Reliable Power Electronics for Wind Turbines

Power electronics are used in wind turbines to convert variable voltages and frequencies produced by the generator to fixed voltages and frequencies compliant with an electrical grid with minimal losses. The power electronic system is based on a series of three-phase pulse width modulated (PWM) power modules consisting of insulated-gate bipolar transistor (IGBT) power switches and associated diodes that are soldered to a ceramic substrate and interconnected with wirebonds. Power electronics can generate thermal loads in the hundreds of watts/cm2, therefore the design of the packaging and cooling of the electronics is crucial for enhancing their energy efficiency and reliability. Without adequate heat removal, the increase in device temperature will reduce the efficiency of power electronic devices, leading to thermal runaway and eventual failure of the entire power electronic system. Furthermore, the increased temperatures can lead to failure of the packaging elements. Turbines utilizing these power electronics are often placed in harsh and inaccessible offshore environments; power electronic failures causing unscheduled maintenance lead to costly repairs. This paper will provide an overview of the fundamental package level mechanisms that can cause failures in the power electronic system. These include wirebond and lead fatigue, die attach fatigue, substrate cracking, and lead micro-voids. Attention will then be given to the reliability of a plastic-insert liquid cold plate used to manage the thermal loads from the power electronics.