A distributed power management strategy for hybrid electric propulsion systems in electric aircraft

Abstract

This invention specifically relates to a distributed power management strategy for a hybrid electric propulsion system for electric aircraft, belonging to the field of aviation electrification. The system consists of a fuel cell, an energy storage battery, and a supercapacitor connected in parallel to a DC bus via a power converter. In this invention, each unit is independently controlled based on local information, eliminating the need for a communication network: the fuel cell adaptively switches between voltage and power modes according to the load power and battery state of charge, avoiding heavy or light load operation; the battery adjusts its steady-state operating point through a virtual resistance droop mechanism, absorbing steady-state power deficits or excess power; the supercapacitor absorbs dynamic power through a virtual capacitance droop mechanism, suppressing load fluctuations. This invention effectively suppresses the negative impacts of heavy / light loads, load fluctuations, and frequent start-stop cycles on fuel cell lifespan and efficiency, reduces hydrogen consumption, and improves overall system reliability.

Description

Technical Field

[0001] This invention relates to the field of aviation electrification, specifically to a distributed power management strategy in a hybrid electric propulsion system for an electric aircraft, which can effectively improve the overall energy conversion efficiency and reliability of the system, save hydrogen fuel consumption, and extend the system's service life. Background Technology

[0002] In recent years, to alleviate the global energy crisis, countries worldwide have been committed to the development of transportation electrification. Electric aircraft are a prime example, with their thrust and other power requirements provided by power supply units. Among various energy forms, proton exchange membrane fuel cells (PEMFCs) are widely used as power sources for electric propulsion aircraft due to their zero emissions, high efficiency, and quiet operation. Furthermore, to ensure optimal system performance, energy storage units such as batteries and supercapacitors are typically connected in parallel with fuel cells, forming a hybrid propulsion system. In electric aircraft propulsion systems, power management can optimize the distribution of electrical energy among heterogeneous power generation units such as fuel cells, energy storage batteries, and supercapacitors. This avoids the problems of low efficiency and reduced reliability of fuel cells under heavy load, light load, load fluctuations, and frequent start-stop conditions, as well as safety issues caused by overcharging and over-discharging of energy storage batteries. This effectively improves the overall energy conversion efficiency and operational reliability of the system, thereby saving hydrogen energy, extending the system's lifespan, and achieving economical, safe, and reliable operation of the hybrid electric propulsion system.

[0003] In existing power management strategies, centralized methods are widely used in hybrid electric propulsion systems. These methods use a central controller to monitor system operating status and manage power; however, due to their heavy reliance on the central controller and communication, single points of failure can affect their feasibility. Distributed power management methods remove the dependence on a central controller, but still require a communication network between distributed power sources for information exchange. Communication delays and potential data failures can hinder the response speed of the control algorithm and reduce system reliability.

[0004] Decentralized power management methods do not rely on communication, operating solely based on local information from each distributed unit, thus improving the reliability and flexibility of the power system. Currently, decentralized power management methods for hybrid electric propulsion systems are mainly divided into two categories: virtual impedance methods and inertia simulation methods. Virtual impedance methods achieve dynamic power management by introducing virtual impedances with different characteristics into each unit; inertia simulation methods use control algorithms to make the power electronic converter simulate the output characteristics of a DC motor to suppress voltage oscillations and adjust power management between parallel units. Overall, both control strategies can achieve dynamic power management, but they do not address steady-state power management.

[0005] The operating performance of a fuel cell is closely related to its actual operating conditions. In real-world operation, when a fuel cell operates under heavy load, its output power approaches its rated limit, accelerating membrane electrode aging and even causing voltage drops, thus reducing power generation efficiency and lifespan. Under light load, the output power is far below the rated value, slowing down the internal reaction rate and causing fuel waste. It may also lead to carbon buildup on the electrode catalyst layer, affecting long-term stability. Frequent start-stop cycles cause drastic fluctuations in internal humidity, temperature, and reaction interface conditions. Repeated "activation-dormancy" cycles exacerbate electrode material peeling, shortening fuel cell lifespan and potentially causing voltage surges at startup. When load demand changes rapidly, the fuel cell struggles to match its power output instantly, leading to excessive voltage fluctuations, potentially triggering overcurrent or overvoltage protection, affecting power supply continuity, and in extreme cases, causing temporary fuel cell failure.

[0006] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0007] This invention provides a distributed power management strategy for a hybrid electric propulsion system of an electric aircraft. It aims to solve the technical problems of existing power management strategies in hybrid electric propulsion systems of electric aircraft, which either focus only on dynamic power allocation and ignore steady-state control, or rely on the central controller / communication network and have reliability shortcomings. These strategies result in fuel cells being prone to efficiency reduction and lifespan degradation under adverse operating conditions such as heavy load, light load, and load fluctuations. Furthermore, the unreasonable division of functions of the energy storage unit can easily lead to overcharging and over-discharging, resulting in poor overall energy conversion efficiency and operational reliability of the system.

[0008] Other features and advantages of the invention will become apparent from the following detailed description, or may be learned in part by practice of the invention.

[0009] According to a first aspect of the present invention, a distributed power management strategy is provided in a hybrid electric propulsion system for an electric aircraft. The hybrid electric propulsion system includes a fuel cell unit, an energy storage battery unit, and a supercapacitor unit. Each unit is connected in parallel via a power converter to form a DC bus, and each unit is equipped with an independent local controller. The strategy operates based on local information of each unit, without a dedicated communication network, and balances steady-state and transient power allocation. Specifically, it includes: The local controller of the energy storage battery unit introduces a droop loop, using virtual resistance as the droop coefficient, to adjust the steady-state power of the fuel cell unit by discharging or charging, so that the fuel cell unit operates in the high-efficiency range, and the upper and lower limits of the battery output power current are determined by the battery's maximum discharge power, maximum charging power and battery state of charge. The local controller of the supercapacitor unit introduces a droop loop, which uses pure capacitance as the droop gain to bear the transient power of the system and suppress the impact of load fluctuations on the fuel cell unit. At the same time, it restores the state of charge of the supercapacitor through the output voltage offset. The dynamic response speed of the state of charge recovery control loop is much slower than that of the droop loop. The local controller of the fuel cell unit introduces a droop loop with virtual resistance as the droop gain. The external loop generates an offset. The fuel cell unit adaptively switches between voltage regulation mode and power regulation mode according to the propulsion load power and battery state of charge. In voltage regulation mode, the external voltage regulation loop is activated to restore the bus voltage. In power regulation mode, the output power is adjusted to the heavy load critical power or light load critical power. Ignoring feeder impedance, and based on the premise that the output voltage of each unit is equal to the bus voltage, the steady-state output power and steady-state load power of the battery are estimated. The operating mode of the fuel cell unit is determined according to the matching relationship between the estimated and actual steady-state load power. The system operating state is divided by combining the load power and the battery state of charge, so as to realize the adaptive switching of the fuel cell unit mode.

[0010] In some exemplary embodiments, the output voltage reference value of the energy storage battery cell is expressed as:

[0011] in, Rated DC voltage For virtual resistance, This represents the battery current.

[0012] In some exemplary embodiments, the state of charge recovery of the supercapacitor unit is achieved by adjusting the supercapacitor terminal voltage through a regulator and an integral coefficient, so that the supercapacitor's state of charge is maintained at a preset value, ensuring that it has the ability to handle dynamic power under any operating conditions.

[0013] In some exemplary embodiments, the output voltage reference value of the fuel cell is expressed as:

[0014] in, For fuel cell output current, It is the offset of the fuel cell output voltage. This is a reference value for the offset of the fuel cell output voltage.

[0015] In some exemplary embodiments, the steady-state load power estimate is the sum of the fuel cell output power and the battery steady-state output power estimate, which is calculated based on the battery droop curve and bus voltage.

[0016] In some exemplary embodiments, the system operating states include five types, which are divided according to whether the load power is in the high-efficiency range of the fuel cell and whether the battery state of charge is in the normal range. Under different operating states, the fuel cell unit matches the corresponding operating mode, and the energy storage battery unit and the supercapacitor unit realize power regulation according to their functional division of labor.

[0017] In some exemplary embodiments, when the load power is in the high-efficiency range of the fuel cell, the fuel cell unit operates in voltage regulation mode, undertakes all steady-state load power, and the bus voltage is restored to the rated value; When the load power exceeds the high efficiency range and the battery state of charge is normal, the fuel cell unit operates in power regulation mode, and the energy storage battery unit undertakes the steady-state power gap or absorbs the excess steady-state power. When the load power exceeds the high-efficiency range and the battery state of charge reaches its extreme value, the fuel cell unit first maintains the power regulation mode. After detecting the bus voltage or estimating the load power abnormality, it switches to the voltage regulation mode. The supercapacitor unit temporarily undertakes the steady-state power and then resumes to only handle transient power.

[0018] In some exemplary embodiments, in the power regulation mode of the fuel cell unit, the output power reference value is taken as the critical power under heavy load conditions and the critical power under light load conditions, so as to avoid the fuel cell unit operating in the heavy load or light load inefficient range.

[0019] In some exemplary embodiments, the extreme values ​​of the state of charge of the energy storage battery cell include a minimum value and a maximum value, which correspond to the over-discharge and over-charge states of the battery, respectively. When the extreme value is reached, the battery stops discharging or charging.

[0020] According to a second aspect of the present invention, a hybrid electric propulsion system for an electric aircraft is provided, employing the aforementioned distributed power management strategy. The system includes a fuel cell unit, an energy storage battery unit, a supercapacitor unit, a power converter, and a DC bus. Each unit is equipped with a local controller that operates based on local information, without a dedicated communication network. The fuel cell unit, the energy storage battery unit, and the supercapacitor unit are connected in parallel to the DC bus via the power converter.

[0021] The distributed power management strategy in the hybrid electric propulsion system of an electric aircraft provided by the embodiments of the present invention achieves multiple beneficial effects in terms of system efficiency, equipment lifespan, operational reliability, and energy consumption control, as detailed below: 1. Balancing steady-state and transient power distribution significantly improves system energy conversion efficiency. Clearly define the functional division of the battery and supercapacitor: the battery adjusts the fuel cell's steady-state operating point through a virtual resistance droop mechanism, ensuring it always operates within its high-efficiency range; the supercapacitor absorbs transient power based on a virtual capacitance droop mechanism, effectively suppressing load fluctuations. The two work together to achieve refined control of both steady-state and transient power, overcoming the shortcomings of traditional distributed strategies that only focus on dynamic power, and significantly improving the overall energy conversion efficiency of the hybrid electric propulsion system.

[0022] 2. Avoid adverse operating conditions of fuel cells, reduce hydrogen consumption and extend their service life. By adaptively switching between voltage and power modes of the fuel cell, and through the coordinated regulation of the battery and supercapacitor, the negative impact of heavy load, light load and rapid load fluctuations on the fuel cell can be effectively suppressed, avoiding problems such as membrane electrode aging, catalyst layer carbon deposition and electrode material peeling, and reducing hydrogen fuel waste. At the same time, it can prevent voltage drops, overcurrent / overvoltage protection and other situations caused by load fluctuations, extend the service life of the fuel cell, significantly reduce hydrogen fuel consumption and achieve economical system operation.

[0023] 3. Adopting a distributed control architecture improves the reliability and flexibility of system operation. The control algorithms of each unit (fuel cell, battery, supercapacitor) are all implemented based on local information, without the need for a dedicated communication network. This completely eliminates the dependence on the central controller and communication links, avoids the single point of failure risk of centralized strategies, and avoids the communication delay and data failure problems of traditional distributed strategies, thus greatly improving the operational reliability and operating condition adaptability of the power system.

[0024] 4. Precisely manage the operation of the energy storage unit, avoid safety risks and ensure its efficiency. Set upper and lower limit currents for battery output power determined by the state of charge and maximum charge / discharge power to effectively avoid safety issues such as overcharging and over-discharging of the battery. Adjust the state of charge of the supercapacitor by adjusting the voltage offset and maintain it at a preset value to ensure that it has the ability to handle dynamic power under any operating conditions. At the same time, design the response speed of the state of charge recovery control loop to be much slower than the droop loop to avoid interference with power management and give full play to the performance advantages of the energy storage unit.

[0025] 5. Achieve intelligent adaptive switching of operating modes to ensure stable power supply to the system. Based on the equivalent characteristics of the bus voltage, estimate the steady-state power of the battery and the steady-state load power. By matching the estimated values ​​with the actual values, and combining the load power and the battery state of charge, the system can automatically determine and switch the operating mode of the fuel cell. At the same time, it divides the system into five refined operating states to ensure that the system can operate stably under different load conditions and different battery state of charge. In voltage mode, the bus voltage can be restored to the rated value, and in power mode, the bus voltage deviation is within the allowable range, effectively ensuring the stability of the DC bus voltage and realizing continuous and reliable power supply to the hybrid electric propulsion system.

[0026] 6. Adaptable to the actual operating requirements of electric aircraft and possesses engineering application value: This strategy is designed for the actual operating conditions of electric aircraft with step changes in propulsion power. It has been verified by hardware-in-the-loop testing and can operate stably in medium, high, and low load ranges. Transient power is efficiently handled by supercapacitors, and steady-state power is reasonably distributed by fuel cells and batteries. All operating parameters (power, voltage, and state of charge) are within a controllable range. It is suitable for the aviation electrification application scenarios of electric aircraft and has good engineering feasibility and practical application value.

[0027] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Attached Figure Description

[0028] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0029] Figure 1 The structure of the hybrid electric propulsion system studied in this invention after adopting the proposed strategy; Figure 2 The graph shows the test results within a medium load range; Figure 3 The test results are shown in the following figures under high load range: (a) Battery SoC is normal, (b) Battery enters over-discharge process, (c) Battery continues to be over-discharged. Figure 4 The test results are shown in the following figures for low load range: (a) Battery SoC is normal, (b) Battery enters the overcharge process, (c) Battery is in a continuous overcharge state. Detailed Implementation

[0030] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided so that the invention will be more comprehensive and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0031] Furthermore, the accompanying drawings are merely illustrative of the invention and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0032] In hybrid electric propulsion system control, reducing hydrogen consumption and extending fuel cell lifespan are two common objectives. During actual operation, fuel cell efficiency drops sharply under heavy or light load conditions, leading to increased hydrogen consumption. Simultaneously, the additional lifespan degradation of fuel cells is mainly caused by four adverse operating conditions: start-stop transitions, heavy load, light load, and load fluctuations. To achieve these two objectives, both dynamic and steady-state power allocation must be considered simultaneously. However, existing distributed solutions only consider the dynamic power allocation problem, resulting in limited improvement in system performance.

[0033] To further improve the performance of hybrid electric propulsion systems, both dynamic and steady-state power distribution must be considered, which requires energy storage units. This invention employs a hybrid propulsion system composed of fuel cells, batteries, and supercapacitors, and proposes a distributed power management strategy. In this strategy, the fuel cell adaptively switches between voltage regulation and power regulation modes based on propulsion power demand and battery state of charge. Simultaneously, the batteries and supercapacitors respectively regulate the steady-state operating point of the fuel cell and absorb transient power. This strategy effectively suppresses the impact of load fluctuations and heavy / light load conditions on fuel cell performance without relying on communication resources, ensuring the economical and reliable operation of the hybrid electric propulsion system. It effectively suppresses the negative impacts of heavy / light load operation, load fluctuations, and frequent start-stop cycles on fuel cell operating efficiency and reliability, thereby reducing hydrogen consumption and extending service life.

[0034] The structure of the hybrid electric propulsion system after adopting the proposed strategy is shown in Figure 1. In this system, the fuel cell, energy storage battery, and supercapacitor are connected in parallel through a power converter to form a DC bus, providing the required power for the distributed propulsion system. In the control strategy proposed in this invention, all three units act as voltage sources and are equipped with local controllers, which are described below: In the first part, regarding the energy storage battery unit, given the high energy density of the battery, the steady-state operating point is adjusted in this invention. This is achieved when the propulsion power of the electric aircraft exceeds the heavy-load operation critical value of the fuel cell output power. Or below the critical value for light-load operation During operation, the battery regulates the steady-state power of the fuel cell by discharging or charging, ensuring it operates within its high-efficiency range. To achieve this, a droop loop is introduced into the battery cell's local controller, and a virtual resistance is incorporated. As the droop factor, the battery output voltage can be expressed as: ,in, Rated DC voltage This represents the battery current.

[0035] In addition, the battery output power is limited by the upper limit current. and lower limit current These two current values ​​are limited by the battery's maximum discharge power. Maximum charging power and battery state of charge ( ) Determined, the specific expression is as follows:

[0036]

[0037] in, and These are the minimum and maximum values ​​of the battery's state of charge, respectively. This is the battery input voltage.

[0038] In the second part, the supercapacitor is used to handle dynamic power and suppress the impact of load fluctuations in the system on the fuel cell. Similarly, a droop loop is introduced into the local controller of the supercapacitor, and the pure capacitor... As a droop gain, the reference value for the supercapacitor's output voltage can be expressed as:

[0039] in, s is the output current of the supercapacitor, and s is the Laplace operator in the circuit.

[0040] It should be noted that the formula includes the supercapacitor output voltage offset. Its function is to restore the state of charge of the supercapacitor. The state of charge of the supercapacitor can be restored by adjusting the terminal voltage of the supercapacitor. The recovery of ) is specifically expressed as:

[0041] in, and These are the terminal voltages of the supercapacitor and their reference values; For regulator, This is the integral coefficient. Through the above adjustment process, it can be... Maintaining the preset value ensures that the supercapacitor can handle dynamic power under any operating conditions. Meanwhile, to avoid the adjustment process affecting power management, the dynamic response speed of the control loop in the recovery expression is much slower than that of the droop loop.

[0042] In the third part, a droop loop is also introduced into the local controller of the fuel cell unit, and a virtual resistor is used. In addition to the droop gain, the outer loop will also generate an offset. Therefore, the reference value for the fuel cell output voltage can be expressed as:

[0043] in, For fuel cell output current, It is the offset of the fuel cell output voltage. This is a reference value for the offset of the fuel cell output voltage.

[0044] In the strategy proposed in this invention, the fuel cell can operate in two selectable modes: voltage mode and power mode.

[0045] When the fuel cell operates in voltage mode, an external voltage regulation loop is activated to restore voltage. At this time, The expression is:

[0046]

[0047] in, For external voltage regulator, is the integral coefficient.

[0048] When the fuel cell operates in power mode, its output power Adjusted to the critical value for heavy-load operation Or light load operating threshold This is to avoid the fuel cell operating under heavy or light load conditions. The expression is:

[0049] in, For external power regulator, The integral coefficient; The reference value for fuel cell output power is determined according to the following rules:

[0050] In determining the fuel cell operating mode, ignoring the influence of feeder impedance, the output voltage of all three units is equal to the bus voltage, i.e.:

[0051] The steady-state output power of the energy storage battery can be estimated as follows:

[0052] in, It is the virtual droop resistance of the battery module.

[0053] Since the supercapacitor only handles dynamic power, the steady-state load power can be estimated as follows:

[0054] in, This represents the steady-state output power of the fuel cell.

[0055] When the battery state of charge is within the normal range, the estimated load power under steady state is... Should be consistent with actual load power Equal. Conversely, when the battery's state of charge reaches its upper or lower limit, the battery's output power is limited, but the fuel cell cannot immediately detect this change, leading to... and Mismatch. Therefore, it can be achieved through... The changes are used to determine the operating mode of the fuel cell.

[0056] According to load power and battery state of charge The hybrid electric propulsion system studied has the following operating states: (1) When the load power meets The fuel cell operates in voltage mode, providing all steady-state load power. That is, regardless of the battery's state of charge... However, the actual steady-state power and estimated steady-state power of the battery are both zero. The external voltage regulation loop in the fuel cell controller allows the bus voltage to be restored to the rated voltage. .

[0057] (2) When the load power meets And the state of charge satisfies If the fuel cell were to bear the entire load demand, it would operate under heavy load conditions, leading to a decrease in operating efficiency. To avoid this, the fuel cell operates in power mode, and the power reference value... ,because The battery can compensate for the power shortfall and regulate the bus voltage by discharging. Therefore, the virtual resistance... This will cause a drop in bus voltage.

[0058] (3) When the load power meets And the state of charge satisfies In this case, the battery's maximum current... With the discharge rate capped at zero, the battery can no longer discharge. Lacking a communication mechanism, the fuel cell cannot immediately detect this change and continues operating in power mode. Therefore, the supercapacitor is forced to provide steady-state power to meet load demands, resulting in a continuous positive output current. It will cause the bus voltage The power output continues to decrease, which in turn leads to an increase in the estimated battery power. Increase along the battery droop curve, while simultaneously estimating the load power. And so it increases. During this process, Actual battery power Mismatch. As a result, the estimated load power... It will exceed the maximum load power. This situation is in It will not happen.

[0059] After this, the fuel cell will switch to voltage mode and operate under heavy load conditions, and the bus voltage will return to the rated voltage. Furthermore, the steady-state power of the supercapacitor will drop to zero, and state-of-charge recovery regulation will reduce the input voltage of the supercapacitor. Adjust to reference value .

[0060] (4) When the load power meets And the battery state of charge meets At this time, the fuel cell operates in power mode to avoid light load operation, with a power reference value. (Furthermore, the excess power generated by the fuel cell will increase the DC bus voltage. Based on the droop mechanism, the battery will be charged, and the charging power will meet the requirements.) This will cause a positive deviation in the bus voltage, while the battery state of charge will steadily increase.

[0061] (5) When the load power meets And the battery state of charge meets When the battery state of charge reaches its upper limit At that time, by lower limit current Setting it to zero will terminate the battery charging process. Initially, the fuel cell does not detect this change and continues to operate in power mode, forcing the supercapacitor to absorb excess steady-state power. Therefore, the bus voltage... It will continue to rise. Ultimately, the bus voltage... It will exceed the maximum value. Estimate load power It will become a negative value, which is something that usually doesn't happen. Therefore, it can be... > or <0 is used as an indicator for detecting battery overcharging.

[0062] Upon detecting an overcharge event, the fuel cell switches to voltage mode and operates under light load conditions, with the bus voltage returning to its rated value. Simultaneously, the supercapacitor's steady-state power gradually decreases to zero, and the input voltage... Restore to reference value When the fuel cell operates in voltage mode, the steady-state bus voltage is... Tracking rated voltage There is no voltage deviation; when the fuel cell operates in power mode, the bus voltage is regulated by the battery. Due to the droop mechanism and the battery's steady-state power, the bus voltage may deviate from the rated voltage. .

[0063] In this strategy, the supercapacitor handles dynamic propulsion power based on a virtual capacitor droop mechanism. Under heavy and light load conditions, the battery undertakes part of the steady-state load power through a virtual resistance droop mechanism, adjusting the steady-state operating point of the fuel cell and preventing it from operating in the inefficient range. Simultaneously, the fuel cell also employs virtual resistance and operates in two selectable modes based on the load power and battery state of charge. This strategy effectively suppresses severe load fluctuations and heavy / light load operation issues in the fuel cell, reducing hydrogen consumption and extending fuel cell lifespan. Notably, the control algorithms for all three units are implemented based on local information, eliminating the need for a dedicated communication network. By employing the proposed power allocation method, the fuel cell can avoid load fluctuations and heavy / light load conditions, ensuring the efficient and reliable operation of the hybrid power system.

[0064] To verify the feasibility of the proposed strategy, hardware-in-the-loop tests were conducted on the hybrid electric propulsion system shown in Figure 1, and the test results under different scenarios are presented.

[0065] When the load power meets During this test, the propulsion power changed in steps between 70 kW and 120 kW every 6 seconds, as shown in Figure 2. Under this condition, the fuel cell operated in voltage mode, handling all steady-state load power. Furthermore, during transient processes of load increase and decrease, the supercapacitor handled the mid-frequency and high-frequency dynamic load power; the battery did not provide steady-state power, only handling a small amount of mid-frequency power, and its state of charge remained stable. It can also be seen that under steady-state conditions, the bus voltage remained at its rated value.

[0066] When the load power meets In this case, the operating state of the hybrid electric propulsion system is affected by the battery state of charge. Influence.

[0067] When the battery state of charge meets At that time, the propulsion power changed in a step between 180 kW and 220 kW every 6 seconds, and the test results were as follows. Figure 3 As shown in (a), the fuel cell operates in power mode and, as an unschedulable unit, its power reference value is set to... Therefore, the output power is maintained stably at This ensures efficient operation of the fuel cell. Simultaneously, the battery fills the steady-state power gap through discharge, with output power varying between 40 kW and 80 kW, and the battery's state of charge steadily decreasing. Furthermore, during each transient process, the dynamic load power is handled by the supercapacitor, effectively suppressing voltage fluctuations and battery power variations. It is worth noting that the bus voltage is regulated by the battery through a virtual resistance droop mechanism, resulting in a decrease in bus voltage. When the load demand is 220 kW, the bus voltage drops to a minimum of 1960 V, and throughout the entire test, the bus voltage remains within the allowable range.

[0068] When the battery state of charge meets As the battery continues to discharge, its state of charge will decrease to [a certain value]. Subsequently, to avoid battery life degradation, the battery will cease discharging and will no longer have power output capability. Meanwhile, the fuel cell continues to operate in power mode, forcing the supercapacitor to provide positive steady-state power, causing the bus voltage to continuously drop, and the estimated load power in the fuel cell controller to decrease. The load power is continuously increasing. When the bus voltage drops below 1950 V, estimate the load power. It will exceed the maximum load power. Accordingly, the fuel cell detected an over-discharge event and switched to voltage mode. Subsequently, the fuel cell assumed full steady-state load power, operating under heavy load conditions, the supercapacitor's steady-state power dropped to zero, and the bus voltage returned to its rated value. The test results for this process are as follows: Figure 3 As shown in (b). When the hybrid electric propulsion system continues to operate under this condition, as... Figure 3 As shown in (c), the battery no longer bears the steady-state power, and the fuel cell always operates under heavy load conditions, with its output power varying with load demand. Meanwhile, during the transient process of load change, the dynamic power is still effectively handled by the supercapacitor.

[0069] When the load power meets Depending on the state of charge of the battery, the operating state of the hybrid electric propulsion system also varies.

[0070] When the battery state of charge meets In this scenario, the load power demand was set to periodically change between 10 kW and 40 kW every 6 seconds. The test results are as follows: Figure 4As shown in (a), the fuel cell operates in power mode, with a stable output power of 50 kW, ensuring efficient operation. Excess power generated by the fuel cell is absorbed by the battery, gradually increasing the battery's state of charge. Simultaneously, the supercapacitor handles dynamic power, effectively suppressing bus voltage fluctuations. Due to the negative steady-state power of the battery, a positive deviation occurs in the bus voltage, and this deviation varies with load demand, but remains below the maximum bus voltage. .

[0071] When the battery state of charge meets As the battery continues to charge, its state of charge will reach... At this point, the battery can no longer absorb excess power. However, the fuel cell has not yet detected this change and continues to operate in power mode, causing excess power to flow to the supercapacitor. Due to the use of a virtual capacitor as droop gain, the negative steady-state power of the supercapacitor causes the bus voltage to continuously rise, and the estimated load power to continuously decrease. When the bus voltage exceeds 2025 V, the estimated load power... When the value becomes negative, the fuel cell switches to voltage mode, the bus voltage returns to its rated value, only meeting the load power demand, and the steady-state power of the supercapacitor gradually decreases to zero, meaning the fuel cell is operating under light load conditions. The test results for this transition process are as follows: Figure 4 As shown in (b). When the battery is continuously in an overcharged state, as Figure 4 As shown in (c), the battery no longer provides steady-state power to regulate the operating point of the fuel cell, thereby preventing a further increase in the state of charge. Therefore, as Figure 4 As shown in (c), the fuel cell operates under light load conditions, with the bus voltage regulated to its rated value. In this scenario, the steady-state power of the fuel cell is determined by the load demand, while the dynamic power is still effectively handled by the supercapacitor.

[0072] Furthermore, the above figures are merely illustrative of the processes included in the method according to exemplary embodiments of the present invention, and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0073] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the claims.

[0074] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is defined only by the appended claims.

Claims

1. A distributed power management strategy for a hybrid electric propulsion system of an electric aircraft, characterized in that, The hybrid electric propulsion system includes a fuel cell unit, an energy storage battery unit, and a supercapacitor unit. Each unit is connected in parallel via a power converter to form a DC bus, and each unit is equipped with an independent local controller. The strategy operates based on local information of each unit, without a dedicated communication network, and takes into account both steady-state and transient power distribution. Specifically, it includes: The local controller of the energy storage battery unit introduces a droop loop, using virtual resistance as the droop coefficient, to adjust the steady-state power of the fuel cell unit by discharging or charging, so that the fuel cell unit operates in the high-efficiency range, and the upper and lower limits of the battery output power current are determined by the battery's maximum discharge power, maximum charging power and battery state of charge. The local controller of the supercapacitor unit introduces a droop loop, which uses pure capacitance as the droop gain to bear the transient power of the system and suppress the impact of load fluctuations on the fuel cell unit. At the same time, it restores the state of charge of the supercapacitor through the output voltage offset. The dynamic response speed of the state of charge recovery control loop is much slower than that of the droop loop. The local controller of the fuel cell unit introduces a droop loop with virtual resistance as the droop gain. The external loop generates an offset. The fuel cell unit adaptively switches between voltage regulation mode and power regulation mode according to the propulsion load power and battery state of charge. In voltage regulation mode, the external voltage regulation loop is activated to restore the bus voltage. In power regulation mode, the output power is adjusted to the heavy load critical power or light load critical power. Ignoring feeder impedance, and based on the premise that the output voltage of each unit is equal to the bus voltage, the steady-state output power and steady-state load power of the battery are estimated. The operating mode of the fuel cell unit is determined according to the matching relationship between the estimated and actual steady-state load power. The system operating state is divided by combining the load power and the battery state of charge, so as to realize the adaptive switching of the fuel cell unit mode.

2. The distributed power management strategy for the hybrid electric propulsion system of an electric aircraft according to claim 1, characterized in that, The reference value for the output voltage of the energy storage battery unit is expressed as follows: in, The rated DC voltage, For virtual resistance, This represents the battery current.

3. The distributed power management strategy for the hybrid electric propulsion system of an electric aircraft according to claim 1, characterized in that, The state of charge recovery of the supercapacitor unit is achieved by adjusting the terminal voltage of the supercapacitor through a regulator and an integral coefficient, so that the state of charge of the supercapacitor is maintained at a preset value, ensuring that it has the ability to handle dynamic power under any operating conditions.

4. The distributed power management strategy for the hybrid electric propulsion system of an electric aircraft according to claim 1, characterized in that, The reference value for the output voltage of the fuel cell is expressed as follows: in, For fuel cell output current, It is the offset of the fuel cell output voltage. This is a reference value for the offset of the fuel cell output voltage.

5. The distributed power management strategy for the hybrid electric propulsion system of an electric aircraft according to claim 1, characterized in that, The steady-state load power estimate is the sum of the fuel cell output power and the battery steady-state output power estimate, which is calculated based on the battery droop curve and bus voltage.

6. The distributed power management strategy for the hybrid electric propulsion system of an electric aircraft according to claim 1, characterized in that, The system operates in five states, which are determined by whether the load power is within the high-efficiency range of the fuel cell and whether the battery charge state is within the normal range. Under different operating states, the fuel cell unit matches the corresponding operating mode, and the energy storage battery unit and the supercapacitor unit perform power regulation according to their respective functions.

7. The distributed power management strategy for the hybrid electric propulsion system of an electric aircraft according to claim 6, characterized in that, When the load power is in the high-efficiency range of the fuel cell, the fuel cell unit operates in voltage regulation mode, bearing all steady-state load power, and the bus voltage is restored to the rated value. When the load power exceeds the high efficiency range and the battery state of charge is normal, the fuel cell unit operates in power regulation mode, and the energy storage battery unit undertakes the steady-state power gap or absorbs the excess steady-state power. When the load power exceeds the high-efficiency range and the battery state of charge reaches its extreme value, the fuel cell unit first maintains the power regulation mode. After detecting the bus voltage or estimating the load power abnormality, it switches to the voltage regulation mode. The supercapacitor unit temporarily undertakes the steady-state power and then resumes to only handle transient power.

8. The distributed power management strategy for the hybrid electric propulsion system of an electric aircraft according to claim 1, characterized in that, In the power regulation mode of the fuel cell unit, the output power reference value is taken as the critical power under heavy load conditions and the critical power under light load conditions, so as to avoid the fuel cell unit operating in the inefficient range of heavy load or light load.

9. The distributed power management strategy for the hybrid electric propulsion system of an electric aircraft according to claim 1, characterized in that, The extreme values ​​of the state of charge of the energy storage battery unit include the minimum and maximum values ​​of the state of charge, which correspond to the over-discharge and over-charge states of the battery, respectively. When the extreme value is reached, the battery stops discharging or charging.

10. A hybrid electric propulsion system for an electric aircraft, characterized in that, The system employs the distributed power management strategy described in any one of claims 1-9, comprising a fuel cell unit, an energy storage battery unit, a supercapacitor unit, a power converter, and a DC bus. Each unit is equipped with a local controller that operates based on local information, without a dedicated communication network. The fuel cell unit, the energy storage battery unit, and the supercapacitor unit are connected in parallel to the DC bus via the power converter.

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