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Abstract
The load characteristics of a dc to dc converter are linearized by using both off-line fuzzy compensation technique and on-line fuzzy compensation technique. The dc to dc converter (chopper) output voltage is controlled using a pulse width modulated signal applied to the gate of switching device after appropriate conditioning. A systematic study of the chopper load characteristics is conducted. This study highlights the problem of discontinuous conduction encountered with chopper fed dc drives and switch mode power supplies under light loads. The problem resides in the nonlinear increase of the output voltage (and speed in drive applications) as the load current drops below a critical value that depends on the chopper duty cycle K.
An analytical study is conducted to determine the amount of nonlinear compensation required to linearize the load characteristics. This compensation takes the form of a negative offset of the chopper duty cycle K to maintain a constant output voltage equal to that obtained under continuous conduction. The application of this crisp compensation in the form of a lookup table requires considerable memory and. interpolation is unavoidable. To circumvent these difficulties the compensation values are fuzzified using the fuzzy toolbox under MA TLAB. A fuzzy rule base is constructed using two input universes of discourse: the load current (fa) and the original duty cycle (K). The output universe of discourse is the negative offset of the duty cycle (L\K). Off-line and on-line fuzzy compensation techniques are programmed by ’C’ language and ruris through a microcontroller. Off-line and on¬line fuzzy compensation schemes are successful]y tested, and the results are validated experimentally.