Permanent Magnet Biased Inductors–An Overview

This article provides a comprehensive overview of the state of the art in the field of permanent magnet biased inductors, (PMBIs). The theoretical benefits of PMBIs, operating in DC applications, were identified decades ago, in the late 1950’s. Compared with a non-biased inductor, a 100% linear biased PMBI, can achieve the same inductance and saturation current, while requiring only half of the core's cross-sectional area or half the number of turns. In practicality, achieving 100% biasing without introducing additional losses, or detrimental conditions for the permanent magnet's lifetime, becomes an important challenge and the development and achievements of PMBIs have been evolving until present days. Therefore, this overview paper, first introduces the basic background knowledge required for the development of PMBIs, including an overview of the design benefits of biasing, the possible design strategies, additional benefits and possibilities of over-biasing, and a brief introduction to permanent magnets, PMs. The historical evolution of the different biasing techniques, and the employed core and PM topologies, are analyzed and evaluated. The different physical prototype implementations found in the literature, and their operating characteristics, achievements, and limitations, are compiled and evaluated. Finally, the present challenges of PMBI implementation, and the future perspectives towards optimized development are summarized.