Virtual Temperature Detection of Semiconductors in a Megawatt Field Converter

A converter monitoring unit (CMU) that monitors the power modules of the converter in a multimegawatt test wind turbine is presented in this paper. A method of calculating the virtual temperature (T_{v}) of the power semiconductors is laid out. Contrary to previous work, the method enables T_{v} characterization of the semiconductors by means of sampled data during normal operation of the converter, without the need for special calibration routines. The dynamic operation of the wind turbine and the large amount of data sampled in the CMU enables a statistical approach to generate reference data for T_{v} calculations. The method was tested on machine side converter diodes of the test turbine, based on samples of collector-emitter voltage (vce_{\text{on}}) and current (i_{c}). Other temperature sensitive electrical parameters may also be used as input to the method. The CMU has been operating for more than a year in the test turbine, showing consistent data throughout the whole period. While the monitoring method and results are based on measurements on a single test turbine, the paper also link these to converter failure data from a large fleet of operating turbines.