Control Of Wave Power Generation Arrays With Modular Multilevel Converter

Ocean energy is an important renewable energy. Our country is a great ocean state so that we can abundantly take advantage of the wave energy. The energy density of wave motion in ocean is very high and the ideal electrical energy production time of the wave energy converter(WEC) can be as high as 90%.Although research of wave energy power generation starts late compared to other renewable energy power generation such as wind power and solar power, it has a crucial role for the long-term development targets for renewable energy of our country.As wave energy generation technology processes mature, the construction project of wave farms have been increased into schedule to achieve it's the commercialization and large-scale application. The study has important theoretical and practical significance as wave farms may allow considerable savings in terms of the cost of mooring, electrical connection and maintenance. Reasonable layout of wave energy device arrays can improve the capacity of the array. Meanwhile, electrical coordinated control of the wave power array is usually needed to make the wave-power farm could output maximum power steadily and smoothly.The wave energy device arrays are fully investigated in this thesis and the work is mainly as follows:(1) Research achievements of wave energy generation, principles of typical WEC and multi-degree of freedom WEC and wave power generaion arrays are introduced with the development of wave power technology at home and abroad described.(2) The influence of the spatial configuration of a wave power generation arrays upon total power output is investigated. Mathematical model of the array is presented.A hydrodynamic solution is constructed to the problem of multiple interactions amongst array units with linear wave theory. Hydrodynamic interactions are computed by MATLAB software. The array configuration is optimized by using two different approaches: the parabolic intersection method and differential evolution method.(3) In order to improve the output power quality and the adaptive expansion ability of the array system capacity, a modular multilevel converter(MMC) is used as the grid-connected inverter of the array system. The mathematical model of MMC is built in abc coordinates and dq coordinates respectively. The related pulse modulationtechnology is studied. The composition and mechanism of circulating current and sub module capacity voltage of MMC are analyzed.(4) The simulation model of a grid-connected array system is built and the corresponding grid-connected controller and dc capacity voltage balance controller are designed. The circulating current is suppressed by direct suppression and based on PR(Proportional Resonance) controller. Simulation results validate the accuracy of these proposed control methods.