Modelling and control of variable frequency multiphase multi-machine AC-DC power conversion systems

This paper presents the modelling and control of a multiphase AC-DC power conversion system. The mathematical model of a system comprising of multiple Permanent Magnet Generators (PMGs) and active rectifier systems is developed. The control objectives of DC link voltage stabilization, minimized reactive power transfer and dynamic load sharing issues are addressed. The system transient load sharing is achieved by matching the controller gain values with the load sharing requirements. Methods of steady state load sharing viz. automatic master-slave control and droop based load sharing are developed for the application of parallel PMG and rectifier systems. A droop regulation scheme for DC link voltage control is proposed. The properties of each method are discussed. Simulation results are presented for a system with five fault tolerant multiphase PMG fed active rectifier units. The system is subjected to a severe loading step demand and the DC link voltage and the load sharing characteristics are analysed.