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Keywords: lead-acid battery, Stand-alone Natural Energy Power System (SNEPS), prolonging of service life, Electric Double Layer Capacitor (EDLC), bi-directional compensation system, electric power smoothing In Stand-alone Natural Energy Power System (SNEPS) with power energy-storage device, power fluctuation in short period is one of the main reasons that recharge cycle times increases and lead-acid battery early failure. Hence, this paper proposed a electric power smoothing method for lead-acid battery of SNEPS using bidirectional Buck/Boost converter and Electric Double Layer Capacitor (EDLC), in order to prolong the service life of lead-acid battery through suppressing the power fluctuation. The validity of proposed system is confirmed by frequency characteristics analysis result and experimental results of actual WTG power system. In current study, as a example, The frequency region of 0. A smoothing precision is defined to evaluate the smoothing level of power fluctuation suppressing. Here, the output voltage of battery is approximated constant, the electric power smoothing is considered by considering the output current smoothing. As a result, the smoothing precision is given in (1). We purpose to gain the smoothing precision of smaller than 10%. Smoothing Precision =Current Fluctuation of Lead − acid Battery Current Fluctuation of Natural Energy Power Supply Fig. 1 shows the configuration of the proposed system. Where an EDLC is connected with lead-acid battery in parallel as the hybrid energy storage device, based on charge/discharge of EDLC, EDLC compensates the harmonic component of power fluctuation of short period by controlling the bi-directional converter, in order to supply smooth component to battery. A proportional & integral (PI) controller is adopted to control and adjust the steady state error ∆ib (∆ib = ib re f − ib) of reference and battery current tend to zero. The simulation result of stable operation of the proposed system is shown in Fig. 2. Fig. 2 shows the current fluctuation, is is suppressed and smoothed current, ib is supplied to battery. However, the nonlinear phenomenon results in the characteristics analysis of system that using conventional perturbation analysis theory becomes complex and difficult. Hence, parameters that satisfy electric power smoothing output are selected in the stable region during system design using PSIM software and the effect trend-line. Fig. 3 shows the calculation results and experimental results of frequency characteristic of the proposed system. The results satisfy the requirement of smoothing precision in the defined frequency target region. In addition, the validity of the proposed system is confirmed in actual stand-alone WTG power system too, the experimental results are shown in Fig. 4. Ryosuke Shibata * Student MemberNaoki Yamamura * MemberMuneaki Ishida * MemberTo resolve energy shortage and global warming problem, renewable natural resource and its power system has been gradually generalizing. However, the power fluctuation suppressing in sho...

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