Research On Stability Control Of Coal Bed Gas Field Hybrid AC/DC Distribution Network

With the rapid development of power electronic technology and the wide application of distributed generation technology,DC power distribution technology has become a hot research topic at home and abroad.Hybrid AC/DC distribution network,which is used as the transition state of AC distribution network to DC distribution network,has been applied in many fields.Via AC and DC buses,a hybrid AC/DC distribution network can take advantages of different types of distributed generation(DG)units to meet AC and DC loads demand requirements respectively with less energy conversion stages.So the system can operate with improved energy conversion efficiency,economy and reliability.Researches on the stable operation and control have been paid much more attention for a long time.In this dissertation,some control methods to improve the hybrid AC/DC distribution network stability are systematically and thoroughly studied.This dissertation established the coal bed gas field hybrid AC/DC distribution network by DIgSILENT simulation software.The coal bed gas field distribution network contains photovoltaic generator,small gas combustion engines and oilfield oil pumping machine load models.The result of simulation showed that the established power grid could reflect characteristics of the hybrid AC/DC distribution network and lay the foundation for the simulation of the stable control strategy.In order to improve the distribution network small disturbance stability and the dynamic performance of the small gas combustion engines,terminal sliding mode additional excitation control based on the extended state observer was added to small gas combustion engines.The simulation results showed that the nonlinear robust additional excitation control can effectively increase the system damping and improve the small disturbance stability of the system.In the hybrid AC/DC distribution network of the coal bed gas feild,the DC bus voltage can be controlled directly by the bidirectional AC/DC converter.In order to overcome the disadvantages of the traditional double closed loop control strategy,this dissertation designed a nonlinear robust current feed forward control strategy based on extended state observer and terminal sliding mode control.The simulation results showed that the double closed loop control strategy based on feed forward current can better suppress the voltage fluctuation caused by load change.