Random slope PWM inverter using existing system background noise: analysis, design and implementation

Random slope PWM (RSPWM) is one of the most easily realised RPWM techniques for reducing the acoustic noise due to PWM switching harmonics. However, it is difficult to analyse it in closed form and it is thus difficult to design quantitatively. The development of an RSPWM inverter using existing system background noise and its applications are presented. First, the effects of the random signal’s attributes on the harmonic spectrum distributed characteristics of the RSPWM inverter output are observed intuitively. Then according to the observed phenomena, a quantitative design procedure is derived through using the equivalent instantaneous frequency change concept. For the ease of implementation, the random signal used for random slope modulation is extracted from the current traclung control error signal with suitable filtering. Finally, the realisation of the designed RSPWM scheme using a commercially available voltage-controlled oscillator integrated circuit is achieved. The designed RSPWM inverter is employed to power an induction motor drive, and its effectiveness is demonstrated experimentally.