Optimization of the Repeated PWM Command Applied to the Variable Voltage Variable Frequency 'VVVF' Converter

Abstract

A new technique of generation signals of the RPWM (repeated pulse width modulation) command have been proposed, by using an alternated and variable repetition of data segments of a reference PWM signal applied. The mathematical aspects and the spectral analysis of this technique are presented as well as the hardware to concretise it. So a optimise concept of this generation will be presented, based independently on the generation of signals command of micro-controller in the aim to reduce the time allocated by this last and to minimise the number of addresses lines between the micro-controller and the memory. General TermsPulse width modulation.

Improving of the Generation Method of Repeated PWM Based on the Signals Combinations Applied to a PV Pumping System

“…The problem found in the simple repetition technique (RPWM) is the step frequency variation of the command signal that becomes important in the interval of 50 Hz (Example we cannot generate a frequency between 48.23 Hz and 50.08 Hz [17]). To increase the frequency of data generation witch increases the frequency of modulation and losses by commutations, or to decrease the number of data of segments (Equation n° 4), is regulated by a generation of signals based on the alternated repetition of data segment, i.e.…”

“…In this technique each segment "i" is repeated with a different value R i of other segments in order to improve the pace of change in frequency and accuracy in the generation of signals [17]. …”

“…To produce a signal of low frequency (relatively to the frequency of the reference signal), we produce a sequence of repetitions of each n time segment [16,17]. The number of repetition is calculated in such a way to get the frequency required by the system for maintained V/F constant.…”

“…Each segment will be converted in an impulse duty cycle that determines the instantaneous amplitude. Each impulse is converted in a numeric shape of n bits to represent the closing and opening state of switches related to the three phase power bridge (t on , t off ) [15,17]. In Fig.…”

“…The application of the repetition technique of data segments of a sampled reference signal RPWM (Repeated Pulse Width Modulation) has given several benefits such as increasing the number of switching periods [15,17], the improvement of the spectrum by the rejection of harmonics to higher frequencies, therefore the range of frequency variation, improving the current wave and provide a highly optimized control or level of memory [18]. In addition, the technique of robin ARPWM (Alternate Repeated Pulse Width Modulation) allows us to reduce the increment step and improve the loss factor.…”