I. Introduction
Due to the concerns about the supply and price of rare-earth permanent magnet (PM), significant efforts are focused on the development of less magnet or non-magnet machines recently. The doubly salient structure is simple and robust, which makes it very promising for automotive applications. However, to achieve high torque density and high efficiency over a wide speed range, the capability to adjust the air-gap flux density is the state of the art for the automotive applications.