Robust Current Control Of Parallel Inverters In Wave Power System

Ocean energy is an important renewable energy which is dependent in seawater,mainly behave as forms of waves、currents、tides and salinity difference in the ocean.Wave energy refers to the mechanical energy of waves on the ocean surface.It has the maximum current density and is widely distributed.Wave energy is the energy of the highest quality in the ocean,and can be achieved by using a small device and can emit considerable and cheap electricity.Therefore,wave power generation has obtained much attention in the coastal nations of the world in recent years,development planning in the world has confirmed that wave power project is an important development and utilization of marine energy,and is an important component of clean and non-polluting new renewable energy sources.With the development of wave power technology,designing of wave power arrays was put on the research agenda in the purpose of achieving large-scale wave power.Its advantage is saving costs of mooring system、power transmission and equipment maintenance,achieving large-scale utilization of wave energy to generate electricity.It has important theoretical and practical significance.We need to research the electrical topology of wave power arrays,the generators,energy storage,and inverter control strategy,and electric coordinated control strategy of the whole wave power arrays,so that the wave power arrays can output smooth and stable power.The electrical parts of wave power arrays system are fully investigated in this thesis and the work is mainly as follows:(1)Research achievements of wave power generation,principles of typical WEC and wave power generation arrays are introduced with the development of wave power technology at home and abroad described.(2)Electrical part of the wave power arrays obtained a detailed analysis and design.Comparative analysis for the overall design of a variety of electrical topology for wave power arrays is done,suitable electrical topology for wave power arrays is summed up.Detailed analysis of control strategies for float-permanent magnet synchronous generator are carried out,a suitable control method for the float-permanent magnet synchronous generator is summed up.Energy storage system is used to stabilize the DC bus voltage,the simulation is executed by selecting the appropriate control strategy.Parallel and grid-connected inverter technologies are discussed and analyzed,selecting the appropriate control strategies to build a model in simulation software and simulation experiments are executed.(3)A robust control strategy for the grid-connected parallel inverter system is developed.Based on the analysis of the circuit structure and circulating current of the parallel system,a method of single leg robust controlling is proposed.Structured singular value μ synthesis based on H∞impact of various uncertainties,and improve the stability and performance of the parallel system,so that the accurate current control and circulating current restraining is realized.Further,the scope of the uncertainty is given for stable operation of the system,and the controller can ensure the stability in the given range.(4)Constructing the three-phase parallel inverter system simulation models,and apply robust controller as inner current controller.The simulation results show that the robust controller applied in a three-phase system can decrease the impact of various uncertainties,and the accurate current control and circulating current restraining is realized.Indicating that the robust control method for three-phase grid-connected inverter parallel system is effective.