| The impedance measurement of fuel cell is the key to the application of fuel cells in the automotive field.In recent years,the impedance measurement method based on DC/DC ripple modulation has been widely concerned by scholars at home and abroad,but the tracking performance and stability performance of conventional control strategy are poor.And it is impossible to accurately track high-frequency signals,resulting in large errors in impedance measurement results.Therefore,this paper proposes adaptive passive control as the control strategy of DC/DC converter in impedance measurement system.Compared with conventional control and traditional passive control,this new strategy improves the tracking capability and adaptive capability of DC/DC converter,which is more in line with the frequently changing usage of the load.The main research contents of this paper are as follows:The scheme of each link in the internal resistance test system is analyzed and the overall test scheme of the system is designed.According to the requirements of internal resistance test,Boost circuit is selected as the main circuit structure.In order to improve test efficiency and control accuracy,triangular wave is selected as modulation signal.Finally,an overall scheme of fuel cell impedance measurement is designed.The passive control model of DC/DC converter is derived from the Euler – Lagrange(EL)model.The working principle of DC/DC converter for fuel cell impedance measurement system is analyzed,and the EL mathematical model of DC/DC converter is established.At the same time,the small signal ac model of DC/DC converter is derived by using the idea of linearization.Furthermore,the stability of the DC/DC converter is analyzed by using the small signal model.An adaptive passive control strategy for DC/DC converter is proposed,which makes up for the deficiency of conventional control in tracking high frequency signals.The convergence rate of the energy function is improved by injecting damping into the dissipated energy of the system.The linear estimation matrix is used to estimate the load parameters in the controller,which improves the adaptive ability of passive control.What's more,the feasibility and superiority of adaptive passive control in impedance measurement are verified by comparing simulation with conventional control.The physical platform is built to verify the impedance measurement scheme and the adaptive passive device.The comparison experiment of adaptive passive control and EIS measurement of fuel cell impedance measurement is carried out on the physical platform.The experimental results show the feasibility of the impedance measurement scheme.At the same time,it is confirmed that adaptive passive control is more accurate than conventional control EIS curve fitting results in the impedance measurement system,indicating the advantages of adaptive passive control in the field of impedance measurement. |
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