Research On Unified Power Flow Controller Based On Two-Stage Matrix Converter

Unified power flow controller (UPFC) is the most promising device in the FACTS, whose flexibility manifests in a variety control functions, for instance, controlling the impedance and angle of power system, adjusting real power and reactive power to accord with the system needs. Two-stage matrix converter (TSMC) with reduced switches in its topology is also called the new frequency convertor. Compared with the conventional matrix converter (CMC), TSMC has many significant advantages, such as, adjusted input power factor, changed output voltage and reversibly flowing energy. On the other hand, TSMC is in fact much more welcome than CMC, because it gets rid of the complicated algorithm of line commutation and removes a huge capacitance in the DC port. So using TSMC to design UPFC not only meets the topologly of UPFC, but also makes the structrue and volume of UPFC more perfect.This dissertation starts with the topology of TSMC, proposing the double space vector modulation (SVM) with zero vector in the rectifier to control TSMC’s swicths, which can supply constant output voltage and enough reactive power. By analyzing the switching function of TSMC, the low frequency switching function and a simplified algorithm of SVM are acquired, whose simulation shows the simplified method is correct. The important assignment of this dissertation is to design UPFC based on TSMC and use it to control the power flow timely. The inverter of TSMC is considered as the controlled object, then the system input disturbances emerge on the DC port. However,controlling the output voltage can promote the input anti-interference ability. The mathematics model of TSMC inverter based on complex vector is an equivalent and easy controlled SI/SO model in the synchronous coordinate system, concluding that the single closed-loop voltage PI control can not eliminate disturbance influence quickly from the analysis.Based on the above facts, the voltage and current closed-loop controlling strategy and the PI control law are adopted to control TSMC to output the constant voltage. Because the PI controller is not able to acheive no static error when tracking sine, the park transform to be used to change a three-phase static sine into two phase rotating DC (3s/2r). Meanwhile, methods of the transmission function, the root-locus and the frequency response are taken to research a decoupling controller. Finally, a plural PI controller is put forward, not only can it solve the coupling effect between the d-q axis but also guarantee the dynamic and steady performance and the good output waveforms. After the complex vector model of UPFC based on TSMC is established and analyzed, the controlling strategy of a three-closed-loop (current, voltage and power) with the plural PI control law is applied to realize the new type UPFC of its power flow control. The simulation model is built according to the real power system with UPFC, whose simulation based on MTALAB/Simulink. Comparing the output and error waveforms about three kinds of controlling methods on TSMC, it is clear that the double closed-loop plural PI control is a effective way. Therefore, the similar method is introduced to control the new type UPFC, whose simulation results demonstrate that the closed-loop plural PI controlling strategy is available for stability and speedability requirement. So the design of UPFC based on TSMC is reasonable and feasible.