A hybrid modulation method for lifetime extension of power semiconductors in wind power converters

Pulse width modulation (PWM) techniques can be classified into continuous pulse width modulation (CPWM) and discontinuous pulse width modulation (DPWM) types. The switching loss of power devices in DPWM converters is lower than that in CPWM converters. Lower loss could reduce the junction temperature fluctuation in converters of wind turbine generator system (WTGS) and may result in longer power devices lifetime. However, employing DPWM scheme under all WTGS operation conditions will lead to power quality concern. To solve this problem, a new hybrid modulation scheme which combines the CPWM and DPWM methods for WTGS converters is presented in this paper. In the presented hybrid modulation method, two modulation schemes are switched back and forth according to the wind speed in the wind farm site. The performance of the presented modulation scheme is verified and compared with that of other PWM schemes through a case study of 1.2 MW WTGS in long-term mission profiles. The results show that the lifetime of power devices with the presented hybrid approach is longer than that with the CPWM, and is shorter than that with the DPWMs. Moreover, the power quality of the power converters with the hybrid modulation scheme can be guaranteed in all operation conditions, which may not be achieved with DPWMs.