Study On Maximum Power Tracking Control Of Direct-Drive Wave Energy Conversion

In order to accelerate the improvement of energy structure,protect the environment,develop a low-carbon economy,and increase the proportion of renewable energy,China is vigorously developing renewable energy,and wave energy as a clean energy with great development potential is also receiving increasing attention.The wave energy conversion system(WEC)adopting the direct-drive power takeoff technique has effectively improved the wave energy utilization efficiency,is easy to maintain and has a simple and reliable structure.It is becoming a research hotspot for wave power generation.Archimedes wave swing(AWS)as the first direct-drive WEC device has a simple structure and high efficiency.This article takes the AWS system in direct-drive WEC as the research object,modeling the system's float and linear permanent magnet generator(LPMG),maximum power tracking control,three-phase voltage source rectifier(VSR)control and energy storage unit Power smoothing control and other issues are studied.Based on the characteristics of AWS power generation system,this paper establishes mathematical models for floats,permanent magnet linear generators,three-phase voltage rectifiers,and studies the control of each part.LPMG can output maximum power when AWS resonates with waves.For wave power maximum power tracking control,different wave force conditions were studied.(1)Under the condition of regular wave force,two power tracking algorithms,amplitude control and amplitude-phase control,are designed to derive the optimal anti-electromagnetic force curve and further determine the reference current value.(2)Under the condition of irregular wave force,through the analysis of the linear system,the q-axis reference current is deduced.Using decoupling control to achieve independent control of the d-axis and q-axis currents,maximize the use of generator capacity.The PI controller parameters are designed according to a typical type II system to realize the fastness and anti-interference of current tracking.Realize the control of three-phase VSR through SVPWM control.Due to the reciprocating movement of the float,the amplitude and direction of the moving speed of the mover are all changed,resulting in changes in the output power,the terminal voltage,and the frequency of the generator.This characteristic of output power makes it unable to meet the conditions of use,and power regulation becomes important.Therefore,the role of the energy storage unit in smoothing the output power of AWS is studied.In order to smooth the output power of the generator,the output power is compensated and stored by the battery energy storage,so that the output voltage and power of generator are maintained within a certain range.Based on the above modeling,control methods and analysis,a MATLAB/SIMULINK simulation platform for AWS power generation and its control system was established to simulate the operation of the AWS system under no-load conditions,uncontrolled rectification conditions,optimal control algorithms under regular wave and irregular wave conditions,under wave force variation conditions,respectively.and the simulation results were compared and analyzed.The simulation results show that the amplitude-phase control algorithm can output more power,and the designed maximum power tracking algorithm can be applied to irregular wave forces,verifying the correctness of the established model and the effectiveness of the control methods of each subsection.