DSP Control of Current Sourcing Inverters

Grid connected inverters are important building blocks in renewable energy conversion systems. In conventional voltage sourcing grid connected inverters, any mismatch between the synthesized output waveforms of the inverters and the grid voltage will generate large erroneous currents unless a fast current feedback is used. The current control requires rather fast sampling rates and considerable DSP resources as well as independent hardware for protection. An alternative approach to the voltage sourcing design is to apply an inverter with an Output Current Sourcing (OCS) behaviour. Current sourcing at the output implies that, ideally, the injected current will be independent on the load voltage. This study describes a DSP control of a soft switched OCS grid connected inverter that applies a high frequency isolation transformer and does not include a costly resonant capacitor. All the required control and housekeeping functions are implemented on a TMS320F2808 DSP core of Texas Instruments. The proposed topology and possible control approaches were tested on a 3.5kW prototype. The experimental results show that the proposed DSP controlled inverter acts as a stable current source and attests to the powerful capabilities of the TI TMS320F2808 in switch mode power conversion systems.