Sylvain Lemofouet

A Hybrid Energy Storage System Based on Compressed Air and Supercapacitors With Maximum Efficiency Point Tracking (MEPT)

In addition to the high-capacity storage facilities based on hydropower technologies, electrochemical solutions are todays candidate for storage for renewable energy sources support. However, sustainability and limited life cycles of batteries are often inhibiting factors. This paper presents a hybrid energy storage system with high life cycle, which is mainly based on compressed air, where the storage and discharge are done within maximum efficiency conditions. As the maximum efficiency conditions impose the level of converted power, an intermittent time-modulated operation mode is applied to the thermodynamic converter to obtain a variable converted mean power. A smoothly variable output power is achieved with the help of a supercapacitive auxiliary storage device used as a filter. This paper describes the concept of the system, the power-electronic interface circuits, and especially the maximum efficiency point tracking (MEPT) algorithm and the strategy used to vary the output power. In addition, this paper presents the characteristics of high-efficiency storage systems where the pneumatic machine is replaced by an oil-hydraulic and pneumatic converter, which is used under isothermal conditions. Practical results are also presented, which are recorded from a low-power pneumatic motor coupled to a small dc generator as well as from the first prototype of the final hydropneumatic system

Hybrid energy storage systems based on compressed air and supercapacitors with maximum efficiency point tracking

Beside the high-capacity storage facilities based on hydro-power technologies, electrochemical solutions are the todays candidate for storage for renewable energy sources. However, limited life-cycles and sustainability of batteries are often inhibiting factors. This paper presents a hybrid energy storage system with high life cycle, based on compressed air energy storage (CAES). The storage and discharge are done within maximum efficiency conditions. As the maximum efficiency conditions impose the level of converted power, an intermittent time-modulated operation mode is applied to the thermodynamic converter to obtain a variable converted power. A smoothly variable output power is achieved with the help of a supercapacitive auxiliary storage device used as a filter. The paper describes the concept of the system, the power-electronic interface circuits and especially the maximum efficiency point tracking (MEPT) algorithm and the strategy used to vary the output power. In addition, the paper describes the principles of higher efficiency storage systems where the air machine is replaced by an oil hydro-pneumatic converter, used under isothermal conditions. Practical results are reported, that have been recorded from a low-power pneumatic motor coupled to a small DC generator for the purely pneumatic system, and from a first prototype of the oil-hydraulics and pneumatic system. Some economical considerations are also made, through a comparative cost evaluation of the presented hydro-pneumatic systems and a lead acid batteries system, in the context of a stand alone photovoltaic home application. This evaluation confirms the cost effectiveness of the studied hybrid storage systems