Ultracapacitor integration for short-term energy management in a hybrid system

Purpose - This paper aims to deal with the integration of energy storage devices (ultracapacitors) in wind energy applications to absorb the short terms fluctuations. The originality of this contribution is focused on energy management related to wind power frequency distribution between the hybrid sources. The robust and simplified control strategies are proposed and applied to DC-DC converters without AC signals measurements. A novel MPPT method is introduced to operate the wind generator at the maximum power regardless of the wind speed variations. The fluctuating part of this power is mitigated by using a UC. The reference current of this last is obtained from a low pass filter. An innovative limitation algorithm of the UC voltage is proposed with aims to ensure optimal operation of the system. The control algorithms are implemented in a PIC18F4431 microcontroller. Some experimental results from this new approach are presented and analyzed. Design/methodology/approach - This study is organized according to the following main and sub-topics after introduction: frequency distribution principle; wind energy generation; short-term fluctuations storage system; and experimental setup and results. Findings - The simulations results highlight the interest of using ultracapacitors in a wind-diesel system. The experimental results show that the short term fluctuations induced by the wind generator current are effectively mitigated by the ultracapacitors. Originality/value - In this paper, an interesting MPPT method is presented. The fluctuations mitigation is realised by using the frequency distribution according to ultracapacitors dynamics. The ultracapacitors voltage control method is proposed with the aim of maintaining optimal operation conditions, and is validated by experimental tests.