| With the rapid development of the world’s economy and technology, the conventional energy sources are running out fast due to the larger and larger amount of energy consumptions caused by the ever increasing industrialized population. Being one kind of renewable energy, solar power becomes a critical means to solve the international problem of energy source exhaustion. Solar power is a kind of clean and costless energy with almost infinite supply. To exploit such kind of environmentally friendly energy source, researchers are investing much attention on photovoltaic generation systems (PGS), which possess the advantages of long life span, less territory restriction and strong capabilities of disaster-relief and self-salvation. As the critical component in PGS, the photovoltaic power control system (PPCS) is being extensively investigated in the aspects of efficiency, quality, reliability, capacity and function.This thesis aims at studying the key technologies in PPCS, including mathematical modeling of solar cell, designing of algorithms for maximum power point (MPP) tracking, modules of battery charge/discharge, parameter calculation of DC transform modules and invert modules, close-loop control strategy of sine wave inverter, and hardware design. Using these key technologies, we design a two-level multiple-string PPCS based on a Master/Slave control mode. Specifically, this control system is powered by a microchip of type TMS320F28035manufactured by TI in order to realize full digital control in the Master/Slave mode. The system contains a DC transform module (DCTM) and an inverter module (IM). The former’s task is to efficiently track the MPP of the multiple-string solar cells so as to maximize the power output; whereas the latter’s task is to directly generate a50Hz/220V AC voltage without AC transforming so as to improve the energy conversion efficiency. Communications between the two modules are conducted through the RS485communication bus, which makes the system more extensible and flexible for energy management.Besides the PPCS, we also construct a simulation model based on the equivalent mathematical model of solar cells with the S-function in Matlab/Simulink. Referring to the characteristics of real solar cell module, the simulation model can generate realistic characteristics curves, thus verifying its correctness. This accurate simulation model enables us to1) develop and test a new MPPT algorithm by integrating the constant-voltage method and optimal gradient method;2) derive parameter calculation method through an in-depth analysis of the relationship between the chopper boost circuit and the main components in the invert module;3) design a suitable LC filter circuit capable of providing key references of hardware components like IGBT and IPM based on the calculated parameters;and4) design the hardware circuits that constitute the whole PPCS, including the DCTM based on boost circuit, IM based on IPM and the intelligent circuit for battery charging/discharging based on UC3909. Furthermore, we select the conventional double closed-loop control strategy to control the inverter. The control accuracy of the system is ensured by optimizing the PI adjuster based on the eliminating nonsense region method. We also introduce the SPWM wave generation mechanism and choose single-polarity SPWM wave as the control wave to generate AC voltage, which will reduce the voltage harmonics of the output. Experiment results suggest that our scheme can meet the design requirement satisfactory. |
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