Switching period randomisation for multilevel converter modulation

• Published in: 2015 IEEE 11th International Conference on Power Electronics and Drive Systems pp. 975 - 980
• Main Authors: Walker, Geoffrey R., Ledwich, Gerard F.
• Format: Conference Proceeding Journal Article
• Language: English
• Published: IEEE 01-06-2015
• Subjects: Amplitude modulation; Carriers; Frequency conversion; Harmonic analysis; MATLAB; Modulation; Pulse duration modulation; Pulse width modulation; Sidebands; Spectra; Spreads; Switches; Waveforms
• ISSN: 2164-5256; 2164-5264
• DOI: 10.1109/PEDS.2015.7203508

The spectral energy associated with the carrier and sidebands of naturally sampled carrier based PWM can be spread by randomising the carrier (switch) half-period T c = 1/2f c . So long as the switch duty cycle each period still correctly reflects the value of the modulating fundamental waveform as sampled during that switch period, then the fundamental component will remain undistorted. Natural sampling will ensure this occurs. Carrier based PWM can be extended to (m+1) level multilevel converter waveform generation by creating m triangular carriers, each with an equal 2π/m phase displacement. Alternatively the carrier disposition strategy calls for m amplitude displaced triangular carriers, each of amplitude 1/m and frequency mf c . Randomising these carrier sub-periods T 0 = 1/2mf c is shown to generate (m+ 1) level PWM waveforms where the first (m-1) carrier groups are cancelled, while the remaining carrier and sidebands at multiples of mf c are spectrally spread. Numerous five level simulation and experimentally gathered randomised PWM waveforms are presented, showing the effects of the variation of the degree of randomisation, modulation depth and pulse number.