Research On Operating Characteristics And Device-level Design Of Distributed Power Flow Controller

With the rapid development of China's economy,the social power demand continues to increase.To further improve the stability,the flexibility of power system and the balance of power resource allocation,many related technologies have emerged,such as the distributed generation,the regional power grid interconnection,the smart grid.These technologies pose new challenges to power flow control technology.The practical application of FACTS provides abundant adjustment methods for power systems,among them the unified power flow controller(UPFC)can flexibly regulates the power flow,and be able to improve the system stability.But it's special topology makes the internal fault current easy to spread,the extensive use of high-voltage,high-power devices increases device losses and insulation requirements,the High investment costs and difficult maintenance restricted the practical application of UPFC.Distributed Power Flow Controller(DPFC)was born on this basis.It has the same power flow control performance of UPFC,in addition to this,its power regulation method is more flexible,it has smaller capacity,lower cost and easier maintenance than UPFC.These advantages make DPFC have broader application perspective than UPFC.This thesis studies the control characteristics of DPFC,the modeling of controller,the verification of power flow control performance,and the hardware and software design of the device.First,the equivalent circuit model of DPFC is analyzed,In DPFC,the active power is transmitted between DPFC's series converter and parallel converter through Third harmonic power.various operating modes are explained.Through the establishment and derivation of the mathematical model,the DPFC's fundamental frequency power control range was obtained,considering the third harmonic,the control range is expanded.Then,the three-level control scheme is proposed,including dispatching level,system level,device level,the signal transmission content and direction between levels are determined.The controller model of the parallel side and series side is established,which is based on PI control.A DPFC application example in set up in PSCAD/EMTDC,the results show that DPFC can independently regulate steady-state active and reactive power of power lines,and in the event of a short-circuit fault,the power disturbance of the line can be reduced by DPFC.At last,in accordance with the procedures of data acquisition,A/D conversion,electrical parameter calculation,control strategy implementation,storage and communication,the hardware and software architecture solution of DPFC is designed,A fast frequency measurement algorithm applied to power system is proposed and the application of singlephase PLL in the device is verified.Considering the particularity of the installation location of the DPFC series side unit,a closed-loop communication system based on power line carrier communication and WAMS system parameter feedback was designed to achieve the overall closed-loop control of DPFC.