Intensive random carrier pulse width modulation for induction motor drives based on hopping between discrete carrier frequencies

The existing random carrier pulse-width modulation (RCPWM) schemes result in poor non-deterministic characteristics. They basically use a single-frequency triangular carrier and its inverted version to synthesise the random carrier by a pseudo-random binary sequence (PRBS) bit selector. Even though the bits are highly random in nature with large pattern repetition rate, the resulting random carrier does not possess required level of randomness. Rather it can make slight positional variation in the resulting PWM pulses. Moreover, the harmonic spreading effects of these randomness may not be sufficient to meet the expectations of modern drives. Hence, this study proposes a multiple carriers based RCPWM (MCBRCPWM) scheme for the voltage-source inverter fed induction motor drive to enhance the harmonic power spreading ability of the modulator. The proposed MCBRCPWM scheme utilises the non-deterministic characteristics of both the PRBS and hopping action between the MCs involved. The simulation results using MATLAB 7.1.0 (2010a)-Simulink software and the experimental results with hardware implemented using XC6SLX45 field programmable gate array for a 3Ø squirrel cage induction motor load prove the excellent harmonic spectra spreading capability of the proposed scheme as compared with existing non-deterministic methods.