A simple and generalized space vector PWM control of cascaded H-bridge multilevel inverters

This paper presents an automatic switching pattern generation for multilevel cascaded H-Bridge inverters with equal dc voltage sources, based on the space-vector pulse width modulation (SVPWM) techniques. The proposed switching strategy generates a voltage vector with very low harmonic distortion and reduced switching frequency. This new control method is an attractive alternative to the classic multilevel pulse width modulation techniques considering the following aspects, mainly, minimization of voltage and current total harmonic distortion (THD), extension of range of linear operation; and least number of commutations. To solve the problem of computational complexity in multilevel inverters due to the large number of space vectors and redundant switching states, a simple and general space vector PWM algorithm is proposed. Based on this algorithm, the location of the reference voltage vector can be easily determined and the calculation of dwell times becomes very simple. It is also mentioned that this method requires lower memory spaces as there is no need of any look-up table. To verify the algorithms, a seven-level cascaded H-bridge inverter drive system was constructed and simulation results are present here.