A Tripartite Random Pulse Width Modulator for Efficient Distribution of Harmonic Power in High Power AC Drives

  • S.Senthamil Selvan


The incessant research effort on variable speed AC drives has resulted several
performance enhanced pulse width modulation (PWM) strategies with improved features
like the efficient exploitation of DC link voltage, the reduced voltage total harmonic
distortion (THD), the ease of filtering, lesser switching losses etc. The radical
contemplation reveals that the intricacy prevails in the harmonic spreading savvy, and
the remnant task of distributing the harmonic power in the PWM strategies has not been
addressed to the fruition, hitherto. The random PWM (RPWM) schemes are successful in
reducing the harmonic spread factor (HSF) significantly, whilst to retain the basic
metrics, the tenet of introducing randomness to be amalgamated with the high
performance deterministic PWM strategies. This research paper suggests an inventive
RPWM, a tripartite RPWM (TRPWM), wherein both the random position and random
carrier abilities pervade to the pristine space vector PWM (SVPWM) to invigorate the
harmonic power spreading feature in the three phase voltage source inverter (VSI) fed
induction motor drive system. The reference waves are obtained by the time calculation
of states in respective sectors of the space vector diagram. The initial carrier selection
amid the four triangular carriers is done using two pseudo random binary sequence
(PRBS) generators. As a sequel of this randomized carrier generation, the gating pulses
are generated by comparing with reference signals, and finally, the positional
randomization is incorporated using a third PRBS. A formulaic investigation on the
harmonic spreading ability of the pristine SVPWM, the SVPWM with single randomness,
and the suggested TRPWM is performed in MATLAB/Simulink platform. Further the
experimental corroboration is done in a proof-of-concept (POC) prototype, with the
patronage of a SPARTAN-6 (XC6SLX45) FPGA processor, an IGBT based three phase
VSI and a 2.2kW, 14Nm induction motor.