Research On Pv Inverter Control Under Unbalanced Power Grid And Islanding Detection

The development of green energy has become an important issue as the world transform rapidly from industrial society to an environment protective society. Photovoltaic power generation gradually gets the wide concern and substantial support from the Governments because of its renewable, non-polluting characteristics. The development of the PV inverter is a solid technical foundation for the building of large-capacity photovoltaic power stations which will be a trend in the future.Based on single-stage three-phase PV inverter grid-connected system,this paper conducts the detailed analysis and research on control strategies under unbalance grid voltage and islanding protection.Photovoltaic array and maximum power point tracking is the most basic question in the study of photovoltaic power generation system. First the PV array simulation model was established by using its output characteristics. Then analyzing several common MPPT control method and selecting incremental conductance method for single-stage inverter structure to achieve maximum power tracking control.As the main part of PV grid-connected power generation system, studying the control strategy of the inverter has important significance.Assuming the grid voltage balance, in order to achieve the puipose of that the magnitude and phase of the inverter output current can be controlled,the paper use dual closed-loop control structure with the current feedforward compensation, which effectively improve the the dynamic response of the entire control system to the changes of light intensity and solve the DC bus voltage oscillation when photovoltaic array in the unstable region.In order to eliminate the second harmonic of the DC side and realize static error free tracking control of AC signal under unbalance power grid conditions. The unbalance control strategy of suppressing negative sequence of AC side and second harmonic of DC side were researched, but the system structure is complex and the positive and negative sequence current need independent testing.So an improved control strategy based on the generalized integrator under α-β coordinate system was proposed,the control method simplifies the the unbalanced control system design.Carrying out a detailed simulation study on the three control strategies, simulation results show that the improved control methods can achieve a similar effect with the traditional control methods.The inverter and the load form an island when the grid is disconnected. Island effect is a common phenomenon in the distributed power generation system, the quick and accurate island detetion has become a necessary feature of photovoltaic grid-connected inverter.This article describes the basic principles and testing standards of the islanding detection, briefly analyze and comparise several commonly used active and passive islanding detection method.Adopted a traditional reactive and active current disturbance for single-stage three-phase grid structure,which can detect the islanding quickly but the injection of current affect power quality.Then the frequency feedback reactive perturbation method was proposed, which can obtain a continuous frequency change and eliminate the effect on the power quality by using traditional disturbance. The comparision of simulation results validated the two islanding detection effect.