| The output power of photovoltaic power generation system has the disadvantage offluctuation, so the energy storage device must be used to ensure the stability of the system.The frequently fluctuation of the system will shorten the lifetime of the battery. So thetraditional battery energy storage system can not satisfy the develop requirements ofenergy storage system. As a new energy storage component, ultracapacitor has a lot ofgood characteristics, such as high power density and long cycle life. In this paper, theenergy management strategy and the control method of converters of theultracapacitor-battery hybrid energy storage system(HESS) in stand-alone photovoltaicpower generation system are mainly discussed.In this paper, the advantages of HESS used in stand-alone photovoltaic system areanalyzed. And then according to the different characteristics of photovoltaic cells,ultracapacitor and battery, a new energy management strategy is studied to coordinate therelationships among the three power sources. The ultracapacritor is used to restrain thefluctuation, which can make the fullest use of quick reaction ability of the ultracapacritor.The battery is used to store the surplus energy through constant current charge anddischarge to maintain the power balance of the system According to the different workingconditions of photovoltaic cells and hybrid energy storage system, the three converterswork in different modes and the three power sources coordinating to ensure the stablenessof the system. The energy management strategy is verified through MATLAB simulationmethod, the results show that the hybrid energy storage system can maintain the stabilityof the dc-bus voltage when the load or the output power of the cells is changed. When theoutput power fluctuation is small, the battery is not used, thus will reduce the frequency ofcharge and discharge of the battery.The converter has the problems of time-variance and nonlinearity, which will producebad influences to the performance of the converter. The synergetic control is proposed tosolve these problems. A unified synergetic controller is designed to maintain the dc-busvoltage. A constant current synergetic controller is designed to regulate the discharge and charge of the battery. The MATLAB simulation results verified the excellent performanceof the proposed control method.An experimental platform of the system is built in the laboratory. The energymanagement strategy and control method are established in the experiment and the resultsillustrate the effectiveness of the energy management strategy. The results show that thestrategy mentioned in this paper not only can guarantee the stability of the dc-bus voltage,but also can extend the battery life significantly, at the same time, the efficiency ofultracapacitor is improved especially. |
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