Design And Test Of Unified Power Flow Controller With Fault Current Limiting

Nowadays, Power system has entered a stage of rapid development through constant change and development, which puts forward higher requirements to the power system. Unified power flow controller with fault current Limiting(UPFC-FCL) is receiving attention of the academic and industry circles at home and abroad, as a new generation of FACTS devices which keep a good balance on the transmission capacity, stability of the system and short circuit level. In this dissertation, several key issues in the design of UPFC-FCL are amply discussed following a literature review.First, the theoretical basis of the traditional UPFC, UPFC-FCL and optimized topology is discussed. The working principle and mathematical model of the traditional UPFC, and its impact on the power characteristics of the transmission system is analyzed. Followed by a discussion of the topology of UPFC-FCL, proposed by laboratory research group, and its dynamic process of current limiting and is analyzed, then its mathematical model is thereby establish. On the basis of the above analysis, topologies based on resonant turn-off control, fault current control, and modular multi-level converter(MMC) are put forward and simulated, which are able to speed up the cutting speed after the fault, control the fault current and enhance the quality of the output waveform respectively. The impact to the transient stability of the system of UPFC-FCL is also discussed and simulated in the three machines nine node system.Secondly, the design of protection system and control system of UPFC-FCL prototype is discussed. Detailed analysis of potential risks of overcurrent and output overvoltage without protection system of the UPFC-FCL in practical engineering applications is realized. A set of detailed overcurrent protection circuit and overvoltage protection circuit is designed, which acts automatically and without no delay. Contrast simulation and experimental results are provided to verify the importance and reliability of the protection circuit; Based on the space vector of three phase symmetrical system, its two-phase stationary coordinate system (αβ coordinate system) representation and Clark transform, two-phase rotating coordinate system(dq coordinate system) representation and park transformation, three-phase instantaneous power of corresponding coordinate system and three-phase phase-locked loop(PLL) technology is derived. Based on the above theory, the converter level control of UPFC-FCL based on a dual loop controller and a valve group level control of UPFC-FCL base on SPWM and SVPWM is descripted in detail. Afterwards, three control methods of the FCL module is proposed, and their advantages and disadvantages are also analyzed separately. At last, coordinated control strategy of the UPFC module and the FCL module is discussed when the UPFC-FCL device starts, runs, fault current limits, stops and in other work states in order to ensure the stable operation of the device.Finally, the experimental system design of UPFC-FCL is discussed taking the lOkV experimental prototype as an example. Parameters design for the key equipment of UPFC-FCL (dc capacitor and current limiting reactor) is reviewed, and proposed a ring system wiring which can eliminate one side of power supply and a high power system impedance. Site installation and system hardware layout is considered according to the experimental station site. Man-machine interaction system for understanding the device operating status and controlling the device operation is simply introduced, and experimental procedure is given to guide the experiment. A 10kV UPFC-FCL prototype is built and tested according to the design method given in this dissertation. Experiments including start up, reactive power control, power control and fault condition were performed, respectively. Experimental results prove the performance of the UPFC-FCL, and its reliability and feasibility.