Research On Distributed Power Grid Modeling And Control Strategy

Distributed power generation systems (DPGSs) have attracted wild attention as a clean, economical and flexible new power generation. Due to the increasing number of interconnected DPGSs, the structure of traditional power system is changing and power quality, system stability, islanding protection, Low voltage ride through are issued. As a consequence, grid-connected DPGSs have challenged traditional power system control and management. This paper made a study on the structure and control strategy of grid-connected DPGS and built accurate and reliable simulation model of grid-connected DPGS by MATLAB/Simulink.This paper firstly analyzes the structure of DPGS and gives a simplified DPGS structure as the system framework of the simulation model by a comparison between PV systems and WT systems. Simultaneously, this paper gives design goals for the simulation model based on grid requirements for DPGS.Distributed generation is connected to the grid through the filter, grid synchronization is achieved by phase-locked loop and control of DPGS is implemented by controlling the grid-connected inverter. This paper describes principle and design foundation of LCL filter and Phase-locked Loop (PLL), analyses the synchronous reference frame PLL (SRF-PLL). Because of the abnormal working of SRF-PLL under unbalanced grid conditions, the decoupled double synchronous reference frame PLL (DDSRF-PLL) is given. Based on double synchronous reference, dual vector and double loop current controller is introduced and two different methods are described to achieve LVRT.Based on the theoretical analysis, a grid-connected DPGS simulation model is built by MATLAB/simlink. The result of simulation under balanced and unbalance grid indicate that:PQ control is possible, harmonic components of output current meet the requirement and LVRT is achieved, this simulation model could be used to study on DPGS.