The Research For Photovoltaic Grid-connected System Based On DSP

With the exhausting of the fossil energy and the increasingly serious environmental problems, all countries in the world are making an effort to find and develop new energy. Solar energy resource as a wide distribution, limitless reserves of green renewable energy has been becoming the focus of the study. Since the photovoltaic cell was developed in1954at Bell Laboratories, grid-tied and off-grid photovoltaic (PV) technologies have been updated increasingly. Especially the development of PV grid technology put more and more photovoltaic equipments into operation. Photovoltaic panel cost is relatively high at present, which requires us to understand and study PV systems furtherly, so as to obtain better stability, reliability, and reduce costs as much as possible.At first, the thesis makes a comparison among the existing grid inverter structures, and chooses two-stage single-phase grid inverter as the object of study. The principle and structure components of two-stage system are analyzed. Based on the principle analysis, developing the dedicated algorithm is discussed, including the analysis of the maximum power output of photovoltaic panel, grid current and phase synchronization analysis, as well as the energy storage capacitor voltage stability analysis. After determination of the algorithm, the design scheme of the system is decided.This thesis introduces the design of a1kW single-phase grid prototype, including hardware design and software design.In hardware design, the selection of the BOOST circuit components and parameter calculation of the circuit, and the selection of energy storage capacitor are presented. IPM PS21865is chosen as the main power switch of the inverter, of which the peripheral circuits and their parameters are designed and selected.In addition, the design of sampling circuits, protection circuits, and capture circuits are given. The adopted DSP chip is chosen to be a TMS320F2812.In software design, to control the booster and inverter circuit, the utilization of general EVA and EVB timer and full compare unit to generate PWM wave satisfying the requirement of system is discussed. Then the algorithm implementation is described.The simulation of whole system with two-stage was conducted in PSIM environment, including the MPPT control, the control of capacitor voltage of dc link, and the phase synchronization of inverter current and grid voltage. Simulation results are satisfied. Based on the complete simulation algorithm verification, a prototype with power rating of1kW was designed and implemented, and the performance has been tested. The experimental results show that the system design meets the requirements.