Design And Realization Of The Parallel Converter Of UPFC

Nowadays the development orientation of electric power system of all countries in the world is that more and more transmission-line systems of electric power system is connected each other. Moreover the configurations of the electric power system nets connected are more and more complicated and their operation duty is more and more burdensome. The development of electric power system need some new technologies for control the power flow, then the Flexible Alternating Current Transparent System (FACTS) technology can cater for the need and rapidly develop(make great progress). So as the versatile FACTS'controller, the Unified Power Flow Controller (UPFC) has more the ability for control power flow and more development space. In this dissertation, the basic operation principles and conventional transmission control capabilities of the UPFC are firstly analyzed. And the principle of independent real and reactive power flow control is illuminated in detail. The integer control frame and several control patterns are put forward in term of the characteristic of the UPFC. The relations of the amplitude and the phase of the injected voltage by the series converter of the UPFC are defined in difference control patterns. The control strategy of the parallel converter of the UPFC is put forward in term of its function. Based on the instantaneous circuit connection topology which is decided by the switch function, the original mathematic model of the parallel converter was set up. The average state space method was employed to eliminate the discontinuous feature of the switch function, then the average state space mathematic model was obtained. Using coordinate transformation, the orders of mathematic model was reduced and the three phase ac variables are converted to dc variables. PWM technologies is retrospected simply, and the choice mode of switching vectors of the space vector PWM and the formulas which are used to calculate the vector operation time of the space vector PWM are provided. Based the definite control strategy and the detailed model of the parallel converter, the integer design process of control system of the parallel converter and the formulas which are used to calculate the control parameters are given. Based the characteristic of the dq rotation frame, the control system of the parallel converter adopts double closed loop which use proportion-integral regulator. The control system of d axis consists of the voltage regulator and the current regulator, and the dc current of the series converter is fed to the current loop for dynamic respond of the parallel converter. The control system of q axis consists of the voltage regulator which uses droop regulator and the current regulator. The control system is decoupled by the dq current feedback. The d axis direction is defined by the three phases synthesized vector, so the parallel converter regulates real and reactive power easily and the high quality voltage and power factor are obtained. The design result is validated by MATLAB/SIMULINK. The apparatus parameters of the main circuit are designed in detail according in term of the performance index of the parallel converter.The function of the parallel converter is validated by the experiments.