Control strategy assessment for wind turbine converter reliability

Converter reliability has a high impact on wind turbine reliability and therefore cost of wind energy. The wind turbine industry is adopting two control strategies for power converters, Direct Torque Control (DTC) and Field Oriented Control (FOC). Both control methods show high performance in megawatt-scale, variable speed wind turbines. They have similarities and differences in their way of operating and controlling the power converter. This paper investigates whether or not differences between DTC and FOC are impacting wind turbine power converter reliability. It assesses and compares converter reliability between two identical wind turbine systems, one with DTC and the other with FOC. The comparison is based on simulating a range of constant wind speeds on two wind turbine models and analysing the converter lifetime of each based on the semiconductors' thermal cycling. The results show how the operation of each control strategy affects converter reliability with the interaction of varying wind speeds. The modelled wind turbine converter IGBT lifetime drops by 26% and diode lifetime drops by 15%when the converter is controlled with DTC rather than FOC at the rated wind speed.