Research And Design Controllable AC Current Source For Fuel Cell Impedance Monitoring

In the PEMFC system,impedance of the fuel cell is not only the main signs which measurses the situation of the proton and electron transfering,but also decided to stack the key parameters of power generation efficiency.Real-time measurement impedance of fuel cell show the real-time access dynamic information,enhance understanding and analysis of the fuel cell reaction mechanism,has very important significance to improve fuel cell durability and life.In the fuel impedance on-line monitoring system,the controllable AC current source as a source of excitation is particularly critical.This dissertation gives a current source system design which takes DSP as a controller,and through the joint regulation of the DC/DC and DC/AC two-level-power transform to achieve high accuracy,wide range of frequency conversion amplitude-change sinusoidal current output.The output current parameter is set by the main control board of internal impedance test which is connecting network through communication interface.The main content is as follows:Discuss the various components of the current source syetem overall,make a control programme which achieves stable current output by using voltage inverter bridge,and prove the feasibility of the programme by equivalent analysis of voltage inverter bridge.According to the ease of digital effects,the quality of output and the comparative analysis of the two classic SPWM modulation,we adopt the unipolar SPWM modulation and research the control algorithm at the same time.According to specific requirements of current source system,we have given the structure diagram of hardware of the system,and also built a modular hardware platform,including the control module,DC/DC power modules,inverter modules, communication module,protect module and the auxiliary power part.It has concretely finished each module hardware design.On the basis of inverter model in the main circuit,it has established a dual-current closed-loop control model,The simulation results show that current dual-loop control has a good stability and dynamic response.Researching from the traditional continuous PID control to the discrete incremental PI control,it has designed a DSP-based and integral saturated in part incremental digital PI controller.The current source system software design based on DSP controller has been finished,and we especially conducts the analysis research of software design's several important links.Carried on the current source system's experiment,the experiment show that the control system has basically achieved the control requirements above-mentioned,and obtained better control effect.