Parallel hybrid excitation machines and their control schemes for DC generation system

The parallel hybrid excitation machines (PHEM), which exhibit good flux regulation capability and wide constant power operating capability, can not only reduce the coupling of the PM flux and electrical excitation flux but also avoid demagnetisation that occurs in the series hybrid excitation machines. This study compares and analyses the electromagnetic performance of different PHEMs with emphasis on the excitation source location, structures, operation principles, reliability and axial utilisation. Then, their control schemes for voltage regulation of DC generation systems are analysed based on different critical control variables including the excitation current, the armature current, the electromagnetic torque and the applications are also discussed. Furthermore, an improved direct torque control (DTC) scheme is investigated to improve the system performance. A parallel hybrid excitation flux-switching generator employing the improved DTC, which shows excellent dynamic and steady-state performance has been achieved experimentally.