الفهرس 
Chapter 1Only 14 pages are availabe for public view
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Abstract
The load characteristic of a dc converter is linearized by using fuzzy compensation. The dc to dc converter (chopper) output voltage is controlled using a pulse width modulated signal applied to the gate of an insulated Gate Bipolar Transistor (IGBT) after appropriate conditioning. A systematic study of the chopper load characteristics was conducted. This study highlighter 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, using MATHCAD, was conducted to determine the amount of nonlinear compensation required to linearize the road 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 were fuzzified using the fuzzy tool box under MATLAB. A fuzzy rule base was constructed using two input universes of discourse: the load current and the original duty cycle K. the output universe of discourse is the negative offset of the duty cycle. Off-line and on-line compensation schemes were successfully tested, and the results are validated.
A micro-computer provided with a data acquisition card is used to perform the following functions:
(1) The control of the chopper duty cycle.
(2) The provision of a current limit with hystresis to protect the chopper.
(3) On-line fuzzy compensation.