The Topology And Control Strategy Of Distribution Network Reliable Power Supply Island

With the rapid development of distribution network,higher demands are being placed on reliability and quality of power supply by important load and sensitive load.Besides,an increasing number of penetration rate in distributed generation and controllable load also brings a great challenge to the operation of distribution network.In order to solve the problems lying in providing highly reliable and high quality power and promoting the intelligence of distribution network,this thesis presents the Reliable Power Supply Island(RPSI)power supply scheme and carries out research by concentrating on its topology,control strategy and setting method of command quantity.Firstly,this thesis proposes the topology of RPSI applied to three-phase four-wire system,expounds the scheme’s superiority for guaranteeing high reliability,high quality power as well as promoting the intelligence of distribution network in detail.The derivative topology is also proposed to meet the requirement of important load’s power supply in different scenarios and different levels of demand.Secondly,taking a double-sources and double-loads RPSI of three-phase four-wire system as the research object,this thesis analyzes the implementation of its basic functions and its operation mode under different working conditions.By establishing mathematical model of RPSI,this thesis puts forward the system level control strategy and confirms the command quantity.Theoretical analysis shows that except for changing the value of command quantity,there is no need to switch control mode when RPSI operates in different states.The calculation results verifies that the control strategy is effective for realizing RPSI’s basic functions.However,the results also prove that such unreasonable command quantity will lead to some convertors’ compensating voltage and current exceeding specified limits and cause a significant quantity of power circulation between converters,which dramatically reduces the operational efficiency of RPSI.Thirdly,regarding the problems above,a reasonable setting range of command quantity is derived with the constraint conditions that the convertors’ compensating voltage and current is supposed to run across a logical range.Moreover,taking the minimized current of critical node and the restrained compensating voltage of converters as the optimization objective,the optimized setting value of command quantity is further solved under different working conditions.Finally,on the basis of the system level control strategy,the converter level control strategy is correspondingly proposed.According to the two control strategies,a detailed simulation model of RPSI is built in Matlab/Simulink,making use of the optimal command quantity,to test its realizability.Simulation results show that the control strategies and the optimal command quantity can not only guarantee providing highly reliable and high quality power under different working conditions,but also optimize the island’s operation,making every converter output voltage and current runs across a reasonable range,eliminating power circulation between converters and coordinating the power distribution of reactive power supply.