Proton exchange membrane fuel cell waste heat recovery ejector refrigeration system and control method

Abstract

The application discloses a proton exchange membrane fuel cell waste heat recovery ejection type refrigeration system and a control method. The system comprises a fuel cell thermal management subsystem and an ejection type refrigeration subsystem coupled through a heat exchanger. The ejection type refrigeration subsystem is provided with a flow path selection unit and an auxiliary heating unit, forming a switchable dual-heat source driving structure. The control method first estimates the effective waste heat output of the fuel cell online, then compares it with the system refrigeration demand in real time, and intelligently switches the system among three working modes according to the comparison result. When the waste heat is sufficient, only the waste heat is used for driving; when the waste heat is insufficient, the auxiliary heating is started synchronously and the working medium flow is accurately distributed to supplement the heat; when the waste heat is interrupted, the auxiliary heating unit is independently powered, and a high-level algorithm is used to ensure smooth power supply. The application solves the problems that the low-temperature waste heat of the fuel cell is difficult to recover and utilize, the traditional cooling energy consumption is high, and thermal pollution is caused.

Description

Technical Field

[0001] This invention relates to the field of hydrogen energy power technology, specifically to a waste heat recovery ejector refrigeration system and control method for proton exchange membrane fuel cells. Background Technology

[0002] Hydrogen energy, as a key secondary energy source, has seen its efficient and clean utilization technologies become a core direction for global energy transformation. Proton exchange membrane fuel cells (PEMFCs), with their outstanding advantages such as low operating temperature, rapid start-up, high power density, and zero emissions, have shown enormous application potential in fields such as new energy vehicles, distributed power generation, drones, and portable power supplies.

[0003] However, while PEMFCs efficiently convert the chemical energy of hydrogen into electrical energy, they also present significant challenges in thermal management. The ideal operating temperature for PEMFCs is typically between 60°C and 80°C, with an energy conversion efficiency of approximately 40%–50%. This means that as much as 50%–60% of the input chemical energy is dissipated as heat, and this waste heat, due to its temperature below 80°C, is considered low-grade waste heat. Although this low-grade waste heat has a low temperature, its total amount is considerable, and if it cannot be effectively recovered and utilized, it will result in a huge waste of energy.

[0004] Currently, the mainstream thermal management solution for PEMFC systems is an active liquid cooling cycle. The coolant (such as an aqueous ethylene glycol solution) flows through the internal channels of the fuel cell stack, absorbing the heat generated by the electrochemical reaction, and then directly dissipates the heat into the atmosphere via air-cooled or secondary liquid-cooled radiators. This traditional solution has three significant drawbacks: First, low energy utilization. Directly discarding low-grade waste heat fails to achieve cascaded energy utilization, making it difficult for the overall system energy efficiency to break through the theoretical bottleneck of 50%. Second, "parasitic power" losses exist. Driving auxiliary equipment such as cooling circulation pumps and cooling fans requires continuous consumption of the valuable electrical energy generated by the PEMFC itself. This "parasitic load" typically accounts for 5% to 10% of the system's net output power, further reducing the system's effective output and operational economy. Third, it causes environmental thermal pollution. Centralized waste heat emissions can lead to increased local ambient temperatures around the equipment, especially in high-power-density or enclosed space applications, which contradicts the green and environmentally friendly concept of hydrogen energy technology.

[0005] On the other hand, to maintain a suitable temperature in PEMFC system auxiliary equipment or vehicle passenger compartment, a separate vapor compression refrigeration system is usually required. These systems rely on electrically driven mechanical compressors, whose core components suffer from wear and tear, noise and vibration, and potential refrigerant leakage. Furthermore, their operating energy consumption directly increases the overall energy consumption burden of the vehicle or system. With increasingly stringent requirements for energy conservation and emission reduction across society, developing a low-carbon refrigeration technology that can replace or assist traditional electrically driven refrigeration and achieve internal energy recycling has become an urgent technological need in the field of PEMFC system integration.

[0006] While some existing technologies have attempted to utilize the waste heat from high-temperature solid oxide fuel cells (SOFCs) for cooling or power generation, the significantly low temperature of PEMFC waste heat makes directly applying medium-to-high-temperature waste heat recovery technologies (such as the Rankine cycle) extremely inefficient and economically unfeasible. Therefore, exploring an efficient, reliable, and deeply integrated waste heat recovery and cooling technology that can be deeply coupled with the thermal management system, specifically addressing the low-temperature and fluctuating waste heat characteristic of PEMFCs, is of crucial practical significance for improving the overall energy efficiency of PEMFC systems, reducing auxiliary power consumption, and achieving truly green energy operation. Currently, there is a lack of mature, efficient, and engineering-feasible systematic solutions in this field. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention provides a proton exchange membrane fuel cell waste heat recovery ejector refrigeration system and its control method. This system recovers low-grade waste heat (60-80℃) generated by the fuel cell and transfers it to an ejector refrigeration subsystem. The high-temperature, high-pressure refrigerant after heat exchange drives the ejector, thereby generating a cooling effect. This system can convert the waste heat from traditional cooling methods into effective cooling capacity, while avoiding the additional 5%-10% energy consumption of traditional cooling systems and solving the thermal pollution problem caused by direct waste heat discharge. This invention also provides a corresponding multi-mode intelligent control method, which dynamically adjusts heat source compensation and fluid path to ensure efficient and stable operation of the system under different operating conditions. This technical solution uses waste heat to replace electrical energy for refrigeration, significantly improving the system's energy utilization efficiency and meeting the requirements of green and low-carbon development.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] The proton exchange membrane fuel cell waste heat recovery ejector refrigeration system includes:

[0010] The fuel cell thermal management subsystem has an internal coolant circulation system to absorb and transfer the waste heat generated by the proton exchange membrane fuel cell stack.

[0011] The ejector refrigeration subsystem has a refrigerant circulating internally as the working fluid. The ejector refrigeration subsystem is thermally coupled to the fuel cell thermal management subsystem through a heat exchanger, which is used to receive the transferred waste heat to drive the refrigerant and generate a cooling effect.

[0012] The ejector-type refrigeration subsystem also includes a flow path selection unit and an auxiliary heating unit. The flow path selection unit adjusts the flow path of the refrigerant, allowing the refrigerant to selectively receive waste heat from the fuel cell thermal management subsystem or supplementary heat from the auxiliary heating unit, thereby driving the refrigerant and maintaining a stable output of the refrigeration effect.

[0013] Furthermore, the fuel cell thermal management subsystem and the ejector refrigeration subsystem are thermally coupled through a heat exchanger.

[0014] Furthermore, the fuel cell thermal management subsystem includes a coolant circulation pump, a proton exchange membrane fuel cell stack, and a first flow channel of a heat exchanger, all connected via a first pipeline.

[0015] The ejector-type refrigeration subsystem includes a refrigerant circulation pump, a second flow channel of a heat exchanger, an ejector, and a condenser, all connected by a second pipeline. The flow path selection unit and the auxiliary heating unit are connected in series, and the series structure formed by the flow path selection unit and the auxiliary heating unit is arranged in parallel with the second flow channel of the heat exchanger between the refrigerant circulation pump and the ejector.

[0016] Furthermore, the flow path selection unit is a three-way valve; the inlet of the three-way valve is connected to the outlet of the refrigerant circulation pump, the first outlet is connected to the inlet of the second flow channel of the heat exchanger, and the second outlet is connected to the inlet of the auxiliary heating unit.

[0017] The outlet of the second flow channel of the heat exchanger and the outlet of the auxiliary heating unit are connected together through pipelines and then connected to the primary flow inlet of the ejector.

[0018] Furthermore, the ejector outlet is connected to the condenser inlet, and the condenser outlet is divided into two paths: one path is connected to the evaporator inlet through a throttling device; the other path is connected to the refrigerant circulation pump inlet; the evaporator outlet is connected to the secondary flow inlet of the ejector.

[0019] The auxiliary heating unit is an electric heater, and the throttling device is an expansion valve.

[0020] Furthermore, the ejector includes a nozzle, a suction chamber, a mixing chamber, and a diffusion chamber that are sequentially connected along the fluid flow direction;

[0021] The nozzle inlet forms the primary flow inlet of the ejector, and the side wall of the suction chamber is provided with the secondary flow inlet of the ejector.

[0022] A control method for a proton exchange membrane fuel cell waste heat recovery ejector refrigeration system includes the following steps:

[0023] S1. Based on the operating parameters and coolant parameters of the proton exchange membrane fuel cell stack, determine the waste heat output of the proton exchange membrane fuel cell stack; establish a state observation model integrating the thermal dynamics of the proton exchange membrane fuel cell stack and the time-varying heat transfer efficiency of the heat exchanger; by introducing a feedback correction term including the temperature of the proton exchange membrane fuel cell stack, the coolant flow rate, and the temperature difference across the heat exchanger, estimate and correct the current effective waste heat output transferred through the heat exchanger online. ;

[0024] S2. The current effective waste heat output... With reference driving heat set according to cooling demand Real-time comparison is performed, and based on the comparison results, the system adaptively switches between the following three operating modes. Corresponding coordinated control is executed by coordinating the fluid path allocation of the flow path selection unit with the power output of the auxiliary heating unit:

[0025] Rated operating mode: When At the same time, the flow path selection unit controls the refrigerant to flow completely through the second flow path of the heat exchanger, and uses a PI controller to adjust the refrigerant circulation flow rate to match the waste heat output, while shutting down the auxiliary heating unit.

[0026] Low power compensation mode: when At that time, calculate the heat deficit. , = - The following two controls are executed in parallel:

[0027] Control a: Based on heat deficit The deviation between the actual temperature and the target temperature of the refrigerant is used to dynamically adjust the output power of the auxiliary heating unit using a fuzzy PID algorithm.

[0028] Control b: with To achieve the target ratio, the flow distribution of refrigerant between the heat exchanger and the auxiliary heating unit is controlled by adjusting the opening degree of the flow path selection unit, and feedback correction is performed based on the monitoring of the distributed flow to make the actual distribution ratio approach the target ratio.

[0029] Fault backup mode: when When the refrigerant level is zero, approaches zero, or the proton exchange membrane fuel cell stack stops operating, the control flow path selection unit ensures that the refrigerant flows completely through the auxiliary heating unit, and a model predictive control algorithm is used to adjust the output power of the auxiliary heating unit. The prediction model of the model predictive control algorithm is a first-order inertial model of the auxiliary heating unit. During the optimization process of the model predictive control algorithm, the goal is to minimize the reference driving heat. Temperature and power fluctuations during the transmission process are the optimization objectives.

[0030] Furthermore, the state observation model is a Luneburger observer. The feedback correction term includes the residual consisting of the difference between the actual measured outlet temperature of the proton exchange membrane fuel cell stack and the temperature estimated by the observer. After weighting the residual through the designed observer gain matrix, it is fed back into the state observer model to dynamically correct the current effective waste heat output. The estimated value.

[0031] Furthermore, in control b of the low-power compensation mode, a composite control strategy combining feedforward and feedback control is adopted for the refrigerant flow distribution process; wherein:

[0032] Feedforward control generates a reference control command based on the target ratio.

[0033] Feedback control is based on real-time monitoring of the actual allocation ratio, calculating the deviation between the actual allocation ratio and the target ratio, and correcting the deviation through a PID controller to output a correction control command.

[0034] The baseline control command and the correction control command are superimposed to generate the final control command used to control the flow path selection unit.

[0035] Furthermore, the transfer function of the first-order inertial model for:

[0036] ;

[0037] in, For the Laplace operator, For model gain, It is a time constant;

[0038] Optimization objective function of model predictive control algorithm for:

[0039] :

[0040] in, To predict the time domain, To control the time domain, For the first The predicted temperature of the step, The set temperature for the refrigerant. For the first The change in power at each step and These are the weighting coefficients;

[0041] The constraints that the optimization process needs to meet include: the upper limit of the power of the auxiliary heating unit. and the upper limit of the rate of change of power .

[0042] Furthermore, the fuzzy PID algorithm will calculate the real-time temperature difference. Divide into at least five fuzzy sets and pre-set corresponding fuzzy rule bases. = - ,in The actual temperature of the refrigerant; the fuzzy rule base contains multiple inference rules used to dynamically adjust the proportional gain of the PID controller based on the fuzzy set to which the temperature difference belongs. and integral gain .

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1. This invention addresses the challenge of low-grade waste heat recovery in proton exchange membrane fuel cell stacks by innovatively constructing an ejector-type refrigeration cycle system driven by the stack's waste heat. This system can directly convert 30%-50% of the stack's output energy, representing low-temperature waste heat, into refrigeration power. It completely eliminates the passive heat dissipation mode of traditional cooling systems, which requires an additional 5%-10% of electrical power. This represents a fundamental shift from energy-consuming heat dissipation to waste heat-driven cooling, significantly improving the overall energy efficiency of the system and aligning with the requirements of green and low-carbon development.

[0045] 2. Compared to traditional electric refrigeration systems that rely on mechanical compressors, this invention employs a thermally driven ejector refrigeration cycle. Its core driving component, the ejector, has no moving parts, fundamentally eliminating the mechanical wear, vibration noise, and lubricant contamination problems associated with compressors. The system structure is simpler, more reliable, and operates without direct carbon emissions or noise pollution, exhibiting excellent environmental compatibility.

[0046] 3. Addressing the core challenge of large and discontinuous waste heat output fluctuations in proton exchange membrane fuel cell stacks, this invention proposes a dynamic thermal balance control strategy based on multimodal intelligent collaboration. The system estimates effective waste heat in real time through a state observer and, combined with forward-looking power fluctuation prediction, can seamlessly and adaptively switch between rated, low-power compensation, and fault standby modes. Through the synergy of algorithms such as fuzzy PID, model predictive control, and feedforward-feedback composite control, it achieves rapid and precise adjustment of auxiliary heating power and refrigerant flow rate. This enables the system to stably control refrigerant temperature fluctuations within ±1℃ even under conditions of drastic stack power fluctuations, fundamentally solving the efficiency reduction and output fluctuation problems caused by unstable heat sources in traditional systems, and significantly improving the system's reliability, energy efficiency, and environmental adaptability.

[0047] 4. In low-power compensation mode, this system innovatively adopts a collaborative mechanism of on-demand flow distribution and precise heat compensation, rather than a simple heat source switching. By ensuring that the refrigerant flows through the parallel main and auxiliary heat sources in the optimal ratio, throttling and mixing losses are minimized, ensuring that the system can maintain efficient and stable operation over a wide load range. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the structure of the present invention.

[0049] Figure 2 This is a schematic diagram of the ejector structure.

[0050] Figure 3 This is a diagram showing the switching between the three working modes of the present invention.

[0051] The names corresponding to the reference numerals in the attached figures are as follows:

[0052] 1-Coolant circulation pump, 2-Proton exchange membrane fuel cell stack, 3-Heat exchanger, 4-Refrigerant circulation pump, 5-Flow path selection unit, 6-Auxiliary heating unit, 7-Ejector, 8-Condenser, 9-Throttling device, 10-Evaporator. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0054] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0055] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; of course, they can also refer to a mechanical connection or an electrical connection; furthermore, they can refer to a direct connection, an indirect connection through an intermediate medium, or a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0056] Example 1. As... Figure 1 and Figure 2 As shown, the proton exchange membrane fuel cell waste heat recovery ejector refrigeration system includes a fuel cell thermal management subsystem and an ejector refrigeration subsystem. The fuel cell thermal management subsystem internally circulates a coolant (such as an aqueous ethylene glycol solution) to absorb and transfer the waste heat generated by the proton exchange membrane fuel cell stack.

[0057] The ejector refrigeration subsystem has a refrigerant (such as 2,3,3,3-tetrafluoropropylene) circulating internally as the working fluid. The ejector refrigeration subsystem is thermally coupled to the fuel cell thermal management subsystem through heat exchanger 3, which is used to receive the transferred waste heat to drive the refrigerant and generate a cooling effect.

[0058] As the sole energy exchange interface between two independent circulation loops (coolant loop and refrigerant loop), heat exchanger 3 efficiently and controllably transfers the waste heat (i.e., residual heat) generated by the proton exchange membrane fuel cell stack from the high-temperature coolant to the low-temperature refrigerant, thereby converting low-grade waste heat into effective thermal energy to drive the ejector refrigeration cycle. This not only achieves cross-medium heat transfer but also structurally ensures complete isolation between the reactant gases and the refrigerant, guaranteeing the safety and reliability of the system operation.

[0059] The fuel cell thermal management subsystem includes a coolant circulation pump 1, a proton exchange membrane fuel cell stack 2, and a first flow channel of a heat exchanger 3, all connected via a first pipeline. The proton exchange membrane fuel cell thermal management subsystem forms a closed-loop forced coolant circulation circuit. Driven by the coolant circulation pump 1, the coolant flows through the proton exchange membrane fuel cell stack 2 to absorb the waste heat generated by the reaction, becoming a heat-carrying medium. It then enters the first flow channel of the heat exchanger 3 to release heat, completing a full waste heat collection and transfer cycle.

[0060] The ejector-type refrigeration subsystem includes a refrigerant circulation pump 4, a second flow channel of a heat exchanger 3, an ejector 7, and a condenser 8, all connected via a second pipeline. The flow path selection unit 5 and the auxiliary heating unit 6 are connected in series, forming a series structure between the refrigerant circulation pump 4 and the ejector 7, and parallel to the second flow channel of the heat exchanger 3. The ejector-type refrigeration subsystem thus constitutes a refrigerant circulation loop with the ejector 7 as the core power component. Driven by the refrigerant circulation pump 4, the refrigerant forms a high-pressure liquid.

[0061] The ejector-type refrigeration subsystem also includes a flow path selection unit 5 and an auxiliary heating unit 6. The flow path selection unit 5 adjusts the refrigerant's flow path, allowing the refrigerant to selectively receive waste heat from the fuel cell thermal management subsystem or supplementary heat from the auxiliary heating unit 6 to drive the refrigerant and maintain a stable output of the refrigeration effect. In this invention, an auxiliary heat source branch, consisting of the flow path selection unit 5 and the auxiliary heating unit 6 connected in series, is installed on the pipeline from the refrigerant circulation pump 4 to the ejector 7. This branch is connected in parallel with the second flow channel of the heat exchanger 3. This parallel architecture is the physical basis for the system to achieve flexible switching and coordination of multiple heat sources. It allows the high-pressure refrigerant to select, according to control commands, flow through the main heat source (heat exchanger, absorbing waste heat) or the auxiliary heat source (electric heater, supplementing heat), or be diverted to both in a certain proportion, thereby providing the ejector 7 with a stable and adjustable high-temperature, high-pressure driving airflow, ultimately achieving the refrigeration effect through condensation, throttling, and evaporation processes.

[0062] The flow path selection unit 5 is a three-way valve. The inlet of the three-way valve connects to the outlet of the refrigerant circulation pump 4, the first outlet connects to the inlet of the second flow channel of the heat exchanger 3, and the second outlet connects to the inlet of the auxiliary heating unit 6. The outlet of the second flow channel of the heat exchanger 3 and the outlet of the auxiliary heating unit 6 merge through a pipeline and are connected to the primary flow inlet of the ejector 7. The inlet of the three-way valve serves as the total input, receiving all the high-pressure working fluid from the refrigerant circulation pump 4; its two outlets constitute two independent heat source paths: the first outlet connects to the main waste heat recovery path (i.e., the second flow channel of the heat exchanger 3), and the second outlet connects to the auxiliary heating path (i.e., the auxiliary heating unit 6). By driving the valve core to rotate to different opening degrees, the three-way valve can continuously adjust the refrigerant flow ratio to these two paths, achieving a smooth transition between any state from completely waste heat-driven to completely electric-heat-driven. Finally, the heated refrigerants flowing from the main and auxiliary heat sources mix at the confluence point to form a driving working fluid whose temperature and flow rate both meet the primary flow requirements of the ejector 7.

[0063] The outlet of ejector 7 is connected to the inlet of condenser 8. The outlet of condenser 8 is divided into two paths: one path connects to the inlet of evaporator 10 via throttling device 9; the other path connects to the inlet of refrigerant circulation pump 4. The outlet of evaporator 10 is connected to the secondary flow inlet of ejector 10. The pressurized mixed gas discharged from the outlet of ejector 7 enters condenser 8, where it condenses and releases heat, becoming high-pressure liquid refrigerant. The liquid working fluid is then split: the main branch is throttled and depressurized by throttling device 9, forming a low-temperature, low-pressure gas-liquid two-phase flow before entering evaporator 10 to absorb heat and vaporize (producing a refrigeration effect); the bypass branch returns directly to the inlet of refrigerant circulation pump 4, completing the high-pressure side circulation. The low-temperature, low-pressure refrigerant vapor generated at the outlet of evaporator 10 is drawn in by the low pressure formed inside ejector 7 during operation and enters through its secondary flow inlet, thus completing the closed-loop circulation of the entire working fluid. This invention replaces the pressurization and suction functions of a traditional compressor with an ejector, realizing a refrigeration cycle without mechanical moving parts.

[0064] The ejector 7 is internally composed of four functional sections: a nozzle 71, a suction chamber 72, a mixing chamber 73, and a diffusion chamber 74. The inlet of the nozzle 71 is its primary flow inlet, receiving high-temperature, high-pressure refrigerant gas. The side wall of the suction chamber 72 has a secondary flow inlet for drawing in low-temperature, low-pressure vapor from the evaporator 10. Its working principle is as follows: the high-pressure primary flow gas expands and accelerates into a supersonic jet within the nozzle 71, which is injected into the suction chamber 72, creating a strong negative pressure zone, thereby drawing in the secondary flow vapor. The two fluids undergo sufficient momentum and mass exchange and mix within the mixing chamber 73. The mixed fluid finally enters the diffusion chamber 74, where its velocity decreases, kinetic energy is converted into pressure energy, and it is then pressurized before being discharged. This invention's ejector 7, through its specific structure of sequentially connected nozzle, suction chamber, mixing chamber, and diffusion chamber, achieves the core pneumatic process of converting primary flow pressure energy into ejector kinetic energy to draw in the secondary flow, and converting the mixed kinetic energy back into pressure energy, thus simultaneously completing the two key functions of suction and pressurization within an integrated structure.

[0065] The auxiliary heating unit 6 is an electric heater that directly heats the refrigerant flowing through it via electrical energy input, ensuring the continuity and stability of the system's heat input. The throttling device 9 is an expansion valve that performs isenthalpic throttling expansion on the high-pressure liquid refrigerant from the condenser 8, causing it to rapidly decrease in pressure and temperature, transforming it into a low-temperature, low-pressure gas-liquid two-phase state. This creates the necessary initial conditions for the refrigerant to boil and absorb heat (i.e., the refrigeration effect) in the evaporator 10.

[0066] Example 2. (As shown) Figure 3 As shown, the control method for a proton exchange membrane fuel cell waste heat recovery ejector refrigeration system includes the following steps:

[0067] S1. Based on the operating parameters and coolant parameters of the proton exchange membrane fuel cell stack, determine the waste heat output of the proton exchange membrane fuel cell stack; establish a state observation model integrating the thermal dynamics of the proton exchange membrane fuel cell stack and the time-varying heat transfer efficiency of the heat exchanger; by introducing a feedback correction term including the temperature of the proton exchange membrane fuel cell stack, the coolant flow rate, and the temperature difference across the heat exchanger, estimate and correct the current effective waste heat output transferred through the heat exchanger online. ;

[0068] S2. The current effective waste heat output... With reference driving heat set according to cooling demand Real-time comparison is performed, and based on the comparison results, the system adaptively switches between the following three operating modes. Corresponding coordinated control is executed by coordinating the fluid path allocation of the flow path selection unit with the power output of the auxiliary heating unit:

[0069] Rated operating mode: When At the same time, the flow path selection unit controls the refrigerant to flow completely through the second flow path of the heat exchanger, and uses a PI controller to adjust the refrigerant circulation flow rate to match the waste heat output, while shutting down the auxiliary heating unit.

[0070] Low power compensation mode: when At that time, calculate the heat deficit. , = - The following two controls are executed in parallel:

[0071] Control a: Based on heat deficit The deviation between the actual temperature and the target temperature of the refrigerant is used to dynamically adjust the output power of the auxiliary heating unit using a fuzzy PID algorithm.

[0072] Control b: with To achieve the target ratio, the flow distribution of refrigerant between the heat exchanger and the auxiliary heating unit (6) is controlled by adjusting the opening degree of the flow path selection unit, and feedback correction is performed based on the monitoring of the flow after distribution, so that the actual distribution ratio approaches the target ratio.

[0073] Fault backup mode: when When the refrigerant level is zero, approaches zero, or the proton exchange membrane fuel cell stack stops operating, the control flow path selection unit ensures that the refrigerant flows completely through the auxiliary heating unit, and a model predictive control algorithm is used to adjust the output power of the auxiliary heating unit. The prediction model of the model predictive control algorithm is a first-order inertial model of the auxiliary heating unit. During the optimization process of the model predictive control algorithm, the goal is to minimize the reference driving heat. Temperature and power fluctuations during the transmission process are the optimization objectives.

[0074] This method first uses S1, employing a state observation model of integrated fuel cell stack thermal dynamics and time-varying efficiency of the heat exchanger, to estimate and correct the current effective waste heat output actually transferred by the heat exchanger in real time. This solves the problem of heat transfer uncertainty caused by heat exchanger performance degradation and changes in operating conditions.

[0075] Then in S2, the system will With the reference driving heat required to maintain cooling Real-time comparisons are performed, and the system is driven to autonomously make decisions and switch between three modes based on this comparison.

[0076] In rated operating mode, sufficient waste heat is fully utilized, and the flow rate is precisely adjusted through a PI controller (proportional-integral controller) to achieve thermal balance. The electric heater is turned off, achieving zero additional energy consumption operation.

[0077] In low-power compensation mode, when faced with insufficient waste heat, the system activates a dual-loop collaborative mechanism: control a uses a fuzzy PID algorithm to dynamically adjust the power of the electric heater to accurately compensate for the heat gap; control b adjusts the opening of the three-way valve to achieve the on-demand proportional distribution of refrigerant between the waste heat source and the electric heat source, ensuring the matching of heat and medium.

[0078] In failover mode, when waste heat is interrupted, the system seamlessly switches to being powered entirely by electric heaters. The model predictive control (MPC) algorithm is used to optimize the control process and minimize temperature and power fluctuations while meeting safety constraints such as power change rate, so as to achieve a smooth and efficient takeover of the backup heat source.

[0079] The entire control method achieves efficient recovery and utilization of fluctuating heat sources and high stability control of system output through a closed loop of precise sensing → intelligent decision-making → collaborative execution.

[0080] Before establishing a state observation model, it is necessary to first determine the theoretical waste heat output of the fuel cell stack based on measurable operating parameters, which serves as the initial input and benchmark for model calculation. Specifically, by collecting real-time operating parameters of the proton exchange membrane fuel cell stack (such as output current, voltage, and internal stack temperature) and cooling circuit parameters (such as the temperature and flow rate of the coolant flowing into the proton exchange membrane fuel cell stack), and based on the thermodynamic model and energy balance equation of the stack, the total waste heat power released by the stack in the form of heat under the current operating conditions, i.e., waste heat output, is calculated or estimated in real time using the electrochemical energy balance method or the coolant heat carrying method.

[0081] Among them, the waste heat output of the fuel cell stack is calculated in real time using the coolant heat carrying method. (i.e., theoretical waste heat output) The specific operation is as follows: The volumetric flow rate of the coolant flowing through the fuel cell stack is measured in real time using a flow sensor (such as a vortex flow meter) and a platinum resistance thermometer (PT100). Coolant inlet temperature With outlet temperature Ignoring a small amount of heat dissipation from the fuel cell stack casing, and assuming that all waste heat is absorbed by the coolant, the theoretical waste heat output is calculated using the following formula: - In the formula: and These are the average density and average specific heat capacity of the coolant used, respectively.

[0082] To achieve a high-precision estimate of the current effective waste heat output, this invention constructs and implements an integrated state observation model based on the Luneburger observer theory. The specific steps are as follows:

[0083] 1. State-space modeling.

[0084] First, the heat generation dynamics of the proton exchange membrane fuel cell stack and the heat transfer process of the heat exchanger (using time-varying coefficients) are analyzed. The efficiency of the characterization has decreased. Physical processes such as the decay constant are modeled as a set of discrete-time state equations, forming the mathematical model basis of the observer. The selected state variables... Including: average temperature of fuel cell stack Heat exchanger coolant side outlet temperature Heat exchanger refrigerant side outlet temperature and the Time-varying efficiency decay coefficient at each sampling time .

[0085] 2. Observer operation and feedback correction.

[0086] As a real-time running algorithm module, the Romberg observer performs the following operations in each control cycle:

[0087] Obtain the real-time measured fuel cell outlet temperature by the sensor. Coolant flow rate and the temperature difference between the two sides of the heat exchanger And input it into the observer.

[0088] Based on its built-in mathematical model (which consists of a set of state equations describing the thermal dynamics of the electric stack and the time-varying heat transfer process of the heat exchanger), the state estimate of the previous moment, and the current system input, the observer calculates the internal estimates of each state variable and the corresponding output at the current moment.

[0089] The measured values ​​are compared with the corresponding internal estimates to obtain the measurement residuals.

[0090] The residual is weighted using a pre-designed and optimized observer gain matrix to generate a state correction. This correction is then fed back into the state estimation equation, dynamically updating and correcting all state estimates within the observer. The core function of this closed-loop mechanism is to continuously adjust the time-varying efficiency decay coefficient. Online identification and real-time updates are performed to ensure that model parameters always track changes in actual physical processes.

[0091] 3. Output effective waste heat.

[0092] Based on more accurate state estimates after real-time correction by the observer (especially the updated ones) Temperature estimation can be achieved through heat transfer formulas (such as...) = , for The updated value, The heat transfer coefficient of the heat exchanger is . The heat transfer area of ​​the heat exchanger. The current effective waste heat output is calculated with high precision based on the logarithmic mean temperature difference between the coolant and refrigerant along the flow direction in the heat exchanger. .

[0093] Multi-mode adaptive switching and collaborative control based on heat comparison. This involves continuously comparing the current effective waste heat output. With reference driving heat set according to cooling demand This drives the system to seamlessly switch between three operating modes. (Base drive heat) The heat input required for the system to operate stably under design conditions is a preset or online-adjustable constant.

[0094] Rated operating mode: When At this point, it indicates that the waste heat from the fuel cell stack is sufficient to independently drive the system. The control valve spool is at its fully open position (100% opening), allowing the refrigerant to flow completely through the second flow path of the heat exchanger, while simultaneously shutting off the electric heater. Using... PI The controller, with the target evaporation temperature of the refrigerant or the outlet temperature of the heat exchanger as the set value, dynamically matches the refrigerant circulation flow rate and the changing waste heat output by adjusting the speed of the refrigerant circulation pump, thus maintaining thermal balance.

[0095] In rated operating mode, the system monitors the outlet temperature of the fuel cell stack and the evaporation pressure of the refrigerant in real time, and uses the feedback regulation of the PI controller to strictly control the temperature stability of the refrigerant within ±1℃.

[0096] Low power compensation mode: when This indicates insufficient waste heat and a heat deficit. Calculate the heat deficit. , = - The following two controls are executed in parallel:

[0097] Control a: The output power of the electric heater is dynamically adjusted using a fuzzy PID algorithm. The fuzzy PID algorithm uses the heat gap as a reference. and the deviation between the actual temperature of the refrigerant and the set temperature As the primary input, = - ,in This refers to the actual temperature of the refrigerant. The fuzzy PID algorithm will use the real-time temperature difference. It is divided into at least five fuzzy sets (negative large, negative small, zero, positive small, positive large), each fuzzy set corresponding to a different temperature deviation range. For example, negative large means that the actual temperature is significantly lower than the set value, while positive large means that the actual temperature is significantly higher than the set value.

[0098] The fuzzy rule base predefines five core inference rules, each corresponding to one of five fuzzy sets:

[0099] When the temperature difference is "negatively large": the system significantly increases the proportional gain. and integral gain This generates a strong control effect, rapidly reduces negative deviation, and enhances the system response speed.

[0100] When the temperature difference is "negatively small": the system will increase the proportional gain. and integral gain Adjust to a medium level to suppress potential overshoot while maintaining response speed.

[0101] When the temperature difference is "zero": the actual temperature is very close to the set value. The system will adjust the proportional gain. and integral gain The gain is reduced to the minimum level (but not zero), mainly relying on integral action to eliminate steady-state error, while minimizing system oscillations caused by excessive gain.

[0102] When the temperature difference is "positive small": the system will increase the proportional gain. and integral gain Symmetrically adjust to a moderate level similar to the "negative small" range to smoothly suppress positive deviations and prevent overshoot.

[0103] When the temperature difference is "positive": the system symmetrically and significantly increases the proportional gain. and integral gain This generates a strong control effect to quickly pull back the positive deviation.

[0104] This dynamic adjustment mechanism calculates the membership degree of temperature difference to each fuzzy set in real time, combines it with fuzzy logic operations, and outputs an optimized result after online defuzzification. and Parameters. This ensures that the system temperature can be stabilized quickly and smoothly under different operating conditions (such as sudden changes in fuel cell power or fluctuations in ambient temperature), effectively balancing response speed and steady-state accuracy.

[0105] Control b: with To achieve the target ratio, the refrigerant flow distribution ratio between the heat exchanger channel and the electric heater is controlled by adjusting the opening of the three-way valve. A feedforward-feedback composite control system is employed: feedforward control generates a baseline control command based on the target ratio; feedback control monitors the actual refrigerant flow rate in both the heat exchanger channel and the electric heater channel using a differential pressure flow meter, calculates the deviation between the actual and target flow ratios, and corrects this deviation using a PID controller, outputting a corrected control command. The baseline and corrected control commands are then superimposed to generate the final control command for controlling the flow path selection unit. This final control command drives the three-way valve, forming a closed loop that allows the system's actual flow distribution ratio to quickly and accurately approach the target ratio.

[0106] Fault backup mode: when When the refrigerant level is zero, approaches zero, or the proton exchange membrane fuel cell stack stops operating (shutdown / failure), the three-way valve spool switches to 0% opening, allowing the refrigerant to flow completely through the electric heater. A model predictive control algorithm is then used to regulate the output power of the electric heater. The predictive model of the model predictive control algorithm is a first-order inertial model of the electric heater. During the optimization process of the model predictive control algorithm, a constraint on the rate of change of the electric heater power is introduced, and the goal is to minimize the baseline driving heat. Temperature and power fluctuations during the transmission process are the optimization objectives.

[0107] Transfer function of a first-order inertial model for:

[0108] ;

[0109] in, For the Laplace operator, For model gain, It is a time constant;

[0110] Optimization objective function of model predictive control algorithm for:

[0111] :

[0112] in, To predict the time domain, To control the time domain, For the first The predicted temperature of the step, The set temperature for the refrigerant. For the first The change in power at each step and These are the weighting coefficients;

[0113] In the optimization solution, a strict power limit is imposed on the electric heater. (e.g. 1.2) ) and the upper limit of the rate of change of power (e.g., 50 W / s) to prevent equipment overload and safety issues such as flash evaporation of liquid refrigerant due to sudden power changes. Simultaneously, the system can complete mode switching and stabilize operation within 30 seconds of issuing a fuel cell shutdown command, while maintaining refrigerant temperature control accuracy within ±1℃.

[0114] This system also includes a sliding window covariance analysis module for real-time statistical analysis of the historical output power sequence of the exchange membrane fuel cell stack. This module maintains a data window of fixed length and identifies short-term trends (such as stable, increasing, or decreasing) in stack power by calculating the eigenvalues ​​of the covariance matrix of the power sequence within the window. Based on this analysis, the module can predict the fluctuation range of stack power over a future period (e.g., 15 minutes), providing a forward-looking basis for adjusting subsequent control strategies.

[0115] The flow path selection unit of this system uses a three-way valve, whose drive mechanism consists of a stepper motor, a multi-turn absolute encoder, and a reduction gear set. Through microstepping technology, the basic step angle of the stepper motor (1.8°) is further subdivided, and combined with a 1:50 reduction ratio, a valve position angle control accuracy of up to 0.1° is achieved. The mechanism has a response time of less than 0.3 seconds, ensuring both speed and accuracy in flow distribution.

[0116] This system is equipped with dual thermocouple redundant measurement units at key temperature measurement points (such as the refrigerant outlet). The acquired raw temperature signals are processed by a median filtering algorithm to effectively eliminate occasional pulse interference or abnormal sensor values, providing the controller with stable and reliable process variable input.

[0117] The exchange membrane fuel cell, circulating pump, heat exchanger, condenser, evaporator, electric heater, and expansion valve used in this invention are all existing known electrical devices, and all can be purchased and used directly on the market. Their structure, circuit, and control principle are all existing known technologies. Therefore, the structure, circuit, and control principle of the exchange membrane fuel cell, circulating pump, heat exchanger, condenser, evaporator, electric heater, and expansion valve will not be described in detail here.

[0118] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention used to illustrate the technical solutions of the present invention, and are not intended to limit the invention, nor are they intended to limit the patent scope of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. That is to say, any changes or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but whose technical problems are still consistent with the present invention, should be included within the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention to other related technical fields are similarly included within the patent protection scope of the present invention.

Claims

1. A proton exchange membrane fuel cell waste heat recovery ejector refrigeration system, characterized in that, include: The fuel cell thermal management subsystem has an internal coolant circulation system to absorb and transfer the waste heat generated by the proton exchange membrane fuel cell stack. The ejector refrigeration subsystem has a refrigerant circulating internally as the working fluid. The ejector refrigeration subsystem is thermally coupled to the fuel cell thermal management subsystem through a heat exchanger (3) to receive the transferred waste heat to drive the refrigerant and generate a refrigeration effect. The ejector refrigeration subsystem also includes a flow path selection unit (5) and an auxiliary heating unit (6). The flow path selection unit (5) adjusts the flow path of the refrigerant so that the refrigerant can selectively receive waste heat from the fuel cell thermal management subsystem or receive supplementary heat from the auxiliary heating unit (6) to drive the refrigerant and maintain a stable output of the refrigeration effect. The fuel cell thermal management subsystem includes a coolant circulation pump (1), a proton exchange membrane fuel cell stack (2), and a heat exchanger (3) connected by a first pipeline. The ejector-type refrigeration subsystem includes a refrigerant circulation pump (4), a second flow channel of a heat exchanger (3), an ejector (7), and a condenser (8) connected by a second pipeline. The flow path selection unit (5) and the auxiliary heating unit (6) are connected in series. The series structure formed by the flow path selection unit (5) and the auxiliary heating unit (6) is located between the refrigerant circulation pump (4) and the ejector (7), and is connected in parallel with the second flow channel of the heat exchanger (3). The flow path selection unit (5) is a three-way valve; the inlet of the three-way valve is connected to the outlet of the refrigerant circulation pump (4), the first outlet is connected to the inlet of the second flow channel of the heat exchanger (3), and the second outlet is connected to the inlet of the auxiliary heating unit (6); The outlet of the second flow channel of the heat exchanger (3) and the outlet of the auxiliary heating unit (6) are connected together through pipelines and then connected to the primary flow inlet of the ejector (7). The outlet of ejector (7) is connected to the inlet of condenser (8). The outlet of condenser (8) is divided into two paths: one path is connected to the inlet of evaporator (10) through throttling device (9); the other path is connected to the inlet of refrigerant circulation pump (4); the outlet of evaporator (10) is connected to the secondary flow inlet of ejector (10).

2. The proton exchange membrane fuel cell waste heat recovery ejector refrigeration system according to claim 1, characterized in that, The auxiliary heating unit (6) is an electric heater, and the throttling device (9) is an expansion valve.

3. The proton exchange membrane fuel cell waste heat recovery ejector refrigeration system according to claim 1, characterized in that, The ejector (7) includes a nozzle (71), a suction chamber (72), a mixing chamber (73), and a diffusion chamber (74) connected sequentially along the fluid flow direction. The nozzle (71) has an inlet that forms the primary inlet of the ejector (7), and the side wall of the suction chamber (72) has a secondary inlet of the ejector (7).

4. The control method for the proton exchange membrane fuel cell waste heat recovery ejector refrigeration system according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Based on the operating parameters and coolant parameters of the proton exchange membrane fuel cell stack (2), determine the waste heat output of the proton exchange membrane fuel cell stack (2); establish a state observation model integrating the thermal dynamics of the proton exchange membrane fuel cell stack (2) and the time-varying heat transfer efficiency of the heat exchanger (3), and estimate and correct the current effective waste heat output transferred from the waste heat output through the heat exchanger (3) online by introducing a feedback correction term that includes the temperature of the proton exchange membrane fuel cell stack (2), the coolant flow rate and the temperature difference on both sides of the heat exchanger (3). ; S2. The current effective waste heat output... With reference driving heat set according to cooling demand Real-time comparison is performed, and based on the comparison results, the system adaptively switches between the following three working modes, and performs corresponding coordinated control by coordinating the fluid path allocation of the flow path selection unit (5) and the power output of the auxiliary heating unit (6): Rated operating mode: When At the same time, the flow path selection unit (5) controls the refrigerant to flow completely through the second flow path of the heat exchanger (3), and uses a PI controller to adjust the refrigerant circulation flow rate to match the waste heat output, while shutting down the auxiliary heating unit (6). Low power compensation mode: when At that time, calculate the heat deficit. , The following two controls are executed in parallel: Control a: Based on heat deficit The deviation between the actual temperature and the target temperature of the refrigerant is used to dynamically adjust the output power of the auxiliary heating unit (6) using a fuzzy PID algorithm; Control b: with To achieve the target ratio, the flow distribution of refrigerant between the heat exchanger (3) and the auxiliary heating unit (6) is controlled by adjusting the opening degree of the flow path selection unit (5), and feedback correction is performed based on the monitoring of the flow after distribution, so that the actual distribution ratio approaches the target ratio. Fault backup mode: when When the refrigerant is zero, approaches zero, or the proton exchange membrane fuel cell stack (2) stops working, the control flow path selection unit (5) ensures that the refrigerant flows completely through the auxiliary heating unit (6), and uses a model predictive control algorithm to adjust the output power of the auxiliary heating unit (6). The prediction model of the model predictive control algorithm is the first-order inertial model of the auxiliary heating unit (6). In the optimization solution process of the model predictive control algorithm, the power change rate constraint of the auxiliary heating unit (6) is introduced, and the minimum reference driving heat is minimized. Temperature and power fluctuations during the transmission process are the optimization objectives.

5. The control method for the waste heat recovery ejector refrigeration system of a proton exchange membrane fuel cell according to claim 4, characterized in that, The state observation model is a Luneburger observer. The feedback correction term includes the residual consisting of the difference between the actual measured outlet temperature of the proton exchange membrane fuel cell stack (2) and the temperature estimated by the observer. After weighting the residual by the designed observer gain matrix, it is fed back into the state observer model to dynamically correct the current effective waste heat output. The estimated value.

6. The control method for the waste heat recovery ejector refrigeration system of a proton exchange membrane fuel cell according to claim 4, characterized in that, In control b of the low-power compensation mode, a composite control strategy combining feedforward and feedback control is adopted for the refrigerant flow distribution process; wherein: Feedforward control generates a reference control command based on the target ratio; Feedback control is based on real-time monitoring of the actual allocation ratio, calculating the deviation between the actual allocation ratio and the target ratio, and correcting the deviation through a PID controller to output a correction control command. The baseline control command and the correction control command are superimposed to generate the final control command for controlling the flow path selection unit (5).

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