Current-source Power Conversion Technology And Its Application In HVDC System

According to the different energy storage components,power convertors are divided into two categories,voltage source convertor and current source convertor.Voltage source converter technology,based on its variety of topological structure,perfect modulation technology,and higher efficiency of energy stored in capacitors,and voltage of capacitors easily controlled,becomes mainstream in power transformation equipment.For many years,by the limit of energy storage components,current source converter technology is not further developed,such as its topology structure and modulation technology,which are relatively lagging behind.With the development of modern control theory and soft switching technology,and increasing voltage of half-controlled power components,current source converter technology shows the advantages of applying in higher voltage and high power filed.Firstly,the dissertation introduces the concept of dc ripple reinjection,and harmonic elimination principle of 6,12 pulses convertors which adopts current reinjection method.Complete convertor topology and control theory are obtained by the study of generalized current reinjection convertor.Making 12 pulse converters to be object,it verified the feasibility of harmonic elimination with reinjection current in 12 pulse converters by Fourier decomposition of current mathematical model.Error square and error derivative square reinjection method and linear reinjection method are analyzed.Simulation models of current reinjection 6,12 pulses convertor are built and verified in Matlab/Simulink.Secondly,the dissertation expounds topology structure and reinjection current control methods of MLCR-CSC.Amplitude,phase,and THD mathematical model of AC-side current is showed clearly.It also explains the magnetizing current synthetic principle,and the selection theoretical basis of main segment.Building models of SLCR-CSC in Matlab/Simulink,simulation results show the realization of harmonic elimination,zero current switching and unit power factor operation.For different levels of reinjection current,it obtains the optimal duration of zero current through analysis of mass simulation experiments data.It builds up a 1 MW physics experiment platform,and designs integrated control platform based on DSP and FPGA.Experimental results and theoretical simulation are almost same.Furthermore,the dissertation proposes double MLCR-CSCs topology in series,and discusses its application in HVDC.It adopts active power and reactive power decoupling control method,and sets up DMLCR-CSC nonlinear mathematical model.Based on affine nonlinear state feedback exact linearization theory,it gets accurate linear control model.It also shows power flow calculation method which contains DMLCR-CSC,and designs the converter fault control strategy.Simulation results show that DMLCR-CSC could control of active power and reactive power independently,reach a new equilibrium state quickly during small disturbance.Taking single-phase grounding fault on AC-side for example,it shows the fault behavior of HVDC converter containing MLCR-CSC.Meanwhile,it establishes zero current shut off condition in order to get a new balance or downtime during short circuit at DC-side.Fault recovery time is about half of that of the traditional convertor.In addition,the main studies of the dissertation are the theoretical research of MLCR-CSC harmonic elimination,current zero run off and high power factor,and setting up 1MW experiment platform.Software simulation and physical experiment test results both verify the validity and feasibility of current reinjection technology.Based on nonlinear control theory,it realizes the power decoupling control.Through Matlab/Simulink and experimental verification,current injection technology has positive significance in the design field of converter and HVDC transmission.