Simulation Research On Modeling And Energy Coordinated Control Of DC Microgrid

In order to solve the limits of distributed generation(DG)capacity and cost as well as the difficulty of control,microgrid is proposed and it is integrated by DG,storage equipments and controllable loads.Currently,microgrid main adopts AC microgrid form,but DC microgrid has been developed rapidly because of its advantages such as low cost,high efficiency,high reliability and controllability and large capacity of power supply.This paper researches the modeling,the stability and energy coordinated control of DC microgird.At the first,this paper introduces the tolopogy structure of DC microgrid and analyzes the work principle and control strategies of every component unit.In order to maximize the use of renewable energy,PV and wind generation units operates on maximum power point tracking(MPPT)mode.PV generation unit adopts the duty-ratio perturbation and observation method combined constant algorithm and direct-driver PMSM generation unit uses the best tip speed ratio method to trace the maximum power point(MPP).Battery storage unit employs two stage charging and constant voltage discharging control to maintain the DC microgrid power balance.Secondly,this paper mainly analyzes the bidirectional operation performance of gird-connected converter(GCC)and designs and optimizes the parameters of bidirectional LCL filter.This paper designs the grid-side LCL filter parameters of neutral point clamped(NPC)three-level rectifier and inverter,and then the parameter ranges of LCL filter of bidirectional NPC three-level converter can be obtained.In order to improve the bidirectional operation performance,bidirectional LCL filter parameters can be optimized by total harmonic distortion(THD)of grid-current,setting time and stability margin.Thirdly,interface converters of DC microgrid can be devided into bus voltage controlled converter(BVCC)and bus current controlled converter(BCCC)according to the control strategy of these converters.The small signal model of each interface converter can be built and then the impedance of each interface converter can be calculated.Due to general impedance criterion,the loop gain Tm(s)can be obtained and can use Nyquist criterion to analyze the stability of DC microgrid on different operation modes.This paper builds wind-solar complementary DC microgrid simulation model in Matlab/Simulink simulation form and verifies the correctness of stability analysis by simulation experiments.At last,this paper analyzes the operation characteristics of DC microgrid and proposes energy coordinated control strategy based on dc-bus voltage.Grid-connected converter is as voltage node and controls the dc-bus voltage and power flow when DC microgird operates on grid-connected mode.The dc-bus voltage control strategy is decided by the variation of dc-bus voltage and charge of state(SOC)of acid-lead battery when DC microgrid operates on standalone mode.