Key Technology Of MPPT And Grid-connected Inverter Of Photovoltaic Power Generation

As the two key technologies of renewable energy areas, Maximum Power Point Tracking (MPPT) technology and inverter grid-connected technology have become the focus for engineers. This thesis studies MPPT technology, inverter grid-connected technology, and presents some characteristics of the inverter grid-connected from control methods perspectives.The uncertainty of ambient temperature and light intensity result in nonlinear drift of maximum power point of photovoltaic cells. To solve this practical problem, photovoltaic MPPT control technology derived. Although many MPPT algorithms have achieved good results, there are still many problems in practical applications, especially the problem of turbulence near the maximum power point. Combining with traditional excellent algorithms,the thesis proposes a new MPPT algorithm to solve the problem of turbulence. The fact that the power of the photovoltaic cells is small and the power consumption of the conventional MOSFET driver is relatively big, directly restricts the verification of hardware implementation of the new algorithm. For this reason, the thesis proposes a patent-pending high-efficiency MOSFET driver.Because whether the grid-connected inverter system is stable or not will greatly affect power grid, the most important characteristic of the grid-connected system is robustness. Consequently,the classic PID control algorithm is selected as the research subject. To design the PID parameters, this thesis introduces the root frequency of second-order system in control theory instead of constantly debugging in most previous literatures.The deduction and analysis of the continuous and discrete grid-connected inverter with L and LCL filter is presented in detail and based on that, proper parameters are selected for the PID controller design. On the basis of the inverter model,the thesis derives the formulas about how to design the L and LCL filters according to unipolar SPWM modulation strategy.After the theory description, L and LCL grid-connected inverter systems are simulated, using Simulink and SimPowerSystems to build the models of controller and power circuit respectively. Since Real-Time Workshop requires the Simulink solver to be a fixed step size type, and the sampling frequency is limited by the Quanser system, the traditional SPWM modulation strategy fails. Utilizing some features of the Quanser hardware system, a SPWM modulation strategy, similar to the unipolar SPWM modulation, is proposed to solve the problem. Finally, using the feature of the seamless connection between the Quanser system and Simulink,a grid-connected electricity generation platform is realized.