Soft-switching of a hybrid bi-directional Current Source Converter

A three-phase Hybrid Current Source Converter (HCSC) that employs 3 SCRs and 4 switches (IGBTs) was proposed as an economical alternative to the conventional 6-switches Current Source Converter (CSC). It presents bi-directional power flow capability, does not generate low order harmonics and can operate with variable power factor. However, the force-commutated switches need to operate with increased switching frequency and remain on for minimum periods of time for safe commutation of the SCRs what leads to a reduced maximum modulation index (m_amax). This paper describes a space vector modulation (SVM) technique that allows one natural (soft-switching) commutation of SCRs and IGBTs per SVM cycle. Besides, the reduced stress on the semiconductors, this allows the use of SVM sequences with three segments and an increase on the maximum modulation index (m_amax) of the 3-SCR and 4-IGBT HCSC.