A three-phase load is powered by an SPWM driven inverter having a single shunt-topology. During operation, drain-to-source resistances of transistors of each branch of the inverter are determined. Interpolation is performed on assumed drain-to-source resistances of the transistors for different temperatures to produce a non-linear model of drain-to-source resistance to temperature for the transistors, and the drain-to-source resistances determined during operation and the non-linear model are used to estimate temperature values of the transistors. Driving of the inverter can be adjusted so that conductivity of each branch is set so that power delivered by that branch is as high as possible without exceeding an allowed drain current threshold representing a threshold junction temperature. In addition, driving of the inverter can be ceased if the temperature of a transistor exceeds the threshold temperature.