Z-source current-type inverters: digital modulation and logic implementation

Traditionally, current source (CS) inverters have been adopted for use in medium and high power industry applications. These inverters however support only current-buck dc-ac power conversion and need a relatively complex modulator, as compared to conventional voltage source (VS) inverters. To address these limitations, this paper presents an integration of the buck-boost Z-source power conversion concept to the CS inverter topology to develop single and three-phase Z-source CS inverters. For their efficient control, the paper starts by evaluating different carrier-based reference formulations to identify different inverter state placement possibilities. The paper then proceeds to design appropriate "reference-to-switch" assignments or logic equations for mapping out the correct CS gating signals, allowing a simple carrier-based modulator to control a Z-source CS inverter with complications such as commutation difficulties and "many-to-many" state assignments readily resolved. The developed system can be implemented using a digital signal processor with an embedded pulse-width modulator and an external programmable logic device, hence offering a competitive solution for medium power single and three-phase buck-boost power conversion. Theory, simulation and experimental results are presented in the paper.