Voltage Control of a Three Level Boost Converter and NPC Inverter for High Power Energy Conversion Systems

In this paper, a new medium voltage power converter topology using a diode rectifier, three-level boost converter and neutral-point-clamped (NPC) inverter is proposed for a high-power permanent magnet synchronous generator-based wind energy conversion system. A significant improvement in the grid power quality is accomplished as the NPC inverter no longer controls the dc-link neutral point voltage. A model control strategy is proposed to control the complete system where the discrete-time models of the proposed power electronic converters are used to predict the future behavior of control variables. These predictions are evaluated using two independent cost functions, and the switching states which minimize these cost functions are selected and applied to the generator- and grid-side converters directly. In order to comply with the high-power application, the switching frequencies of the BOOST converter and NPC inverter are minimized and maintained below 1.5 and 1 kHz, respectively.