Energy-flow direction control of grid-connected IGBT inverters for wind energy extraction

This paper presents a new inverter structure to realize energy-flow direction control in small wind turbine grid-connected inverter systems using insulated-gate bipolar transistors (IGBTs). An adequate DC link voltage is usually an imperative condition for an existing normal inverter to extract and convert wind energy to the grid. Realization of this condition is either related to the requirement of sufficient winds, or related to a complicated and expensive voltage boost scheme assembled in the generator, the rectifier, the DC link or the inverter output. However, the proposed inverter structure, at a very modest expense increase, can confine a unique energy flow direction no matter what the wind speed, the generator voltage or the inverter DC link voltage is. Based on a typical Eastern Canada wind pattern, the proposed inverter structure can extract and convert 7 to 20% more wind energy to the grid annually compared to the extraction and conversion capability of the conventional inverter structure. This paper presents the proposed inverter structure and demonstrates the results based on theoretical analysis, computer simulation and tests