Distributed Wave Energy Generation Control Strategy Based On DC Microgrid

The ocean energy is a kind of renewable energy with high power density,no pollution,abundant resources,etc.The energy crisis and environmental pollution can be alleviated by utilizing ocean energy.However,wave energy utilization are low efficiency,poor quality and high cost due to the intermittent and uneven distribution of wave energy,thus,the development of wave energy generation industry is restricted.Microgrid integrates various types of distributed generation(DG),and it can reduce the adverse effects when DG access to power girds.Therefore,in this paper,the distributed wave power generation control based on DC microgrid is studied as follows.Firstly,in order to improve the overall efficiency of the wave energy collection,this paper applied a direct-drive wave energy generator to simplify the wave energy extraction process and improve the efficiency of wave energy conversion.A mathematical model is established for the wave motion and the direct-drive wave energy generator,and the output characteristics curves of the wave power generators are acquired under the sine wave motion.Based on the characteristics of wave instantaneous power,the maximum power tracking strategy of wave energy generator is studied,and the combination of an uncontrollable rectifier and boost circuit greatly simplifies the maximum power tracking control structure of the generator.Secondly,in order to smoothing the fluctuation of instantaneous power of wave energy generation,this paper proposes a power smoothing strategy based on super-capacitor(SC)as energy storage unit.The voltage control of DC microgrid is considered as three state patterns separately,to guarantee the power balance under any generator power fluctuations or load changes.Finally,the simulation results are provided to demonstrate the feasibility of the presented control strategy.Thirdly,this paper presents an advection-based coordinated control algorithm applied to power dispatch of the distributed wave power generation control with DC microgrid.Specifically,the proposed control algorithm can achieve consensus status information among the wave energy power generation nodes with unbalanced conditions,while the total charging/discharging power can be flexibly adjusted according to a power command.Finally,simulation results are presented to verify that the algorithm can effectively manage and control multiple wave energy power generation nodes power output.Lastly,the layered control strategy of distributed wave power with microgrid is introduced.The hierarchical control structure of microgrid includes primary,secondary,and tertiary levels.The problem of voltage deviation caused by primary controller is analyzed,the secondary controller is introduced to solve the problem of voltage deviation,tertiary controller in the microgrid energy control method is given.Finally,hierarchical control verified by simulation can effectively adjust the micro grid bus voltage,and energy flow with external power grid can be controlled.