Extending 2-D space vector PWM for three-phase four-leg inverters

This paper proposes a novel Space Vector Pulse Width Modulation strategy extending conventional 2-D SVPWM strategies for its use in three-phase four-leg inverters. The methodology is based on the segregation of the zero sequence from any initial desired unbalance voltage set-points. In this way, the operation of the fourth leg is reserved to manage the desired homopolar component and to compensate for the inherent homopolar component provided by any 2-D SVPWM technique. This choice not only minimizes the complexity and effort to determine the location of the reference voltage space vector from a 3-D to a 2-D space but also enables to use 75% of the affordable space to synthesize voltages under a 3-D SVPWM technique. Furthermore, the proposal is compared with other four 3-D SVPWM techniques analysing the advantages in terms of execution time, memory program, simplicity and neutral to mid-point voltage quality, resulting into a really good implementing alternative compared with the major 3-D SPVWM techniques analysed. The new modulation strategy is presented in detail, and a complete set of simulations using this particular modulation strategy has been done, and the results of these simulations have been validated on a laboratory set-up using a four-leg inverter.