Research On Control Strategy Of Bidirectional PWM Rectifier In Hybrid Power Grid

The hybrid power grid can effectively convert green energy commonly found in nature into electrical energy through distributed power generation and promote large-scale use of green energy.As the core of hybrid power grid control,bidirectional converter plays an extremely important role.This thesis takes bidirectional PWM rectifier applied to LCL filtering in AC/DC hybrid power grid as the research object,and mainly solves two key problems:(1)Aiming at the complex problems of LCL filter parameter design,a design of LCL filter parameters optimization for multi-objective optimization based on a particle swarm optimization(Particle Swarm Optimization,PSO)is proposed.(2)Aiming at the problems of slow steady-state response on DC side,large steady-state fluctuations and severe harmonic distortion on AC side in traditional PI control,linear auto disturbance rejection controller is proposed(Linear Auto Disturbance Rejection Controller,LADRC)to replace the traditional PI controller to control the PWM rectifier to achieve more stable,effective and optimized control of the rectifier when the hybrid power grid is running.The specific research contents are as follows:First,the topology of the hybrid power grid is introduced,and the micro-sources used in this thesis are studied.Analyzing the operation mechanism of photovoltaic cells,establishing an equivalent model of photovoltaic cells,and using the Maximum Power Point Tracking(MPPT)to achieve effective control of photovoltaic output;designing double-loop control of energy storage batteries in grid-connected and islanded modes to achieve bidirectional DC / DC control of energy storage batteries.Secondly,the model building and control strategy of the bidirectional PWM rectifier are detailed designed,which is the focus of this study:(1)The main circuit topology of the rectifier based on LCL filtering is designed.According to the circuit theory,the mathematical model of the topology is established in a two-phase rotating coordinate system(dq)and the three-phase static coordinate system(abc),and its four-quadrant operation mechanism is analyzed from a physical point of view;(2)The cost function,loss function,and harmonic function are used as optimization sub-goals,which are linearly weighted construct a single objective function for PSO optimization,and complete the optimal design of LCL filter parameters;(3)Traditional PI control has problems such as long steady-state response time,slow dynamic response,large steady-state fluctuation,and serious harmonic distortion.Therefore,this thesis uses the LADRC controller to replace the traditional PI controller to control the bidirectional PWM rectifier of the hybrid power grid,to achieve the optimal control of the DC side voltage,current,AC side frequency,harmonics and other performance indicators.Finally,the hybrid power grid system is built on the Matlab / Simulink platform,and the simulation and analysis of the hybrid power grid on-grid,off-grid and mode switching modes are carried out.Compared with traditional PI control,LADRC control has the advantages of rapid dynamic response capability,shorter steady-state response time and smaller steady-state error,smaller harmonic distortion change,and smaller frequency fluctuation,which fully verifies the superiority and effectiveness of hybrid grid bidirectional PWM rectifier control strategy based on the LADRC which is proposed in this thesis.