On-line fuzzy compensation technique applied on the load characteristics of a dc to dc converter using microcontroller

This paper highlighted the problem of discontinuous conduction encountered with chopper fed dc drives under light loads using on-line fuzzy compensation technique. As the load current drops below a critical value depending on the duty cycle (K), there is a nonlinear increase in output voltage. An analytical study was conducted to determine the amount of nonlinear duty cycle compensation required to linearize the load characteristics. The duty cycle compensation offset (¿K) takes the form of a negative value 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 were fuzzified. A fuzzy rule base was constructed using two input universes of discourse: the armature current (I_a)and the original duty cycle (Y.). The output universe of discourse is the negative offset of the duty cycle (¿K). An AVR Atmega 8535 is used to control the chopper duty cycle and perform on-line fuzzy compensation. On-line fuzzy compensation schemes were tested, by using simulation and validated experimentally.