A generalised hybrid multilevel modulation technique developed in case of non-integer ratio among the dc-link voltages

This paper proposes a new multilevel modulation technique designed to work with different dc-link voltage levels for each of the inverter employed in a cascade structure. This modulation technique belongs to the family of hybrid modulation techniques but it does not require that the dc-link voltage levels are in an integer ratio among them. Hence it is suited for both distributed generated multilevel converters fed by different renewable sources and UPFC, employing multilevel converters, where the regulation of the dc voltage levels can be used to meet different design requirements. Moreover the proposed generalized hybrid multilevel technique obtains optimal harmonic cancellation in respect to the carrier shifting technique that fails to eliminate some side-band harmonics due to the different dc-voltage levels. In this paper the new modulation technique is described, being compared with the traditional hybrid modulation technique, that in case of non-integer relation among the dc-links voltage levels fails in obtaining a proper first harmonic value, and with the carrier shifting technique that results in an higher harmonic content.