7 MAGNETIC CIRCUIT CONCEPTS

The purpose of this chapter is to review some of the basic concepts associated with magnetic circuits and to develop an understanding of inductors and transformers needed in power electronics.

7.1 AMPERE-TURNS AND FLUX

Let us consider a simple magnetic structure of Figure 7.1 consisting of an N-turn coil with a current i , on a magnetic core made of iron. This coil applies upper N i ampere-turns to the core. We will assume the magnetic field intensity upper H Subscript m in the core to be uniform along the mean path length script l Subscript m . The magnetic field intensity in the air gap is denoted as upper H Subscript g . From Ampere’s law, the closed line integral of the magnetic field intensity along the mean path within the core and in the air gap is equal to the applied ampere-turns:

upper H Subscript m Baseline script l Subscript m Baseline plus upper H Subscript g Baseline script l Subscript g Baseline equals upper N i period (7.1)

FIGURE 7.1 Magnetic structure ...

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