The Topology And Power Flow Regulation Application Research Of High-voltage Hybrid Unified Power Flow Controller

Due to the uneven distribution of primary energy and electricity load,large-scale extra high voltage(EHV)and ultra high voltage(UHV)transmission lines have been constructed in China.However,the power flow distribution of the grid is determined by the grid injection mode and the grid structure and parameters,the utilization rates of the existing EHV and UHV grids are seriously insufficient.Besides,due to the environmental and land resources factors,it is increasingly difficult to build new transmission corridors.Therefore,an effective power flow control device is urgently needed to control the power flow in high voltage power systems.It can be used to improve the utilization rate of transmission line and enhance the transmission capacity of the existing power grid.As the most powerful FACTS device,the UPFC can adjust the power flow quickly and continuously.Due to the high cost,large switching losses and low reliability,UPFC is not suitable for large-scale application in EHV and UHV grids.It is more suitable for the applications requiring fast dynamic response.Compared to UPFC,the "Sen" transformer(ST)can achieve similar power flow adjustment effects with low cost,low loss and high reliability.However,the regulation of the ST is discontinuous.The hybrid electromagnetic unified power flow controller(HEUPFC)can control the power flow continuously with low cost,low loss and high reliability.However,the HEUPFC and the ST are only suitable for power systems with voltage levels below 220 k V.According to the deficiencies of the existing power flow regulation technology,this paper proposes a high-voltage hybrid unified power flow controller.This paper focuses on the topology,principles,control strategy and applications of the device.The main work and innovations of this paper are as follows.(1)A high-voltage "Sen" transformer(HVST)is proposed in this paper,consisting of a three-phase two-winding transformer and two sets of tap changers.The series compensating voltages produced by the HVST are injected in the transmission line via an isolation transformer.The isolation transformer reduces the insulation requirements for the series windings and tap changers of the HVST,which makes the HVST more suitable for high-voltage power systems than the ST.The HVST utilizes the primary winding of the transformer to provide a partial series regulation voltage and improves the connection mode of series windings,in this way,the HVST has a simpler structure and bigger phase-shift range and power flow regulatory region than the ST.The structure,operational principles,and power flow regulation principles of the HVST are analyzed in this paper.Then a detailed comparison between the ST and the HVST is made.The simulation in a two-area test system has been used to prove the effectiveness and advantages of the HVST.(2)Since the HVST cannot adjust the power flow continuously,this paper further proposes a high-voltage hybrid unified power flow controller(HHUPFC).HHUPFC combines a large capacity HVST with a small capacity UPFC,it can provide a continuous power flow control.Since the traditional HEUPFC still adopts the structure of ST,the HHUPFC is more suitable for high voltage system than the HEUPFC.In this paper,the capacity relationship between the HVST and the UPFC in a HHUPFC is derived.Based on the analysis of the voltage regulation principle,the four power flow adjustment functions of HHUPFC are introduced in detail.Then,the power flow control strategy of HHUPFC is proposed.Besides,the comparisons among HEUPFC and HHUPFC are analyzed in detail.Compared to HVST,HHUPFC improves the accuracy of power flow adjustment.Compared to HEUPFC,HHUPFC has larger phase shift range and power flow control region.Simulation studies are used to verify the practicability and superiority of the HHUPFC.(3)This paper studies the effects of HHUPFC on the power flow equalization and transmission capacity enhancement in multi-parallel lines and ring networks.Based on theoretical analysis,this paper compares the power flow balancing effects of HHUPFC and HEUPFC in IEEE39 bus system and IEEE30 bus system.Beside,in the typical example of Guangdong Power Grid,the transmission capacity improvement effects of HHUPFC and HEUPFC on multi-parallel lines and ring networks are compared.The simulation results show that in order to achieve the same power flow adjustment effect,the device capacity and cost of the HHUPFC proposed in this paper are much lower than that of the HEUPFC.(4)In this paper,a 10 k V HVST device is developed.The output voltage phase and winding ratio are tested to verify that the HVST meets the parameter design requirements.A10 k V experimental platform is built to verify the feasibility of HVST in voltage and power flow regulation.In addition,this paper builds a HVST and HHUPFC experimental model under laboratory conditions at low voltage and low power.The experimental results verify the advantages of the HHUPFC.The experimental research provides experimental basis for the application of HVST and HHUPFC in power system.It has reference significance for the HVST and HHUPFC development and parameter design.