A hybrid PWM strategy for multilevel voltage source inverters

This paper proposes a simple pulse width modulation (PWM) method for multilevel inverters. It takes advantage of the fact that the Space Vector PWM switching sequences for a multilevel inverter are the same as those created by the Carrier-based PWM when an adequate zero sequence component is injected into the carrier system references. The paper introduces a generalized equation for the zero sequence component, which is a function of a "broad sense" distribution ratio of zero voltage vectors. This allows for the pulse widths to be easily calculated for any number of levels (inclusive two). The method dispenses with the complicated derivation of similar relations for inverters with more than three levels. It can also be applied to determine the switching pattern that minimizes the switching losses when the load phase angle is taken into account. Simulated and experimental results verify the validity of the proposed technique.