Research On Impedance Measurement Scheme Of Fuel Cell System Based On Parameter Identification

As our country "carbon emissions peak and carbon neutralization" strategy continues to advance,clean energy quickly rises and develops rapidly.Fuel Cell System as a high efficiency,zero emission of hydrogen and electric transformation technology carrier.It’s the core industry of realizing our hydrogen energy strategy,promote energy revolution and low carbon transportation.The on-line detection of internal state information,such as power characteristics and water content,can better analyze the mechanism of Fuel Cells,which is of great significance to extend the service life of the system and improve the output efficiency of the system.However,when the Fuel Cells System is running,the internal water content and other parameters can’t be directly measured.By means of online measurement and derivation analysis of the internal impedance of the Fuel Cells,the working state of the system can be mapped,so as to achieve the purpose of indirect monitoring of the system.This paper takes the Proton Exchange Membrane Fuel Cells power generation system as the research object,and focuses on the impedance measurement of Fuel Cells.Two kinds of online impedance measurement schemes based on load disturbance and excitation signal injection are discussed.Combining the influence of the measurement accuracy,anti-noise characteristics and power consumption of the two schemes,the more suitable impedance measurement scenarios of the two schemes are analyzed.In order to achieve the online impedance measurement of Fuel Cells,the main research content of this paper is summarized as follows:1.According to the working principle of the Fuel Cell,the output voltage model is established.The activation loss,ohmic loss and concentration loss of the reactor are compensated into the open-circuit voltage of the Fuel Cell,which is used as the terminal output voltage.After that,the model of the DC-DC converter in the system is built.The Boost function of the DC-DC converter is realized through the Boost circuit,and the duty cycle of the boost circuit is adjusted to realize the function of adding AC disturbance to the output current of the Fuel Cell Stack.According to the established model,a Fuel Cell Impedance measurement simulation platform is established in the Simulink environment.Through the simulation platform,the subsequent impedance measurement scheme is verified.2.An impedance measurement scheme based on load disturbance is designed.By adjusting the output current of the reactor by the DC-DC converter,the excitation addition of the reactor is realized.The Randles circuit is used to describe the electrochemical reaction of the Fuel Cell.The reactor is described as an ideal voltage source and Randles circuit in series.The impedance measurement is translated into the identification of unknown parameters of the equivalent circuit.Then a circuit model oriented to parameter identification is established,and a parameter identification scheme based on Recursive Least Square method is designed.The impedance of Fuel Cell was derived by identifying unknown parameters in the model.Finally,the effectiveness of the scheme is verified on the Fuel Cell Impedance measurement simulation platform and the power required to generate AC disturbance is analyzed.3.An online impedance measurement scheme based on excitation signal injection is designed.When the Fuel Cell System is working,the measurement scheme that generates excitation to the reactor through load disturbance will cause the fluctuation of the stable operating point of the Fuel Cell,and there are some problems such as poor noise suppression effect and large fluctuation of instantaneous power consumption.Therefore,an improved scheme of adding AC power outside the Fuel Cell System is proposed,and the AC signal generated by it is used as the excitation of the reactor.In this paper,the measurement circuit is designed for the excitation impedance measurement scheme,and the circuit state space equation model oriented to parameter identification is established.The unknown state variables in the state space equation are identified based on Kalman filter algorithm,and the unknown parameters of Randles circuit are derived backwards to realize the online impedance measurement.Finally,the scheme is verified on the Fuel Cell Impedance measurement simulation platform and the power consumption of the excitation power source is analyzed..