Research On Hybrid Storage System And Its Control Strategy In DC Microgrids

For some remote areas with varied topography which are hard to be connected to large power grids,it is a feasible and economic proposal to use standalone DC microgrid with distributed generations to supply electric power.Photovoltaic generation and wind power generation which are mature distributed generations are of strong intermittence and wave character,which are harmful to the operation of microgrid.While they are timely complementary also,so combining these two generation systems can make up for their intermittence and wave character.If only use these two kinds of generations will cause a large need for accumulator battery,so using fuel cells can immensely reduce the cost of storage system.To reduce the cost and improve the system stability,use the topological structure of accumulator battery parallel with the DC bus through DC/DC convertor,and supercapacitor parallel with the DC bus directly,and use multi-hysteresis control strategy.To solve the problem that under some circumstances the bus voltage can deviate from nominal value a lot continuously,on the basis of traditional strategy,a voltage-level signal was defined and would be integrated to assist in switching the reference current value of the accumulator battery.Thus the accumulator battery can charge or discharge with large current when necessary even the bus voltage is not deviating from nominal value a lot.Considering that negative integral value would lengthen the switching time of reference current value when the bus voltage deviate positively,two integrator were used to assist in switching the positive and negative reference current value separately.The simulation result validated that the proposed control strategy is of advantage over original strategy on maintaining the bus voltage and improving the quality of power supply.Then wrote a genetic algorithm program aimed at the proposed control strategy.The strategy includes lots of logical judgments and can barely described by equations,so the program simulated the operation state in a whole year of the studied microgrid,to validate that the configuration can feed loads.Finally the optimal configuration has been figured out.