The modelling, control, switching schemes, novel applications, etc. of multi-phase voltage source inverters (VSIs) have been studied in recent years. While some DC-link capacitor considerations have been reported and ripple current assessments presented, the impact of these analyses on system design has not previously been quantified. These knowledge boundaries are expanded via this research. Meanwhile, a hypothesis is proposed that under the equitable operating conditions, the increase in the phase number decreases the DC-link capacitor requirements compared with the representative conventional three-phase VSIs. The analytical study shows the results corresponding to the hypothesis. Moreover, another hypothesis is made that other factors, e.g. switching strategies, carrier waveforms, and interleaving techniques also determine the DC-link capacitor requirements, and some strategies can further decrease the DC-link capacitor requirements. The presented analytical study supports this hypothesis. The study is partially validated via experiments on a brushless permanent magnet synchronous motor (PMSM) drive system designed for the equitable comparison of three- and nine-phase VSIs driving PMSMs. Finally, the DC-link capacitor design procedure is proposed for two level multi-phase VSIs.