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

Unified power flow controller (UPFC), a typical and the most flexible controller of FACTS, could control the impedance, angle, and the real and reactive power flow of transmission line. Two-stage matrix converter (TSMC) is the direct frequency converting device of a new topology. Compared with conventional matrix converter (CMC), TSMC not only has the same choiceness characteristics, for example, the input power factor is adjustable, the output voltage is adjustable, the flow of the energy is two-way and so on, but also gets over the trouble belonged to CMC, such as unnecessary complicated four step commutation and so on. So if TSMC is applied in UPFC, TSMC meets the demand of UPFC, moreover it removes the huge capacitance compared with the traditional AC-DC-AC converter, the volume is reduced, the efficiency is enhanced.Firstly the topology of two-stage matrix converter, the double space vector modulation strategy and the low frequency switching functions were analysed in the paper, and a simplified algorithm of two-stage matrix converter was proposed, then this paper made deep investigation on the closed-loop control of TSMC and the application of TSMC in UPFC. In this paper, inverter stage of TSMC is regarded as controlled plant, input disturbances are regarded as DC disturbances. The mathematics model of inverter stage was constructed on three phase static coordinate, based on which the compound vector model of inverter stage was constructed, which simplifies the model from a multi-input/ multi-output system to an equivalent single-input/single-output system. Based on these models, the voltage current double closed-loop control strategy of two-stage matrix converter was proposed, and through the analysis and the design to the control system by the conventional method, for example, transmission function method, root-locus method, frequency response method, a plural PI controller was proposed in the current inner loop and the voltage outer loop separately and realized the decoupling control. Finally UPFC based on TSMC was researched and designed in this paper, through establishing and analyzing the complex vector model of UPFC based on TSMC, a three-loop control strategy was proposed, and the controllers were designed by the analysis of the complex vector transfer function for realizing the decoupling control.The simulation model was built and analyzed by matlab software in the paper, the simulation results demonstrated the feasibility and validity of the method presented. At the same time TSMC experimental sample device was trial-manufactured by DSP as the control core, of which results verified its modulation strategy validity.