Research On Power Optimization Control Of Direct-drive Wave Energy Converter

With the advantages of huge storage,high energy density,renewable and non-polluting,wave energy has been attracting the attention of the world and also highly advocated to develop its relevant power generation technology.However,due to the disorder of ocean movement and the suitability between wave and device,the current wave energy converter has low energy capture efficiency,poor operation stability,and slow progress in engineering applications.Based on the permanent magnet linear synchronous generator,this thesis takes direct-drive wave energy converter as research object,whose research interest refers to the power optimal control strategy of the system running in irregular sea area.First,in order to intuitively describe the motion of the direct-drive wave energy converter running in the wave,the hydrodynamic equation of the float is derived on the basis of potential flow theory and Newton's second law;then the mathematical model of the permanent magnet synchronous motor after coordinate transformation is established,which contributed to the mathematical modeling of the whole machine in the time domain.The state observation technology is used to monitor the state variables of the system in real time to evaluate the stability of the unit,and at the same time as the feedback of the MPPT control law,aiming to overcome low detection accuracy of the mechanical sensor under complex sea conditions.The simulation results show that the Luenberger observer,sliding mode observer and Kalman observer can all realize sensorless measurement,among them the LKF observer has fast convergence speed,strong robustness and filtering effect.For improving the energy capture performance in the irregular wave,the main frequency prediction technology are proposed to extract the main period segment from the wave spectrum,which led to transformation into a regular wave MPPT strategy to solve the resonance parameter matching problem and increase the system output power.While the noise component within the irregular wave will affect the accuracy of the conventional main frequency prediction algorithm,thereby influencing the selection of parameters in the equivalent resonant current and the effect of power optimization.Therefore,a main frequency prediction technology based on Rife method is proposed to improve such problems.The simulation results showed that the out power is obviously increased after the application of the main frequency prediction technology,among them the Rife algorithm was able to estimate more precise main frequency wave than the results of the FFT and windowed FFT algorithms,combining with the best power improvement effect.Dealing with the limitation of main frequency strategy which ignored the wave energy of secondary wave component,an energy functional subjected to the WEC under irregular wave condition was proposed to derive the MPPT optimal control law using the variational method.Following with the consideration of model mismatch caused by the structural parameter errors,the adaptive compensation technology was used to derive the equivalent compensation control law,and jointing such two control laws can control the anti-electromagnetic force which enabled the generator to output the maximum energy while compensating for the power loss created by the parameter deviation.The simulation results show that the energy captured by the proposed MPPT strategy in the irregular sea area is much higher than that of the main frequency strategy.After combining with the adaptive compensation control law,the mismatch error of the model is reduced,and the relevant power loss is compensated.