacitor remains in a high-voltage range above 85% of its rated voltage. Due to the short discharge cycle, leakage current is not a concern during continuous pulses; the operating voltage range is narrow, so the changes in the supercapacitor's capacitance and internal resistance with voltage are not considered during charging and discharging. Therefore, under the target operating conditions in this embodiment, the open-circuit voltage of the supercapacitor conforms to the ideal capacitor voltage formula, which is:

[0065]

[0066] Among them, U sc Q is the open-circuit voltage of the supercapacitor. SC For the amount of charge carried by a supercapacitor, C SC This represents the capacitance value of the supercapacitor.

[0067] By conducting high-rate pulse discharge tests on supercapacitors at different temperatures, the internal resistance and capacitance values ​​required for modeling the dynamic characteristics of the supercapacitor can be obtained from the voltage and current data obtained from the tests. The results of high-rate pulse discharge tests on TPEH-180 and TPEH-400 supercapacitors at different temperatures in this embodiment are as follows: Figure 7 , Figure 8 As shown, where Figure 7 (a) Figure 7 (b) Figure 7 (c) and Figure 8 (a) Figure 8 (b) Figure 8(c) The test data are at -20, 0 and 20 degrees Celsius respectively. The first discharge pulse data in each temperature test will be taken to calculate the 0.1s internal resistance and average capacitance of this type of supercapacitor in the high voltage range at that temperature.

[0068] Based on the above test results, dynamic response characteristics of individual lithium iron phosphate batteries and supercapacitors considering temperature effects were modeled, and pulse cycle aging characteristics of lithium iron phosphate batteries were modeled based on the Arrhenius decay model. Since the target operating condition in this embodiment involves a single discharge pulse within the second range, considering the accuracy and calibration complexity of various equivalent circuit models at this time scale, this embodiment initially chose to use a first-order RC model for model parameter identification under pulse operating conditions for lithium iron phosphate batteries and supercapacitors. (Reference) Figure 9 The first-order RC equivalent circuit model consists of the equivalent series resistance R0 and the equivalent parallel resistance R. p and parallel capacitor C p The composition, also known as the classical equivalent circuit model or Thevinin equivalent circuit model, is characterized by a device voltage source.

[0069] The state-space equation of the first-order RC equivalent circuit model of a lithium iron phosphate battery is:

[0070]

[0071] Among them, U Bat I is the battery terminal voltage. Bat The battery current (output is negative), V Bat Battery open-circuit voltage;

[0072] The state-space equation of the first-order RC equivalent circuit model of a supercapacitor is:

[0073]

[0074] Among them, U SC I is the terminal voltage of the supercapacitor. SC For the supercapacitor current (output is negative), V SC This is the open-circuit voltage of the supercapacitor;

[0075] Parameter identification was performed on the first-order RC equivalent circuit models of the candidate lithium batteries and supercapacitors. Simulation verification revealed that the identified RC loop time constant was at least on the order of several seconds, and its impact on the model's dynamic characteristics was negligible for the pulse discharge conditions within seconds in this embodiment. Meanwhile, the ohmic internal resistance of the device significantly affects its dynamic response characteristics with temperature variations. Therefore, to accurately reflect the dynamic performance of the device under the target operating conditions while minimizing computational complexity, the first-order RC model used in this embodiment is simplified as follows: Figure 10 The Rint model is shown, and the variation of ohmic internal resistance with device temperature is further considered.

[0076] against Figure 10 The Rint model, considering the temperature effect, was used to conduct high-rate pulse discharge tests at different temperatures on the candidate AHP8AU1 lithium iron phosphate battery and TPEH-180 and TPEH-400 supercapacitors. The internal resistance was calculated for 0.1 seconds using the first discharge pulse after resting. The test results are shown below. Figure 11 As shown.

[0077] according to Figure 11 The test results show that:

[0078] AHP8AU1 lithium iron phosphate battery internal resistance R BAT With battery temperature T BAT The fitted curve of the change is:

[0079]

[0080] TPEH-180 supercapacitor internal resistance R SC1 With its temperature T SC1 The fitted curve of the change is:

[0081] R SC1 =0.000000851T BAT 2 -0.000038717T BAT +0.003858065

[0082] TPEH-400 supercapacitor internal resistance R SC2 With its temperature T SC2 The fitted curve of the change is:

[0083] R SC2 =0.000000266T BAT 2 -0.000010175T BAT +0.001658985

[0084] In addition to the internal resistance that varies with temperature, the Rint model also includes the open-circuit voltage parameter V. BAT and V SC For lithium batteries, the OCV-SOC curve and data showing the change of open-circuit voltage with SOC are shown below. Figure 4 As shown in Table 2, it will not be repeated here; the open-circuit voltage of the supercapacitor is calculated according to formula (1), and the capacitance value of the supercapacitor at different temperatures needs to be determined, as shown in Table 3.

[0085] Table 3

[0086] TPEH-180 TPEH-400 20℃ 208.106F 395.5768F 0℃ 197.3522F 396.8137F -20℃ 196.9729F 397.4853F

[0087] As shown in Table 3, the capacitance of supercapacitors decreases to some extent as the temperature decreases. This trend is more obvious in 180F cells, while the capacitance of 400F cells is less affected by temperature.

[0088] Based on the Rint model of lithium battery and supercapacitor considering the temperature effect in this embodiment, and taking into account the decoupling effect of the DC / DC converter in the topology, a mathematical model of the active structure hybrid energy storage system can be constructed as follows:

[0089] V Bat (t)=OCV Bat (t)-I BAT (t)R BAT (T) (4)

[0090] V SC (t)=OCV SC (t)-I SC (t)R SC (T) (5)

[0091] V DC,in (t)=SN BAT V Bat (t) (6)

[0092] I DC,in (t)=PN BAT I Bat (t) (7)

[0093]

[0094] I Load (t)=I DC,out (t)+PN SC I SC (t) (9)

[0095] V Load (t)=V DC,out (t)=SN SC VSC (t) (10)

[0096] Among them, V Bat (t), V SC (t) represents the terminal voltage of a single lithium-ion battery cell and a single supercapacitor cell at time t, respectively, and OCV Bat (t), OCV SC (t) represents the open-circuit voltage of a single lithium-ion battery cell and a single supercapacitor cell at time t, respectively. BAT (t), I SC (t) represents the current of a single lithium-ion battery cell and a single supercapacitor cell at time t, respectively. BAT (T), R SC (T) represent the ohmic internal resistance of the lithium-ion battery and the supercapacitor at operating temperature T, respectively. DC,in (t), V DC,out (t) represents the input voltage and output voltage of the DC / DC converter at time t, respectively, and SN BAT PN BAT These represent the number of batteries connected in series and the number of batteries connected in parallel within the battery pack, respectively. DC,ij (t), I DC,out (t) represent the input current and output current of the DC / DC converter at time t, respectively. Load (t), V Load (t) represents the load current and voltage at time t, respectively, and PN SC PN SC These represent the number of capacitors connected in series and the number of capacitors connected in parallel within the capacitor bank, respectively.

[0097] Based on the mathematical model of the active structure hybrid energy storage system, the joint optimization solution of the active structure hybrid energy storage system can be performed. The joint optimization of the active structure hybrid energy storage system needs to consider both capacity configuration optimization and energy management optimization. Capacity configuration optimization is to give the optimal selection of devices in the hybrid energy storage system and the number of series and parallel connections, while energy management is to optimally allocate the load demand power during the pulse discharge process between the lithium iron phosphate battery pack and the supercapacitor pack. Since the load target operating condition in this embodiment is a periodic pulse operating condition, that is, the demand power curve of each pulse discharge is fixed; then as long as the following two conditions are met, the power allocation of the hybrid energy storage system will be optimal no matter how many pulse discharge cycles are performed: (1) The hybrid energy storage system has a consistent initial state before the start of each pulse discharge cycle; (2) The power allocation scheme is optimal in the first pulse discharge cycle.

[0098] Regarding the initial state, for supercapacitor banks, it is sufficient to charge them to their rated voltage before the end of each pulse discharge cycle. Since the lithium iron phosphate battery pack in the hybrid energy storage system is the energy source, the continuous decline in SOC without energy replenishment will cause inconsistencies in the initial state before the start of each pulse discharge cycle. Therefore, for lithium iron phosphate batteries, the goal is to ensure they output the maximum power they can currently output during pulse discharge. Calculated by the following formula:

[0099]

[0100] in, This represents the lower limit of the lithium-ion battery terminal voltage at operating temperature T.

[0101] Because the OCV-SOC curve of lithium iron phosphate batteries is relatively complex, for 2000 pulse discharges as a whole, the lithium battery pack may not achieve optimal system performance at its maximum output power during pulse discharge. Therefore, the decision variables for the joint optimization problem of the active hybrid energy storage system need to include the ratio of the lithium battery pack's output power during pulse discharge to its current maximum output power. Furthermore, the joint optimization of the active hybrid energy storage system also requires the maximum power of the DC / DC converter as one of the decision variables. Therefore, in this embodiment, the supercapacitor type is the parameter to be optimized as part of the joint optimization of the active hybrid energy storage system. SC Number of supercapacitors in series (SN) SC The number of supercapacitors in parallel (PN) SC Number of lithium batteries in series (SN) BAT PN number of lithium batteries in parallel BAT The ratio of the output power of a lithium battery during pulse discharge to its current maximum output power. DC / DC converter rated power The specific optimization objectives are:

[0102]

[0103] M HESS =(M SC ·SN SC ·PN SC +M Bat ·SN Bat ·PN Bat ) / EFF itg +M DC (13)

[0104] Among them, F obj Let M be the objective function. HESS For the quality of hybrid energy storage systems, M is the lowest temperature at which a hybrid energy storage system can operate normally. SC M Bat M DC These represent the mass of a single supercapacitor cell, a single lithium-ion battery cell, and a DC / DC converter, respectively, and the EFF. itg To improve the integration efficiency of hybrid energy storage systems.

[0105] In this embodiment, under the condition of meeting the requirements of high-power high-repetition-rate pulse load, the hybrid energy storage system is charged to its rated voltage before performing the task, requiring continuous operation for at least 2000 pulses. Furthermore, the power loss caused by the DC / DC converter is not considered in the optimization process of this embodiment.

[0106] For the components of hybrid energy storage systems, lithium iron phosphate batteries and supercapacitors, their electrical performance at high temperatures is generally better than at room temperature. Therefore, the highest temperature at which a hybrid energy storage system can operate normally is... The temperature should be set to the maximum allowable temperature specified in the device datasheet, typically around 60°C. However, as the temperature drops from room temperature to -40°C, the internal resistance of the lithium iron phosphate battery increases exponentially, and the internal resistance of the supercapacitor also increases to some extent. This causes a significant decrease in the device's power capability at low temperatures compared to room temperature, and at even lower... More devices need to be connected in parallel to provide power, which will increase the mass M of the hybrid energy storage system. HESS The increase; Minimization and M HESS The minimization of these factors is mutually constrained, constituting a typical bi-objective optimization problem. The optimization process in this embodiment also needs to satisfy the following constraints:

[0107]

[0108]

[0109]

[0110]

[0111]

[0112]

[0113]

[0114]

[0115]

[0116]

[0117]

[0118] Among them, among them, The required number of pulse discharges after charging a hybrid energy storage system to its rated voltage, f Pulse I is the pulse frequency under load conditions. Pulse n represents the amplitude of the pulse current under load conditions. P W is the pulse count variable. Pulse For load conditions, pulse width These are the minimum operating voltage and the maximum operating voltage under load, respectively. These represent the lower and upper limits of the lithium-ion battery terminal voltage at operating temperature T, respectively. These are the lower and upper limits of the terminal voltage of the supercapacitor, respectively. These represent the minimum input voltage, maximum input voltage, minimum output voltage, and maximum output voltage of the DC / DC converter. These are the maximum input and output currents of the DC / DC converter, respectively. These are the charging and discharging current limits for lithium-ion batteries, respectively. These are the charging and discharging current limits for the supercapacitor, respectively.

[0119] In this embodiment, a multi-objective genetic algorithm is used to jointly optimize the active structure hybrid energy storage system, referring to... Figure 12 The specific implementation process is as follows:

[0120] Step 1: Obtain the population size M, the maximum number of evolutionary iterations ItMax, and the range of values ​​for the parameter to be optimized;

[0121] Step 2: Generate an initial population S1 based on the range of values ​​for the parameters to be optimized, and set the number of generations It = 1; S1

[0122] Step 3: Simulate each individual in population S1 and select individuals that meet the requirements of high-power high-repetition-rate pulse load as candidate individuals.

[0123] Step 4: Calculate the objective function of each candidate individual, add the candidate individual with the smallest objective function to population S2, and perform selection, crossover, and mutation operations on all candidate individuals before adding them to population S2, until the number of individuals in population S2 reaches M.

[0124] Step 5: Let It = It + 1, and determine whether It > ItMax is true.

[0125] If so, output the best individual in population S2 as the optimization result;

[0126] Otherwise, set S1 = S2 and return to step 3.

[0127] In the specific implementation of step 3 above, each individual in the population is simulated using a Simulink model. During the simulation, each individual is charged to its rated voltage before performing the task, enabling it to... If an individual completes the aforementioned 2000 pulse discharges, it is considered to be able to operate normally at that temperature, and thus it is considered a candidate individual. As for constructing a corresponding Simulink model based on the mathematical model of the active structure hybrid energy storage system in this embodiment, this is a conventional technique in the field, and therefore will not be elaborated upon in this embodiment.

[0128] It is worth noting that the joint optimization of active structure hybrid energy storage systems is not limited to multi-objective genetic algorithms; other multi-objective optimization algorithms, such as particle swarm optimization and multi-objective evolutionary algorithms, can also be used.

[0129] In practical applications, the minimum operating temperature requirements for hybrid energy storage systems fall into four categories: first, normal operation above -40℃; second, commercial energy storage systems typically require normal operation above -20℃; third, normal operation in general ambient temperatures, i.e., above 0℃; and fourth, normal operation only at ambient temperature and above. Therefore, the minimum operating temperature of a hybrid energy storage system can be discretized. Optimization of the active hybrid energy storage system can be performed at different minimum operating temperatures (e.g., -20℃, 0℃, 20℃) with the goal of minimizing system mass, resulting in a scatter plot showing the correlation between the minimum operating temperature and minimum mass of the active hybrid energy storage system.

[0130] The following section provides a further explanation of the hybrid energy storage system and its optimization method for high-power, high-repetition-rate pulse loads in this embodiment, using specific examples.

[0131] In this example, for Figure 13 The high-power high-repetition-rate pulse condition shown above uses the AHP8AU1 lithium iron phosphate battery, which has been tested and modeled above, and two supercapacitors, TPEH-180 and TPEH-400. The optimal supercapacitor selection, the series and parallel connection scheme of the lithium battery and the supercapacitor, the ratio of the output power of the lithium battery during pulse discharge to its current maximum output power, and the rated power of the DC / DC converter are obtained through optimization.

[0132] Taking a minimum operating temperature of -20℃ as an example, the optimization method of this embodiment is used to solve the joint optimization problem of capacity configuration and energy management of an active hybrid energy storage system by setting the population size to 50 and the maximum number of iterations to 100 in a multi-objective genetic algorithm. The optimal hybrid energy storage scheme at the minimum operating temperature of -20℃ is obtained. The bus voltage response of this optimal hybrid energy storage scheme after 2000 pulse discharges at -20℃ is as follows: Figure 14 As shown in (a). Figure 14 (b) Shows 20 pulse waveforms starting from the 60th second of 2000 pulse discharges. Since the supercapacitor bank is directly connected to the bus, its voltage waveform is consistent with the bus voltage; the battery bank terminal voltage during the pulse discharge process is as follows... Figure 15 As shown in (a). Figure 15 (b) Similarly, the waveforms of the 20 pulses starting at 60 seconds are shown in detail. The output current comparison between the lithium iron phosphate battery pack and the supercapacitor pack during pulse discharge is as follows: Figure 16 As shown in (a). Figure 16 (b) Similarly, the current distribution of the 20 pulses starting from the 60th second is shown in detail.

[0133] The performance of the optimal mixed-storage scheme was further verified at ambient temperature (20°C). The bus voltage response of the optimal mixed-storage scheme after 2000 pulse discharges at 20°C is as follows: Figure 17 As shown in (a). Figure 17 (b) Shows 20 pulse waveforms starting from the 60th second of 2000 pulse discharges. Since the supercapacitor bank is directly connected to the bus, its voltage waveform is consistent with the bus voltage; the battery bank terminal voltage during the pulse discharge process is as follows... Figure 18 As shown in (a). Figure 18 (b) Similarly, the waveforms of the 20 pulses starting at 60 seconds are shown in detail. The output current comparison between the lithium iron phosphate battery pack and the supercapacitor pack during pulse discharge is as follows: Figure 19 As shown in (a). Figure 19 (b) Similarly, the current distribution of the 20 pulses starting from the 60th second is shown in detail.

[0134] Depend on Figures 14 to 19 It can be seen that, under conditions as low as -20°C and during 2000 pulse discharge cycles, the optimal hybrid storage scheme maintains a stable load-side voltage as the battery pack's OCV continuously decreases, indicating that the DC / DC converter effectively stabilizes the load-side voltage; the battery-side voltage also remains within the allowable input voltage range of the DC / DC converter. Figure 16 It can be seen that the total current output of the hybrid energy storage system conforms to Figure 13 The pulsed load condition shown demonstrates that the supercapacitor can handle the majority of the power output during pulsed discharge, significantly reducing the impact of pulsed power on the lithium iron phosphate battery pack within the system. Compared to passive hybrid energy storage systems, the use of a DC / DC converter in an active hybrid energy storage system allows the supercapacitor pack to play a more significant role in "peak shaving and valley filling" of the load's pulsed power demand.

[0135] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. An optimization method for a hybrid energy storage system for high-power, high-repetition-rate pulse loads, characterized in that, The hybrid energy storage system includes a lithium-ion battery, a supercapacitor, and a DC / DC converter. The supercapacitor is connected between the positive and negative DC buses of the high-power high-repetition-rate pulse load, and the lithium-ion battery is connected between the positive and negative DC buses of the high-power high-repetition-rate pulse load through the DC / DC converter. The optimization method of the hybrid energy storage system includes the following steps: High-rate pulse discharge and pulse aging tests were conducted on the candidate lithium battery cells and supercapacitor cells in the design of hybrid energy storage systems. Based on the data obtained from high-rate pulse discharge test and pulse aging test, and based on the equivalent circuit model, Arrhenius model and damage accumulation theory, the dynamic response characteristics of lithium battery cells and supercapacitor cells and the aging characteristics of lithium battery cells are modeled respectively. Based on the single-cell model, the aging of the entire hybrid energy storage system is characterized by the aging degree of lithium batteries. According to the topology of the hybrid energy storage system, a mathematical model of the active structure hybrid energy storage system is constructed. Based on the mathematical model of the active structure hybrid energy storage system, the active structure hybrid energy storage system is optimized with minimizing the mass of the hybrid energy storage system as the optimization objective and the minimum operating temperature of the hybrid energy storage system as the constraint.

2. The optimization method according to claim 1, characterized in that, The mathematical model of the active structure hybrid energy storage system is as follows: in, , They are respectively The terminal voltage of each lithium-ion battery cell and supercapacitor cell at any given time. , They are respectively The open-circuit voltage of a single lithium-ion battery cell and a single supercapacitor cell at any given time. , They are respectively The current of each lithium-ion battery cell and supercapacitor cell at any given time. , Operating temperature The internal resistance of lithium-ion batteries and supercapacitors. , They are respectively The input voltage and output voltage of the DC / DC converter at any given time. , These represent the number of batteries connected in series and the number of batteries connected in parallel within the battery pack, respectively. , They are respectively The input current and output current of the DC / DC converter at any given time , They are respectively Load current and voltage at any given time , These represent the number of capacitors connected in series and the number of capacitors connected in parallel within the capacitor bank, respectively.

3. The optimization method according to claim 2, characterized in that, The specific optimization objective is as follows: in, Let be the objective function. For the quality of hybrid energy storage systems, This is the minimum temperature at which a hybrid energy storage system can operate normally. 、 、 These refer to the mass of a single supercapacitor cell, a single lithium-ion battery cell, and a DC / DC converter. To improve the integration efficiency of hybrid energy storage systems.

4. The optimization method according to claim 3, characterized in that, The joint optimization of the active structure hybrid energy storage system specifically involves: by , , 、 、 、 、 For the parameters to be optimized, a multi-objective genetic algorithm is used to jointly optimize the active structure hybrid energy storage system; in, This is the ratio of the output power of a lithium battery during pulse discharge to its current maximum output power. This refers to the model number of the supercapacitor. This refers to the rated power of the DC / DC converter.

5. The optimization method according to claim 4, characterized in that, The process of jointly optimizing the active structure hybrid energy storage system using a multi-objective genetic algorithm is as follows: Step 1, Obtain the population size Maximum number of evolution iterations The range of values ​​for the parameter to be optimized; Step 2: Generate an initial population based on the value range of the parameter to be optimized. And let the number of generations of evolution ; Step 3, for the population Each individual in the simulation is used to select the individual that meets the requirements of high-power high-repetition-rate pulse load as a candidate individual; Step 4: Calculate the objective function for each candidate individual, and add the candidate individual with the smallest objective function to the population. After performing selection, crossover, and mutation operations on all candidate individuals, they were added to the population. until the population The number of individuals reached ; Step 5, let and judge Is it true or false? If so, output population The best individual among them is taken as the optimization result; Otherwise, let Then return to step 3.

6. The optimization method according to claim 5, characterized in that, In step 3, during the population analysis... During the simulation of each individual entity, the following constraints must be satisfied: in, The required number of pulse discharges after charging a hybrid energy storage system to its rated voltage. The load operating pulse frequency, The amplitude of the pulse current under load conditions. For the number of pulses, The pulse width under load conditions; in, , These are the minimum operating voltage and the maximum operating voltage under load, respectively. , Operating temperature The lower and upper limits of the terminal voltage of lithium-ion batteries. , These are the lower and upper limits of the terminal voltage of the supercapacitor, respectively. , , , These represent the minimum input voltage, maximum input voltage, minimum output voltage, and maximum output voltage of the DC / DC converter, respectively. in, , These are the maximum input and output currents of the DC / DC converter, respectively. , These are the charging and discharging current limits for lithium-ion batteries, respectively. , These are the charging and discharging current limits for the supercapacitor, respectively.

7. The optimization method according to any one of claims 1 to 6, characterized in that, The minimum operating temperature of the hybrid energy storage system is discretized to obtain several different minimum operating temperatures. At each minimum operating temperature, the active structure hybrid energy storage system is optimized with the goal of minimizing the mass of the hybrid energy storage system. A scatter plot of the correlation between the minimum operating temperature and the minimum mass of the active structure hybrid energy storage system is obtained.

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