Study On The Key Technologies Of The Grid-connected Marine Current Turbine's Control System

With the 13th Five Year Plan of China Ocean Renewable Energy released,a series of goals have become clear,including to mature the ocean energy equipment technologies,to promote the ocean energy's industrialization and to change "can generate electricity" to "generate electricity steadily".Marine current energy is a kind of unending supply of ocean energy.Maine current energy equipment is the focus of the maritime strategy,the new energy research hotspot and the advanced design and manufacture.Marine current energy technology has made significant progress in the past decades.Marine current turbines(MCTs)are developing towards the megawatt power,array installation and commercial operation.It gives a higher request to control methods.Therefore,to improve the MCTs' power efficiency,operating reliability and power stability by control system and method is particularly meaningful.Hardware and software design of a 120 kW grid-connected MCT's control system is completed in this paper according to the analyses of the control system's hardware and software architecture and functional requirement.Then,both workshop test and sea trial are carried out.Based on the designed control system,power control strategy and grid-connected control strategy of the MCT are studied.Their simulations and experiments are also researched.The contents of each chapter are as follows:In Chapter 1,the research background and significance of this article are presented.The marine current's characteristic and disturbution are introduced firstly.Overviews of the research history and status of marine current energy equipment,MCT control system and technology in both the worldwide and China are then proposed.Furthermore,the existing difficulties and inadequacies of the marine current energy control technology are summed up.Finally,the main research contents are proposed based on the research significance and the source.In Chapter 2,the power characteristic and composition structure of the grid-connected MCT are introduced.The Betz' Law and blade element momentum theory are used to analyze the horizontal-axis MCT's capturing principle.In addition,parameter corrections are made to the blade element momentum theory,considering its defects.Output power characteristics are given for the marine current energy conversion system(MCECS)operation.The composition structure includes the pitch system,mechanical drive train,and grid-connected system.Meanwhile,the control system's composition structure and function topology are briefly introduced.In Chapter 3,the MCT's control system design is presented.Control target and logic,system design principle are proposed according to the operating characteristic of the MCT.Hardware and software of the 120 kW control system are designed,including hardware and software function topology,signal flow,control system's circuit,safety chain,control logic,and so on.In Chapter 4,control strategies of the grid-connected MCECS are studied.The mathematical models of the whole system are built.Pitch controls based on the direct angle feedback and the power feedback are studied respectively.Optimal speed control,optimal torque tracking control and torque vector control of the permanent magnet syschronous generator are significantly studied to achieve the maximum power capturing.In addition,a fuzzy control strategy based on the variations of the generator speed and power is proposed to improve the power efficiency and smooth speed fluctuation.Based on the dq-reference model of the grid-connected system,a double loop control method is employed to regulate the active and reactive power.Meanwhile,a software phase lock loop control method is used to track the grid voltage vector.The system dynamic characteristic and control performance are verified by simulation.It can be obtained that the horizontal-axis MCECS can run stably with a high-energy efficiency and high-quality electricity fed into the grid.In Chapter 5,experimental results of the grid-connected MCECS are discussed.Workshop tests and Sea trials of a 120 kW horizontal-axis MCECS are carried out.The reliability and stability of the designed control system,the feasibility of the pitch,power,and grid-connected controls are validated.In Chapter 6,some control strategies of the grid-connected MCECS are proposed to enhance the whole system's operating characteristic in accordance to the existing deficiency in the sea trial running.These control strategies include the pre-pitch control strategy for starting under low current velocity,the reduced variation pitch control strategy based on marine current velocity preview,and the indirect maximum power point tracking control strategy through setting an appropriate DC-bus voltage.Methods of simulation and experiment are utilized to verify the control improvement,including improving the power efficiency and system reliability,reducing damage,and prolonging system working life.In Chapter 7,the main work of this paper is summarized,and the conclusions and innovations are expounded.Besides,the future research work is prospected at the end.