A Maximum Power Point Tracking Technique For Partially Shaded Photovoltaic Systems And Control Method Of Micro-grid

Photovoltaic power system will become one of the most important means toobtain energy in twenty-first Century. However, two major challenges in using aPV source are the maximum power point tracking (MPPT) technics and its c-ontrol strategy.The new controller improves the hill-climbing search method by fuzzifyin-g the rules of such techniques and eliminates their drawbacks. It was the base-ment of this dissertation to establish an accurate mathemat-ical expression and its simulation of a PV array.At first, this paper deduced the equations to model aPV cell and its engineering model; In order to understand and predict the PV ch-aracteristics in a specific environment, this dissertation summarized the basic principles of forming PV array and established PV array model based on Matlab/Si-mulink. Fuzzy-logic-based hill climbing offers fast and accurate converging to t-he maximum operating point during steady-state and varying weather conditionscompared to conventional hill climbing. Simulation and experimentation resultsare provided to demonstrate the validity of the proposed fuzzy-logic-based co-ntroller.Secondly,in order to improve the efficiency of PV arrays, it is very import-ant to considering the influence of partially shaded conditions and configurations on the maximum power point distribution. In this dissertation, the equivalentPV cell model withing bypass diode had been creatived and presented MAT-LAB based modeling and simulation scheme suitable for studying the I-V andPV characteristics of PV array under a non-uniform insolation due to partiallyshaded conditions. The effects of the bypass diode,different configurations andshaded conditions patterns were focused on.This dissertation summaried the s-cope of the traditional MPPT and analyzed its cause.It can also be used for d-eveloping and evaluating new maximum power point tracking techniques, espec-ially for partially shaded conditions.Thirdly,In order to improve the utilization of photovoltaic system,due to t-he presence of multiple peaks,it combined an improved global maximum powerpoint tracking (GMPPT) algorithms. The GMPPT employed the voltage step sea-rch algorithms. Compared with global MPPT (GMPPT) search algorithm,the pre- sented algorithms lodged in this dissertation can improve efficiency. What’s more,the operating voltage range, voltage steps and the scope of the traditionalMPPT were also carefully according to the voltage fluctuation and power loss per-spective. This dissertation presented a structural framework and key techniques indevelopment of a simulation environment for the presented GMPPT algorithms.The simulation proved that the the presented GMPPT algorithm increases the s-canning time significantly and can track GPs in all shaded conditions conditions.At last, Fuzzy PID P-f/Q-V Droop Controllers for Islanded Micro-grids isproposed,which tracks MPP changes rapidly without disturbing photovoltaic sys-tem.A simulation environment for the micro-grid operation control based on twotypical control strategies which considering as P-Q,and Droop were established.The research of control laws, control structure and the choice of model paramet-ers were discussed. The micro-grid operation characteristics in the switching ofoperation modes,load changes and power changes had been studied. The dynami-c characteristic of DG and its validity had been analyzed in detail by a relevantexample. While the output power oscillates seriously around MPP. PID contr-ol is thus introduced to reduce output power oscillation and energy loss. Simu-lation results show that，the proposed method tracks MPP exactly and quickly，greatly improving energy conversion efficiency.