Static Characteristics of Split Hybrid Excitation Machine with Parallel Magnetic Path

Electrical machine is the key component of power conversion systems where permanent magnet (PM) machine is popular due to its high efficiency and high power density. However, the airgap field of the PM machine could not be regulated and then it is not qualified in some applications, such as wide variable speed operation with high efficiency in whole speed range. According to the limitation of flux regulation for the PM machine, hybrid excited electrical machines are put forward and studied by many researches in recent decades, which combine both advantages of the PM machines and electrical excitation machines [1]–[4]. There are mainly two different hybrid excitation machines according to the relationship of PM and electrical excitation path, namely serial and parallel magnetic path. In the serial magnetic path, the PM is located and serial connected with the electrical magnetic circuit which has larger resistance of the magnetic circuit due to the PM has similar magnetic permanence as the air space, and then large excitation force is needed for flux regulation of the airgap field. An effective way to decrease the excitation force of the hybrid electrical winding, is adoption of parallel magnetic path, where the PM and electrical excitation in the magnetic circuit is paralleled. However, additional airgap has to be adopted in the hybrid excitation machine to avoid short-circuit of the PM flux. The introduction of additional airgap will lead to larger magnetic resistance for the electrical excitation and leakage flux of PM going through.