Research On Photovoltaic Grid-Connected System Based On Multi-Peak MPPT

Along with the increasing of the energy and environment crisis, renewable solar energy is becoming more and more important. Solar photovoltaic connected-grid generation is the main way of solar utilization. So far, ones have made extensive research on the photovoltaic grid system, but there are still many problems not to be solved. Therefore, it is of very important practical significance to study photovoltaic grid system. A thorough study of photovoltaic grid system under shading condition is made, with emphasis on the photovoltaic maximum power point tracking, the topology structure and control stragedy and the design of the hardware and software of the system. The main research work is as follows:1. A deep analysis of the characteristics of multipeak MPPT algorithm available is made, and a mathematical model for PV array under shading condition is established. The output characteristics has been obtained by the model.A multiple peak MPPT algorithm based on the gradient method and P&O algorithm is proposed by studying the output characteristics, and the implemention of the algorithm is given and the simulation experiment is done.2. A in-depth analysis of the topology of common grid inverters and the features of their control stragedies and the output characteristics of PV array under shading condition is performed, and a determination of the two stage topology of "Boost converter+full bridge inverter" and the control stragedy of double closed loop PI is made. A simulation of the overall system is carried out by MATLAB, and the results verify the feasibility of the control stragedy.3. The hardware and software design of connected-grid system are completed. Hardware design includes the design of the Boost circuit, three-phase inverter circuit, DSP control circuit, power circuit, voltage sampling circuit, zero-cross comparitor circuit, isolated clipper circuit. Software mainly includes the system main program, MPPT control program, initialization program, lock phase control subroutine, interrupt subroutine, ADC control subroutine and sine wave pulse width modulation control subroutine.4. A3kW experiment platform is constructed. The experiments are carried out in the two cases with and without shading, and the output waveforms of the controller and the grid inverter are tested. The experimental results show that by the algorithm, the system can rapidly track the maximum power point of photovoltaic cells; lock phase control of AC current meeting grid requirement, effectively keep busbar voltage stable, and has strong anti-interference ability to the mutation of the environment...