Derating

In previous chapters, we discussed the converter with or without fault. The common similarity between them is that they continue to operate without reduction of their nominal specification. In this chapter, uninterrupted operation of a faulty power conversion system with catastrophic damages in some of its parts is investigated. It is shown that a faulty electric power converter can continue to work with degraded specifications. This algorithm is named derating for accessibility. This technique can be used for both a faulty system because of its uninterrupted operation and a normal system because of extensive life time. Algorithms for derating of a faulty electric machine and a power supply are described. Derating for increasing the useful life of a motor drive system is presented. A novel method for switching frequency selection in a switching power supply is proposed based on derating concept. Derating is introduced as a technique to compensate additional losses in an electric power converter operating in harsh environment (for example: a motor drive which is supplied with a non sinusoidal voltage waveform). Industrial examples are presented in details for better understanding of the derating concept. Some of the presented examples contain novel idea for derating and others are well known in industry.