Research On Control Of Stand-Alone Marine Doubly Fed Shaft Generator

The doubly-fed shaft generator(DFSG)is an important component of marine electric power system.By applying DFSG,the redundant power of main engine is sufficiently used,which will help to improve the fuel efficiency obviously.Moreover,the DFSG is characterized by lower converter cost and wider speed range.When DFSG is applied to supply power for stand-alone load,its performance is influenced by marine electric load easily.The amplitude of stator voltage comes to be fluctuation,unbalance and harmonic distortion.The power quality and stability of generation system is reduced.Moreover,with the application of marine DC power system,the DC power generation operation of DFSG draws more and more attentions.Hence,by taking stand-alone DFSG generation system as the object of study,the control under balanced load,unbalanced load,nonlinear load for AC power generation and DC power generation states with DC-load connected are taken into consideration.The main contributions of this thesis are as follows:Firstly,considering the balanced load condition of stand-alone DFSG-based AC power system,an improved vector control method is proposed for rotor side converter.By designing an improved oriented method and an improved rotor current controller based on extended state observer(ESO)and non-singular terminal sliding mode control(NTSMC)method,the dependency on machine parameters is relaxed and the robustness against variable loads is enhanced.Then,the control performance of AC power generation is improved.Both simulation and experiment results are given to validate the constant voltage generating ability and variable speed constant frequency performance of designed controller for DFSG generation system.Secondly,considering the influence of unbalanced load in stand-alone DFSG-based AC power system,an improved ESO is designed to estimate the positive and negative components simultaneously.Then,an direct voltage controller based on improved ESO and NTSMC method is proposed for the regulation of rotor current converter,which can help to simplify the control structure and improve the dynamic performance.Due to the salient estimating performance of improved ESO,a specific AC signal with frequency of 100Hz is superimposed on rotor voltage to suppress negative stator voltage and keep stator voltage balance.Both simulation and experiment tests are provided to analyze the balanced voltage generating performance and verify the effectiveness of proposed controller for stand-alone DFSG system under unbalanced loads.Thirdly,considering the harmonic voltage induced by nonlinear loads in stand-alone DFSG-based AC power system,an enhanced ESO is designed for DC and sixth-frequency AC component estimation simultaneously.Combining the super-twisting sliding mode(SSM)method and enhanced ESO,an improved direct voltage regulator is proposed for rotor side converter.By injecting specific sixth-frequency component into rotor voltage,the negative fifth harmonic and positive seventh harmonic in stator voltage are suppressed.The sine degree of stator voltage is improved and the power quality is ameliorated.Then,simulation and experiment results are provided to verify the effectiveness of proposed direct voltage regulator under linear and nonlinear loads.Fourthly,by connecting the stator side of DFSG with an uncontrolled rectifier,a stand-alone DFSG-based DC power generation system is taken into consideration.To improve the dynamic performance of DC voltage regulation,an ESO-based SSM DC voltage regulator is designed.To further improve the operating performance of DFSG,the influence of harmonic currents induced by uncontrolled rectifier is analyzed.Then,a novel sinusoidal rotor current reference calculation and a resonant-ESO-based SSM rotor current controller is proposed to adjust the harmonic component of rotor current to optimum states.The designed controller can keep DC voltage constant,and suppress harmonics in stator and rotor currents simultaneously.With reduced harmonic currents,the sixth-order torque ripples of DFSG and switching losses of converter are reduced.Finally,some simulation and experiment results are provided to verify the feasibility and effectiveness of proposed controller in stand-alone DFSG-based DC power generation system.