Photovoltaic Power Generation System Based On Micro Grid Control Strategy Research

The operation of distributed generation access network is the trend of the development of new energy sources.But at the same time, it will have a serious impact on the operation of large power grid. Using the micro-grid way to access large power grids,both parallel operation can not only solve the drawbacks of distributed generation access,.But also give full play to the advantages of distributed generation. As a kind of clean energy, photovoltaic power generation is an ideal power source for distributed generation.This paper introduces the structure and working principle of photovoltaic power generation system and micro grid. The paper focuses on analysising PQ control, V/f control,droop control and droop control in detail. For parallel operation and islanding, these methods can be well controlled,but they can not solve the problem of microgrid smooth transition between off-grid and grid-connected.Photovoltaic inverter is the core of photovoltaic system. The photovoltaic inverter unit are detailed analyzed, a perfect photovoltaic inverter system is designed, and the simulation model is established, which meets the requirements of the design in this paper.in order to realize the problem of microgrid seamless switching between off-grid and grid-connected. When running in the grid, the inverter uses PQ control, in the switching time, the intelligent switch is switched on in time, and the inverter is controlled by V/f. From the off-grid to reconnection process is the focus of the study, if the micro direct electrical access to the large grid will because the voltage, frequency and phase synchronization and current problems and influence the power quality, and damage to electrical equipment, this paper makes an emphasis on the analysis for these problems,the micro grid and the large power grid phase always has a zero point or phase difference is very small, this moment of voltage offset and frequency offset in the allowable range. If the microgrid access the power grid wil have little effect on power quality or even no effect at this time. This paper uses PLL technology to reduce the phase difference between the microgrid and large power grid, through the detection circuit to detect phase zero crossing time, Once detecting meet the requirements of the grid-connected, closing grid-connected switches in time, inverter switching from V/ f control to control PQ.The simulation results show:under the control strategy, voltage and frequency offset are in the allowable range, can maintain the normal operation, can achieve the smooth transition of the transition process.