| With the increasingly severe problems of energy shortage and environmental pollution,photovoltaic power generation has become the most representative new energy power generation technology.The application of power electronic devices causes a large number of non-linear loads to be put into the power grid,thus generating a large amount of reactive and harmonic currents,which has a serious impact on the power quality of the power grid.Although the installation of power electronic compensation devices can solve the problem of power quality,the additional equipment makes operation and subsequent maintenance costs higher and loses economic efficiency.The photovoltaic grid-connected system with comprehensive optimization of power quality can reduce additional compensation equipment while managing on-site,which is economical and has broad development prospects.This thesis uses the equivalent circuit diagram of the photovoltaic cell to derive its mathematical model,and analyzes the output characteristic curve of the photovoltaic cell.Based on several traditional maximum power point tracking（MPPT）methods,an improved conductance increment method is proposed;the overall plan of photovoltaic grid-connected system with comprehensive optimization of power quality is constructed,and two coordinates are derived.Based on the mathematical model of the department,the system LCL filter is designed.The ip-iq method of instantaneous reactive power theory is used to detect harmonics and reactive currents.Based on this,a composite command current signal synthesis scheme is designed,and quasi-proportional resonance control（QPR）and quasiproportional complex integral control（QPCI）are studied.The comparative analysis shows that QPCI control can eliminate steady-state errors and improve the stability of the system.In view of the limited remaining capacity of the inverter and the inability to fully compensate the harmonics and reactive currents,the analytic hierarchy process is introduced to establish a comprehensive evaluation model of power quality,to study the optimal compensation control strategy under different control objectives,and to comprehensively optimize the point of common coupling（PCC）.A simulation model of photovoltaic grid-connected system with comprehensive optimization of power quality was constructed to verify the dynamic performance of the improved conductance increment method;PI,QPR and QPCI control strategies were simulated,and the results showed that QPCI control can suppress harmonics and compensate reactive power;the simulation verification of the optimal compensation control strategy under the two control objectives.The results showed that the system has the dual functions of photovoltaic grid-connected and comprehensive optimization of power quality.The related hardware circuits and software parts are designed,the overall experiment platform is built,the power quality optimization effect is analyzed,and the correctness and feasibility of the design scheme are verified. |
