Abstract
Multiphase systems are nowadays considered for various industrial applications. Numerous pulse width modulation (PWM) schemes for multiphase voltage source inverters with sinusoidal outputs have been developed, but no detailed analysis of the impact of these modulation schemes on the output peak-to-peak current ripple amplitude has been reported. Determination of current ripple in multiphase PWM voltage source inverters is important for both design and control purposes. This paper gives the complete analysis of the peak-to-peak current ripple distribution over a fundamental period for multiphase inverters, with particular reference to seven-phase VSIs. In particular, peak-to-peak current ripple amplitude is analytically determined as a function of the modulation index, and a simplified expression to get its maximum value is carried out. Although reference is made to the centered symmetrical PWM, being the most simple and effective solution to maximize the DC bus utilization, leading to a nearly-optimal modulation to minimize the RMS of the current ripple, the analysis can be readily extended to either discontinuous or asymmetrical modulations, both carrier-based and space vector PWM. A similar approach can be usefully applied to any phase number. The analytical developments for all different sub-cases are verified by numerical simulations.
Highlights
Multiphase motor drives have many advantages over traditional 3-phase motor drives
The analytical expression of peak-to-peak current ripple amplitude has been derived in the whole fundamental period as function of the modulation index by identifying four different relevant cases and some sub-cases
A simplified expression to evaluate maximum of the current ripple amplitude in the fundamental period is given
Summary
Multiphase motor drives have many advantages over traditional 3-phase motor drives. Most important are the ability to reduce the amplitude and to increase the frequency of torque pulsations, to reduce the rotor harmonic current losses and to lower the DC link current harmonics. The importance of the peak-to-peak current ripple evaluation, in addition to the RMS analysis, was recently recognized in [20], where the ripple amplitude is investigated for 3-phase PWM inverters. With adaptive compensation are studied in [22] and [23] as well, where the knowledge of peak-to-peak current ripple was of interest, but it has not been properly addressed Another example of application is referred to hysteresis current controllers and variable switching frequency PWM, for single-phase [24]. Despite the numerous PWM schemes for 7-phase VSIs with sinusoidal outputs have been developed, no detailed analysis of the impact of these modulation schemes on the output peak-to-peak current ripple amplitude has been reported. A complete analysis of output current ripple is developed in this paper for 7-phase PWM inverters, with reference to centered and symmetrical switching patterns generated either by CB- or SV-PWM. Simulation results are directly comparable to the analytical developments, expecting a very precise matching
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