Unbalanced Voltage Suppression Control Strategy Of Brushless Doubly-Fed Machine For Standalone Ship Shaft Power Generation Systems

The brushless doubly-fed machine(BDFM)has no brushes and slip rings,which result in low maintenance cost,high reliability,long service life and so on.It has great potential in the field of variable-speed constant-frequency constant-voltage power generation.The ship-shaft power generation system is also one of the applications of BDFM.In this paper,an improved control strategy is proposed to suppress the unbalanced output voltage caused by unbalanced load in BDFM-based ship-shaft stand-alone power generation system.The conventional unbalanced voltage suppression control methods employ the phase angle of the positive-sequence voltage of the power winding to establish a dq synchronous reference frame for the control of negative-sequence PW voltage.However,the phase angle of the negative-sequence voltage is different from that of positive-sequence voltage,because there exists an error between the two angles,which depends on the loads.By detecting the phase error,the new method can eliminate the impact of the different types of unbalanced loads.The main works of this paper include the following aspects:Firstly,in this paper,the development and research status of BDFM are introduced,the unified reference frame dq model of BDFM is given,the relationship between control winding current and power winding voltage is derived and the control principle of BDFM power winding voltage is explained.Secondly,the basic control method of BDFM stand-alone power generation system is introduced,the influence of unbalanced load is analyzed,and the idea of unbalanced voltage suppression control is given.On this basis,the positive and negative sequence voltage decomposition and phase-locked loop structure are presented,and the negative sequence voltage elimination control equation is deduced in details.Thirdly,when the BDFM stand-alone power generation system supplies unbalanced loads and the unbalanced voltage suppression control strategy is adopted,the control winding current reference value will include the AC components.It is difficult for PI controllers to obtain zero steady-state errors when the inputs are ac components.So,the control performance of the model prediction current control and the proportional-integral-resonant control are studied respectively in this paper.The simulation model of BDFM stand-alone power generation system is built in Simulink,and the two current control methods were simulated and analyzed.Finally,based on the experimental platform of 30 KW BDFM stand-alone power generation system,the control method proposed in this paper is verified by experiments under the three different types of unbalanced load.