A Generalized Synthesis Load Modeling Considering D.C. Distributed Generation Source

Power system load model is the basis of the power system simulation. Becausethe power system load component devices have the characteristics of complexity, timevariability, diversity, and highly nonlinear, load modeling of the actual power systemis very difficult. When the distributed generation system connected into thedistribution network, load model will change inevitably. With the increasingproportion of distributed power in grid, its impacts cannot be simply neglected. Fuelcell (FC) and photovoltaic cell (PV) are bound as typical cleaning power and will beconnected to grid. So it has important theoretical and practical significance to studythe load modeling of these DC distributed power, which need to invert to grid.Firstly, this paper have builded a simulation mathematical model of the PV powergeneration system with inverter control and filtering module, and then the low voltageride through capability of the PV power generation system was verified. Based on thetransient characteristics of the PV power generation system and R-L-C equivalentcircuit, the three order differential equation dynamic model was proposed to suit gridsimulation calculation. The validity of this model and stability of the parameters weretestified by comparison simulation modeling with different disturbance levels,Based on the establishment of typical IEEE14node distribution network, theimpact of PV power generation system on composite load characteristics, withdifferent capacity ratios, different locations, was studied. System simulation analysisshowed that the distribution network load characteristics suffered the PV powergeneration system greatly with the increasing capacity ratios. Under differentlocations, the impact of PV power generation system on the distribution network isrelevant with the location of common connection point (PCC) and size of the slip load.The more PCC nears the end of the distribution network and the smaller slip load, thegreater comprehensive load characteristics suffers. At the same time, the influence ofcapacity is apparently greater than that of location, and plays a dominant role in thefactors.After detailed accounting the structure and parameters of the synthesis loadmodel (SLM) and generalized synthesis load model (GSLM) containing distributedpower, the generalized load model with PV power generation system was presented byusing the independent model of PV power generation system aforementioned. The simulation data of different capacities and different geographical influencing factorswas used to verify the validity of the generalized load model through fitting result,average fitting error and identification parameter. Comparing the description ability ofSLM and GSLM, the comprehensive performance of GSLM is superior to SLM, andcan be used to describe the characteristics of distribution network load with PV powergeneration system.Take solid oxide fuel cell (SOFC) for example, this paper studied the influencesof fuel cell (FC) generation system on the impact of distribution network. EmployingMatlab/simulation, a typical distribution network containing SOFC was builted.Through a series of transient simulation and analysis of dynamic characteristics of FCgeneration system, FC generation system can be described as second-order differentialstate equations, and be equivalent to a generalized dynamic load which consumesnegative power. Then the synthetic load model of distribution network with FCgeneration system was proposed. Such model is represented by the generalizedcomposite load model of induction motor in parallel with FC and static load. Thevalidity, ability of interpolation and extrapolation, and stability of parameters of theproposed generalized composite load model are testified better than SLM by theanalysis of simulation modeling of three typical operation states with differentinterference intensities.