A comparison has been made of the power electronics lifetime for 5MW horizontaland vertical-axis wind turbines, based on dynamic models supplied with generated wind speed time series. Both two-and three-bladed stall-regulated H-rotor vertical-axis turbines were modelled, with several different control parameters. Vertical-axis turbines are likely to lead to a shorter power electronics lifetime as the aerodynamic torque varies with rotor azimuth, leading to a cyclic generator torque, and increased thermal cycling in the power electronics.An electro-thermal model of a low-voltage converter was created, and used to calculate the switching device temperatures based on the generator torque and speed time series from the turbine model. An empirical lifetime model and rainflow-counting algorithm were used to calculate the lifetime, and this was repeated at different average wind speeds to determine the overall lifetime. The vertical-axis turbine was found to have a lower power electronics lifetime than the horizontal-axis, or require a larger number of parallel switching devices to achieve the same lifetime, although this was lessened by running the turbine with a more relaxed speed control, allowing the rotor inertia to partially absorb the aerodynamic torque ripple. The three-bladed turbine was also found to give a longer power electronic lifetime than the 2-bladed, due to the lower overall torque ripple.