Research On Direct Power Control In Three-phase Photovoltaic Grid System

Energy crisis, environmental poses a serious threat pollution to sustainable humandevelopment, use of renewable and clean energy research has become the focus of attention.The core of photovoltaic grid is the grid of AC side solar is connected to the DC side, toachieve energy transfer, so that you can supplement the energy grid, which provides to users.Stage photovoltaic grid technology, there are still major challenges as follows:1. highproduction costs of photovoltaic materials, production processes require high conditions,2.photovoltaic cells to solar radiation at the surface of its low conversion efficiency of energyavailable,3.real-time tracking the maximum power output of solar cells difficulties,4.photovoltaic and stability, a certain impact on the whole network security and reliability ofthe grid system exists. In view of the existence of the problem, this paper analyzes the3and4point and focuses on the grid control strategy.Grid-connected inverter is the combination of the new energy grid hub, harmonicpollution, low power factor, the control system complexity and poor performance-based anddynamic stage presence photovoltaic grid system. Based on the instantaneous power theory,the power grid inverter mathematical model, the direct power control (direct power control,DPC) strategy applied to the three-phase grid-connected photovoltaic systems, the analysis ofthe traditional switch tables exist for reactive power, active regulation is poor, thereinadequacies uncontrollable zones, we propose a new type of switch tables.As traditional DPC requires four sensors to provide real-time monitoring data for thecontrol strategy due to excessive use of sensors, the control system increases the cost. Forthese reasons, the AC motor stator flux reference concept, introduced the concept of virtualflux (VF), and the virtual flux with direct power combined to achieve a non-grid voltagesensor directly photovoltaic grid power control, while direct power of traditional hysteresiscontrol the switching frequency is not fixed, in order to solve this problem, the VF-DPCcontrol systems and space vector (SVM) combined to achieve the VF-DPC-SVMphotovoltaic grid. Good value for the future project development and utilization of newenergy sources.