Study On Low Carrier Ratio Control For High Speed Dual-Three-Phase PMSG PWM Rectifier System

Traditional high speed three-phase permanent magnet synchronous generators?PMSG?have high fundamental frequency,meanwhile the power electronic devices of PWM rectifier have limited switching frequency.Thus the carrier ratio,i.e.,the ratio of the switching frequency to the fundamental frequency,of the generator-rectifier system is low,which causes problems such as distortion of the airgap flux linkage vector trajectory,increased loss and instability of DC bus voltage.From the perspective of increasing the number of motor phases,so as to achieve more voltage vectors,vector control and pulse width modulation?PWM?of the dual-three-phase permanent magnet synchronous generator?DTP-PMSG?under low carrier ratio condition are studied,providing a simple and practical way for optimizing the power generation system running under the low carrier ratio condition.Here,the traditional three-phase PMSG is denoted as single-three-phase?STP?PMSG.In this thesis,mathematical models of the DTP-PMSG are established based on different reference frames,which are the dual rotating-dq-coordinate partially-decoupled model,and the vector space fully-decoupled model.The former reveals the relation between the STP-PMSG and the DTP-PMSG,so as to apply mature models and control theory of the STP-PMSG to the DTP-PMSG.The latter,from the perspective of energy convertion,transfers the variables of DTP-PMSG into three different sub-planes,which is easy to decouple in control and clearly explain the effect of the current components on the z₁-z₂sub-plane to the stator phase currents.Then,different vector control methods of the DTP-PMSG are analyzed,including the Dual STP-SVPWM,the maximum two-vector SVPWM,and the maximum four-vector SVPWM,and detailed analysis of their digital implementation is given.Simulation models of the STP-PMSG and DTP-PMSG PWM rectification systems are established,comparing the control performance of the AC-side phase current waveforms and harmonics,the DC bus voltage ripple,and the flux linkage vector trajectory.Results show that the flux linkage vector trajectory of DTP-PMSG has better roundness and the DC bus voltage ripple is smaller,but it cannot be guaranteed to reduce the current distortion.Meanwhile,control performances of DTP-PMSG using different PWM strategies are investigated.Finally,a test rig is built and different PWM strategies on a micro-computer is imple-mented.Feasibility of different control methods of the DTP-PMSG is verified.